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Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree [message #46339 is a reply to message #46338] Fri, 11 May 2012 18:42 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *virtua.com.br
On 05/11/2012 03:32 PM, Christoph Lameter wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>> Thank you in advance for your time reviewing this!
>
> Where do I find the rationale for all of this? Trouble is that pages can
> contain multiple objects f.e. so accounting of pages to groups is a bit fuzzy.
> I have not followed memcg too much since it is not relevant (actual
> it is potentially significantly harmful given the performance
> impact) to the work loads that I am using.
>
It's been spread during last discussions. The user-visible part is
documented in the last patch, but I'll try to use this space here to
summarize more of the internals (it can also go somewhere in the tree
if needed):

We want to limit the amount of kernel memory tasks inside a memory
cgroup use. slab is not the only one of them, but it is quite significant.

For that, the least invasive, and most reasonable way we found to do it,
is to create a copy of each slab inside the memcg. Or almost: we lazy
create them, so only slabs that are touched by the memcg are created.

So we don't mix pages from multiple memcgs in the same cache - we
believe that would be too confusing.

/proc/slabinfo reflects this information, by listing the memcg-specific
slabs.

This also appears in a memcg-specific memory.kmem.slabinfo.

Also note that accounting is not done until kernel memory is limited.
And if no memcg is limited, the code is wrapped inside static_key
branches. So it should be completely patched out if you don't put stuff
inside memcg.
Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree [message #46340 is a reply to message #46339] Fri, 11 May 2012 18:56 Go to previous messageGo to next message
Christoph Lameter is currently offline  Christoph Lameter
Messages: 123
Registered: September 2006
Senior Member
From: *parallels.com
On Fri, 11 May 2012, Glauber Costa wrote:

> So we don't mix pages from multiple memcgs in the same cache - we believe that
> would be too confusing.

Well subsystem create caches and other things that are shared between
multiple processes. How can you track that?

> /proc/slabinfo reflects this information, by listing the memcg-specific slabs.

What about /sys/kernel/slab/*?
Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree [message #46341 is a reply to message #46340] Fri, 11 May 2012 18:58 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *virtua.com.br
On 05/11/2012 03:56 PM, Christoph Lameter wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>> So we don't mix pages from multiple memcgs in the same cache - we believe that
>> would be too confusing.
>
> Well subsystem create caches and other things that are shared between
> multiple processes. How can you track that?

Each process that belongs to a memcg triggers the creation of a new
child kmem cache.

>> /proc/slabinfo reflects this information, by listing the memcg-specific slabs.
>
> What about /sys/kernel/slab/*?

From the PoV of the global system, what you'll see is something like:
dentry , dentry(2:memcg1), dentry(2:memcg2), etc.

No attempt is made to provide any view of those caches in a logically
grouped way - the global system can view them independently.
Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree [message #46342 is a reply to message #46341] Fri, 11 May 2012 19:09 Go to previous messageGo to next message
Christoph Lameter is currently offline  Christoph Lameter
Messages: 123
Registered: September 2006
Senior Member
From: *parallels.com
On Fri, 11 May 2012, Glauber Costa wrote:

> On 05/11/2012 03:56 PM, Christoph Lameter wrote:
> > On Fri, 11 May 2012, Glauber Costa wrote:
> >
> > > So we don't mix pages from multiple memcgs in the same cache - we believe
> > > that
> > > would be too confusing.
> >
> > Well subsystem create caches and other things that are shared between
> > multiple processes. How can you track that?
>
> Each process that belongs to a memcg triggers the creation of a new child kmem
> cache.

I see that. But there are other subsystems from slab allocators that do
the same. There are also objects that may be used by multiple processes.
F.e what about shm?

> > > /proc/slabinfo reflects this information, by listing the memcg-specific
> > > slabs.
> >
> > What about /sys/kernel/slab/*?
>
> From the PoV of the global system, what you'll see is something like:
> dentry , dentry(2:memcg1), dentry(2:memcg2), etc.

Hmmm.. Would be better to have a hierachy there. /proc/slabinfo is more
legacy.
Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree [message #46343 is a reply to message #46342] Fri, 11 May 2012 19:11 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *virtua.com.br
On 05/11/2012 04:09 PM, Christoph Lameter wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>> On 05/11/2012 03:56 PM, Christoph Lameter wrote:
>>> On Fri, 11 May 2012, Glauber Costa wrote:
>>>
>>>> So we don't mix pages from multiple memcgs in the same cache - we believe
>>>> that
>>>> would be too confusing.
>>>
>>> Well subsystem create caches and other things that are shared between
>>> multiple processes. How can you track that?
>>
>> Each process that belongs to a memcg triggers the creation of a new child kmem
>> cache.
>
> I see that. But there are other subsystems from slab allocators that do
> the same. There are also objects that may be used by multiple processes.

This is also true for normal user pages. And then, we do what memcg
does: first one to touch, gets accounted. I don't think deviating from
the memcg behavior for user pages makes much sense here.

A cache won't go away while it still have objects, even after the memcg
is removed (it is marked as dead)

> F.e what about shm?
>
>>>> /proc/slabinfo reflects this information, by listing the memcg-specific
>>>> slabs.
>>>
>>> What about /sys/kernel/slab/*?
>>
>> From the PoV of the global system, what you'll see is something like:
>> dentry , dentry(2:memcg1), dentry(2:memcg2), etc.
>
> Hmmm.. Would be better to have a hierachy there. /proc/slabinfo is more
> legacy.

I can take a look at that then. Assuming you agree with all the rest, is
looking into that a pre-requisite for merging, or is something that can
be deferred for a phase2 ? (We still don't do shrinkers, for instance,
so this is sure to have a phase2)
Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree [message #46344 is a reply to message #46343] Fri, 11 May 2012 19:20 Go to previous messageGo to next message
Christoph Lameter is currently offline  Christoph Lameter
Messages: 123
Registered: September 2006
Senior Member
From: *parallels.com
On Fri, 11 May 2012, Glauber Costa wrote:

> > I see that. But there are other subsystems from slab allocators that do
> > the same. There are also objects that may be used by multiple processes.
>
> This is also true for normal user pages. And then, we do what memcg does:
> first one to touch, gets accounted. I don't think deviating from the memcg
> behavior for user pages makes much sense here.
>
> A cache won't go away while it still have objects, even after the memcg is
> removed (it is marked as dead)

Ok so we will have some dead pages around that are then repatriated to
the / set?

> > Hmmm.. Would be better to have a hierachy there. /proc/slabinfo is more
> > legacy.
>
> I can take a look at that then. Assuming you agree with all the rest, is
> looking into that a pre-requisite for merging, or is something that can be
> deferred for a phase2 ? (We still don't do shrinkers, for instance, so this is
> sure to have a phase2)

Not a prerequisite for merging but note that I intend to rework the
allocators to extract common code so that they have the same sysfs
interface, error reporting and failure scenarios. We can at that time
also add support for /sys/kernel/slab to memcg. (/sys/memcg/<name>/slab/* ?)
Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree [message #46345 is a reply to message #46344] Fri, 11 May 2012 19:24 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *virtua.com.br
On 05/11/2012 04:20 PM, Christoph Lameter wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>>> I see that. But there are other subsystems from slab allocators that do
>>> the same. There are also objects that may be used by multiple processes.
>>
>> This is also true for normal user pages. And then, we do what memcg does:
>> first one to touch, gets accounted. I don't think deviating from the memcg
>> behavior for user pages makes much sense here.
>>
>> A cache won't go away while it still have objects, even after the memcg is
>> removed (it is marked as dead)
>
> Ok so we will have some dead pages around that are then repatriated to
> the / set?

No, they are not repatriated. I actually wrote code for that once in my
first series, but it was the general feeling at the time that it was too
complicated. (and I only tried for the slub, not slab)

So instead, we just keep the cache around, until the objects go away.
It will show in slabinfo as dentry(css_id:memcgname)dead

For the record, I wrote that code because I found a nice feature, but I
totally agree with the complicated part.

Also, in normal scenarios, dead caches are not expected to be common.
Most of them should go away as memcg dies.

>>> Hmmm.. Would be better to have a hierachy there. /proc/slabinfo is more
>>> legacy.
>>
>> I can take a look at that then. Assuming you agree with all the rest, is
>> looking into that a pre-requisite for merging, or is something that can be
>> deferred for a phase2 ? (We still don't do shrinkers, for instance, so this is
>> sure to have a phase2)
>
> Not a prerequisite for merging but note that I intend to rework the
> allocators to extract common code so that they have the same sysfs
> interface, error reporting and failure scenarios. We can at that time
> also add support for /sys/kernel/slab to memcg. (/sys/memcg/<name>/slab/* ?)

Yes, that would be a good plan.
Re: [PATCH v2 19/29] skip memcg kmem allocations in specified code regions [message #46359 is a reply to message #46320] Tue, 15 May 2012 02:46 Go to previous messageGo to next message
KAMEZAWA Hiroyuki is currently offline  KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
Senior Member
From: *parallels.com
(2012/05/12 2:44), Glauber Costa wrote:

> This patch creates a mechanism that skip memcg allocations during
> certain pieces of our core code. It basically works in the same way
> as preempt_disable()/preempt_enable(): By marking a region under
> which all allocations will be accounted to the root memcg.
>
> We need this to prevent races in early cache creation, when we
> allocate data using caches that are not necessarily created already.
>
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>


The concept seems okay to me but...

> ---
> include/linux/sched.h | 1 +
> mm/memcontrol.c | 25 +++++++++++++++++++++++++
> 2 files changed, 26 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 81a173c..0501114 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1613,6 +1613,7 @@ struct task_struct {
> unsigned long nr_pages; /* uncharged usage */
> unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
> } memcg_batch;
> + atomic_t memcg_kmem_skip_account;


If only 'current' thread touch this, you don't need to make this atomic counter.
you can use 'long'.

Thanks,
-Kame
Re: [PATCH v2 18/29] memcg: kmem controller charge/uncharge infrastructure [message #46360 is a reply to message #46319] Tue, 15 May 2012 02:57 Go to previous messageGo to next message
KAMEZAWA Hiroyuki is currently offline  KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
Senior Member
From: *parallels.com
(2012/05/12 2:44), Glauber Costa wrote:

> With all the dependencies already in place, this patch introduces
> the charge/uncharge functions for the slab cache accounting in memcg.
>
> Before we can charge a cache, we need to select the right cache.
> This is done by using the function __mem_cgroup_get_kmem_cache().
>
> If we should use the root kmem cache, this function tries to detect
> that and return as early as possible.
>
> The charge and uncharge functions comes in two flavours:
> * __mem_cgroup_(un)charge_slab(), that assumes the allocation is
> a slab page, and
> * __mem_cgroup_(un)charge_kmem(), that does not. This later exists
> because the slub allocator draws the larger kmalloc allocations
> from the page allocator.
>
> In memcontrol.h those functions are wrapped in inline acessors.
> The idea is to later on, patch those with jump labels, so we don't
> incur any overhead when no mem cgroups are being used.
>
> Because the slub allocator tends to inline the allocations whenever
> it can, those functions need to be exported so modules can make use
> of it properly.
>
> I apologize in advance to the reviewers. This patch is quite big, but
> I was not able to split it any further due to all the dependencies
> between the code.
>
> This code is inspired by the code written by Suleiman Souhlal,
> but heavily changed.
>
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> ---
> include/linux/memcontrol.h | 67 ++++++++
> init/Kconfig | 2 +-
> mm/memcontrol.c | 379 +++++++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 446 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index f93021a..c555799 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -21,6 +21,7 @@
> #define _LINUX_MEMCONTROL_H
> #include <linux/cgroup.h>
> #include <linux/vm_event_item.h>
> +#include <linux/hardirq.h>
>
> struct mem_cgroup;
> struct page_cgroup;
> @@ -447,6 +448,19 @@ void mem_cgroup_register_cache(struct mem_cgroup *memcg,
> void mem_cgroup_release_cache(struct kmem_cache *cachep);
> extern char *mem_cgroup_cache_name(struct mem_cgroup *memcg,
> struct kmem_cache *cachep);
> +
> +void mem_cgroup_flush_cache_create_queue(void);
> +bool __mem_cgroup_charge_slab(struct kmem_cache *cachep, gfp_t gfp,
> + size_t size);
> +void __mem_cgroup_uncharge_slab(struct kmem_cache *cachep, size_t size);
> +
> +bool __mem_cgroup_new_kmem_page(struct page *page, gfp_t gfp);
> +void __mem_cgroup_free_kmem_page(struct page *page);
> +
> +struct kmem_cache *
> +__mem_cgroup_get_kmem_cache(struct kmem_cache *cachep, gfp_t gfp);
> +
> +#define mem_cgroup_kmem_on 1
> #else
> static inline void mem_cgroup_register_cache(struct mem_cgroup *memcg,
> struct kmem_cache *s)
> @@ -463,6 +477,59 @@ static inline void sock_update_memcg(struct sock *sk)
> static inline void sock_release_memcg(struct sock *sk)
> {
> }
> +
> +static inline void
> +mem_cgroup_flush_cache_create_queue(void)
> +{
> +}
> +
> +static inline void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
> +{
> +}
> +
> +#define mem_cgroup_kmem_on 0
> +#define __mem_cgroup_get_kmem_cache(a, b) a
> +#define __mem_cgroup_charge_slab(a, b, c) false
> +#define __mem_cgroup_new_kmem_page(a, gfp) false
> +#define __mem_cgroup_uncharge_slab(a, b)
> +#define __mem_cgroup_free_kmem_page(b)
> #endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
> +static __always_inline struct kmem_cache *
> +mem_cgroup_get_kmem_cache(struct kmem_cache *cachep, gfp_t gfp)
> +{
> + if (mem_cgroup_kmem_on && current->mm && !in_interrupt())
> + return __mem_cgroup_get_kmem_cache(cachep, gfp);
> + return cachep;
> +}
> +
> +static __always_inline bool
> +mem_cgroup_charge_slab(struct kmem_cache *cachep, gfp_t gfp, size_t size)
> +{
> + if (mem_cgroup_kmem_on)
> + return __mem_cgroup_charge_slab(cachep, gfp, size);
> + return true;
> +}
> +
> +static __always_inline void
> +mem_cgroup_uncharge_slab(struct kmem_cache *cachep, size_t size)
> +{
> + if (mem_cgroup_kmem_on)
> + __mem_cgroup_uncharge_slab(cachep, size);
> +}
> +
> +static __always_inline
> +bool mem_cgroup_new_kmem_page(struct page *page, gfp_t gfp)
> +{
> + if (mem_cgroup_kmem_on && current->mm && !in_interrupt())
> + return __mem_cgroup_new_kmem_page(page, gfp);
> + return true;
> +}
> +
> +static __always_inline
> +void mem_cgroup_free_kmem_page(struct page *page)
> +{
> + if (mem_cgroup_kmem_on)
> + __mem_cgroup_free_kmem_page(page);
> +}
> #endif /* _LINUX_MEMCONTROL_H */
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 72f33fa..071b7e3 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -696,7 +696,7 @@ config CGROUP_MEM_RES_CTLR_SWAP_ENABLED
> then swapaccount=0 does the trick).
> config CGROUP_MEM_RES_CTLR_KMEM
> bool "Memory Resource Controller Kernel Memory accounting (EXPERIMENTAL)"
> - depends on CGROUP_MEM_RES_CTLR && EXPERIMENTAL
> + depends on CGROUP_MEM_RES_CTLR && EXPERIMENTAL && !SLOB
> default n
> help
> The Kernel Memory extension for Memory Resource Controller can limit
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a8171cb..5a7416b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -10,6 +10,10 @@
> * Copyright (C) 2009 Nokia Corporation
> * Author: Kirill A. Shutemov
> *
> + * Kernel Memory Controller
> + * Copyright (C) 2012 Parallels Inc. and Google Inc.
> + * Authors: Glauber Costa and Suleiman Souhlal
> + *
> * This program is free software; you can redistribute it and/or modify
> * it under the terms of the GNU General Public License as published by
> * the Free Software Foundation; either version 2 of the License, or
> @@ -321,6 +325,11 @@ struct mem_cgroup {
> #ifdef CONFIG_INET
> struct tcp_memcontrol tcp_mem;
> #endif
> +
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> + /* Slab accounting */
> + struct kmem_cache *slabs[MAX_KMEM_CACHE_TYPES];
> +#endif
> };
>
> int memcg_css_id(struct mem_cgroup *memcg)
> @@ -414,6 +423,9 @@ static void mem_cgroup_put(struct mem_cgroup *memcg);
> #include <net/ip.h>
>
> static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
> +static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, s64 delta);
> +static void memcg_uncharge_kmem(struct mem_cgroup *memcg, s64 delta);
> +
> void sock_update_memcg(struct sock *sk)
> {
> if (mem_cgroup_sockets_enabled) {
> @@ -484,7 +496,14 @@ char *mem_cgroup_cache_name(struct mem_cgroup *memcg, struct kmem_cache *cachep)
> return name;
> }
>
> +static inline bool mem_cgroup_kmem_enabled(struct mem_cgroup *memcg)
> +{
> + return !mem_cgroup_disabled() && memcg &&
> + !mem_cgroup_is_root(memcg) && memcg->kmem_accounted;
> +}
> +
> struct ida cache_types;
> +static DEFINE_MUTEX(memcg_cache_mutex);
>
> void mem_cgroup_register_cache(struct mem_cgroup *memcg,
> struct kmem_cache *cachep)
> @@ -504,6 +523,298 @@ void mem_cgroup_release_cache(struct kmem_cache *cachep)
> if (cachep->memcg_params.id != -1)
> ida_simple_remove(&cache_types, cachep->memcg_params.id);
> }
> +
> +
> +static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
> + struct kmem_cache *cachep)
> +{
> + struct kmem_cache *new_cachep;
> + int idx;
> +
> + BUG_ON(!mem_cgroup_kmem_enabled(memcg));
> +
> + idx = cachep->memcg_params.id;
> +
> + mutex_lock(&memcg_cache_mutex);
> + new_cachep = memcg->slabs[idx];
> + if (new_cachep)
> + goto out;
> +
> + new_cachep = kmem_cache_dup(memcg, cachep);
> +
> + if (new_cachep == NULL) {
> + new_cachep = cachep;
> + goto out;
> + }
> +
> + mem_cgroup_get(memcg);
> + memcg->slabs[idx] = new_cachep;
> + new_cachep->memcg_params.memcg = memcg;
> + atomic_set(&new_cachep->memcg_params.refcnt, 1);
> +out:
> + mutex_unlock(&memcg_cache_mutex);
> + return new_cachep;
> +}
> +
> +struct create_work {
> + struct mem_cgroup *memcg;
> + struct kmem_cache *cachep;
> + struct list_head list;
> +};
> +
> +/* Use a single spinlock for destruction and creation, not a frequent op */
> +static DEFINE_SPINLOCK(cache_queue_lock);
> +static LIST_HEAD(create_queue);
> +
> +/*
> + * Flush the queue of kmem_caches to create, because we're creating a cgroup.
> + *
> + * We might end up flushing other cgroups' creation requests as well, but
> + * they will just get queued again next time someone tries to make a slab
> + * allocation for them.
> + */
> +void mem_cgroup_flush_cache_create_queue(void)
> +{
> + struct create_work *cw, *tmp;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&cache_queue_lock, flags);
> + list_for_each_entry_safe(cw, tmp, &create_queue, list) {
> + list_del(&c
...

Re: [PATCH v2 11/29] cgroups: ability to stop res charge propagation on bounded ancestor [message #46361 is a reply to message #46310] Tue, 15 May 2012 02:59 Go to previous messageGo to next message
KAMEZAWA Hiroyuki is currently offline  KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
Senior Member
From: *parallels.com
(2012/05/12 2:44), Glauber Costa wrote:

> From: Frederic Weisbecker <fweisbec@gmail.com>
>
> Moving a task from a cgroup to another may require to substract its
> resource charge from the old cgroup and add it to the new one.
>
> For this to happen, the uncharge/charge propagation can just stop when we
> reach the common ancestor for the two cgroups. Further the performance
> reasons, we also want to avoid to temporarily overload the common
> ancestors with a non-accurate resource counter usage if we charge first
> the new cgroup and uncharge the old one thereafter. This is going to be a
> requirement for the coming max number of task subsystem.
>
> To solve this, provide a pair of new API that can charge/uncharge a
> resource counter until we reach a given ancestor.
>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Acked-by: Paul Menage <paul@paulmenage.org>
> Acked-by: Glauber Costa <glommer@parallels.com>
> Cc: Li Zefan <lizf@cn.fujitsu.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Aditya Kali <adityakali@google.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Kay Sievers <kay.sievers@vrfy.org>
> Cc: Tim Hockin <thockin@hockin.org>
> Cc: Tejun Heo <htejun@gmail.com>
> Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>


Where is this function called in this series ?

Thanks,
-Kame
Re: [PATCH v2 02/29] slub: fix slab_state for slub [message #46364 is a reply to message #46305] Tue, 15 May 2012 21:55 Go to previous messageGo to next message
David Rientjes is currently offline  David Rientjes
Messages: 59
Registered: November 2006
Member
From: *parallels.com
On Fri, 11 May 2012, Glauber Costa wrote:

> When the slub code wants to know if the sysfs state has already been
> initialized, it tests for slab_state == SYSFS. This is quite fragile,
> since new state can be added in the future (it is, in fact, for
> memcg caches). This patch fixes this behavior so the test matches
> >= SYSFS, as all other state does.
>
> Signed-off-by: Glauber Costa <glommer@parallels.com>

Acked-by: David Rientjes <rientjes@google.com>

Can be merged now, there's no dependency on the rest of this patchset.
Re: [PATCH v2 05/29] slab: rename gfpflags to allocflags [message #46365 is a reply to message #46309] Tue, 15 May 2012 21:57 Go to previous messageGo to next message
David Rientjes is currently offline  David Rientjes
Messages: 59
Registered: November 2006
Member
From: *parallels.com
On Fri, 11 May 2012, Glauber Costa wrote:

> A consistent name with slub saves us an acessor function.
> In both caches, this field represents the same thing. We would
> like to use it from the mem_cgroup code.
>
> Signed-off-by: Glauber Costa <glommer@parallels.com>

Acked-by: David Rientjes <rientjes@google.com>

Same, can be merged now with no dependency on the rest of this patchset.
Re: [PATCH v2 01/29] slab: dup name string [message #46366 is a reply to message #46303] Tue, 15 May 2012 22:04 Go to previous messageGo to next message
David Rientjes is currently offline  David Rientjes
Messages: 59
Registered: November 2006
Member
From: *parallels.com
On Fri, 11 May 2012, Glauber Costa wrote:

> diff --git a/mm/slab.c b/mm/slab.c
> index e901a36..91b9c13 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2118,6 +2118,7 @@ static void __kmem_cache_destroy(struct kmem_cache *cachep)
> kfree(l3);
> }
> }
> + kfree(cachep->name);
> kmem_cache_free(&cache_cache, cachep);
> }
>
> @@ -2526,7 +2527,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
> BUG_ON(ZERO_OR_NULL_PTR(cachep->slabp_cache));
> }
> cachep->ctor = ctor;
> - cachep->name = name;
> + cachep->name = kstrdup(name, GFP_KERNEL);
>
> if (setup_cpu_cache(cachep, gfp)) {
> __kmem_cache_destroy(cachep);

Couple problems:

- allocating memory for a string of an unknown, unchecked size, and

- could potentially return NULL which I suspect will cause problems
later.
Re: [PATCH v2 02/29] slub: fix slab_state for slub [message #46368 is a reply to message #46364] Wed, 16 May 2012 06:10 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
On 05/16/2012 01:55 AM, David Rientjes wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>> When the slub code wants to know if the sysfs state has already been
>> initialized, it tests for slab_state == SYSFS. This is quite fragile,
>> since new state can be added in the future (it is, in fact, for
>> memcg caches). This patch fixes this behavior so the test matches
>>> = SYSFS, as all other state does.
>>
>> Signed-off-by: Glauber Costa<glommer@parallels.com>
>
> Acked-by: David Rientjes<rientjes@google.com>
>
> Can be merged now, there's no dependency on the rest of this patchset.

Agreed.

If anyone is willing to, would make my life easier in the future.

Valid for all patches that fall in this category (there are quite a few
in the purely memcg land as well)
Re: [PATCH v2 01/29] slab: dup name string [message #46369 is a reply to message #46366] Wed, 16 May 2012 06:12 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
On 05/16/2012 02:04 AM, David Rientjes wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>> diff --git a/mm/slab.c b/mm/slab.c
>> index e901a36..91b9c13 100644
>> --- a/mm/slab.c
>> +++ b/mm/slab.c
>> @@ -2118,6 +2118,7 @@ static void __kmem_cache_destroy(struct kmem_cache *cachep)
>> kfree(l3);
>> }
>> }
>> + kfree(cachep->name);
>> kmem_cache_free(&cache_cache, cachep);
>> }
>>
>> @@ -2526,7 +2527,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>> BUG_ON(ZERO_OR_NULL_PTR(cachep->slabp_cache));
>> }
>> cachep->ctor = ctor;
>> - cachep->name = name;
>> + cachep->name = kstrdup(name, GFP_KERNEL);
>>
>> if (setup_cpu_cache(cachep, gfp)) {
>> __kmem_cache_destroy(cachep);
>
> Couple problems:
>
> - allocating memory for a string of an unknown, unchecked size, and
>
> - could potentially return NULL which I suspect will cause problems
> later.

Well, this is what slub does.

I sent already two patches for it: One removing this from the slub, one
adding this to the slab.

Right now I am comfortable with this one, because it makes it slightly
easier in the latest patches of my series.

But note the word: slightest.

I am comfortable with any, provided slub and slab start behaving the same.

So whatever you guys decide between yourselves is fine, provided there
is a decision.

Thanks for your review, David!
Re: [PATCH v2 11/29] cgroups: ability to stop res charge propagation on bounded ancestor [message #46370 is a reply to message #46361] Wed, 16 May 2012 06:16 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
On 05/15/2012 06:59 AM, KAMEZAWA Hiroyuki wrote:
> (2012/05/12 2:44), Glauber Costa wrote:
>
>> From: Frederic Weisbecker<fweisbec@gmail.com>
>>
>> Moving a task from a cgroup to another may require to substract its
>> resource charge from the old cgroup and add it to the new one.
>>
>> For this to happen, the uncharge/charge propagation can just stop when we
>> reach the common ancestor for the two cgroups. Further the performance
>> reasons, we also want to avoid to temporarily overload the common
>> ancestors with a non-accurate resource counter usage if we charge first
>> the new cgroup and uncharge the old one thereafter. This is going to be a
>> requirement for the coming max number of task subsystem.
>>
>> To solve this, provide a pair of new API that can charge/uncharge a
>> resource counter until we reach a given ancestor.
>>
>> Signed-off-by: Frederic Weisbecker<fweisbec@gmail.com>
>> Acked-by: Paul Menage<paul@paulmenage.org>
>> Acked-by: Glauber Costa<glommer@parallels.com>
>> Cc: Li Zefan<lizf@cn.fujitsu.com>
>> Cc: Johannes Weiner<hannes@cmpxchg.org>
>> Cc: Aditya Kali<adityakali@google.com>
>> Cc: Oleg Nesterov<oleg@redhat.com>
>> Cc: Kay Sievers<kay.sievers@vrfy.org>
>> Cc: Tim Hockin<thockin@hockin.org>
>> Cc: Tejun Heo<htejun@gmail.com>
>> Acked-by: Kirill A. Shutemov<kirill@shutemov.name>
>> Signed-off-by: Andrew Morton<akpm@linux-foundation.org>
>
>
> Where is this function called in this series ?
>
> Thanks,
> -Kame
>
It is not... anymore!
But I forgot the patch among the "pre-requisite" patches I had.

Thanks, this can be dropped.
Re: [PATCH v2 19/29] skip memcg kmem allocations in specified code regions [message #46371 is a reply to message #46359] Wed, 16 May 2012 06:19 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
On 05/15/2012 06:46 AM, KAMEZAWA Hiroyuki wrote:
> (2012/05/12 2:44), Glauber Costa wrote:
>
>> This patch creates a mechanism that skip memcg allocations during
>> certain pieces of our core code. It basically works in the same way
>> as preempt_disable()/preempt_enable(): By marking a region under
>> which all allocations will be accounted to the root memcg.
>>
>> We need this to prevent races in early cache creation, when we
>> allocate data using caches that are not necessarily created already.
>>
>> Signed-off-by: Glauber Costa<glommer@parallels.com>
>> CC: Christoph Lameter<cl@linux.com>
>> CC: Pekka Enberg<penberg@cs.helsinki.fi>
>> CC: Michal Hocko<mhocko@suse.cz>
>> CC: Kamezawa Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com>
>> CC: Johannes Weiner<hannes@cmpxchg.org>
>> CC: Suleiman Souhlal<suleiman@google.com>
>
>
> The concept seems okay to me but...
>
>> ---
>> include/linux/sched.h | 1 +
>> mm/memcontrol.c | 25 +++++++++++++++++++++++++
>> 2 files changed, 26 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 81a173c..0501114 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1613,6 +1613,7 @@ struct task_struct {
>> unsigned long nr_pages; /* uncharged usage */
>> unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
>> } memcg_batch;
>> + atomic_t memcg_kmem_skip_account;
>
>
> If only 'current' thread touch this, you don't need to make this atomic counter.
> you can use 'long'.
>
You're absolutely right, Kame, thanks.
I first used atomic_t because I had it tested against current->mm->owner.

Do you, btw, agree to use current instead of owner here?
You can find the rationale in earlier mails between me and Suleiman.
Re: [PATCH v2 18/29] memcg: kmem controller charge/uncharge infrastructure [message #46372 is a reply to message #46360] Wed, 16 May 2012 06:42 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
On 05/15/2012 06:57 AM, KAMEZAWA Hiroyuki wrote:
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>> > +int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, s64 delta)
>> > +{
>> > + struct res_counter *fail_res;
>> > + struct mem_cgroup *_memcg;
>> > + int may_oom, ret;
>> > + bool nofail = false;
>> > +
>> > + may_oom = (gfp& __GFP_WAIT)&& (gfp& __GFP_FS)&&
>> > + !(gfp& __GFP_NORETRY);
>> > +
>> > + ret = 0;
>> > +
>> > + if (!memcg)
>> > + return ret;
>> > +
>> > + _memcg = memcg;
>> > + ret = __mem_cgroup_try_charge(NULL, gfp, delta / PAGE_SIZE,
>> > + &_memcg, may_oom);
>> > +
>> > + if ((ret == -EINTR) || (ret&& (gfp& __GFP_NOFAIL))) {
>> > + nofail = true;
>> > + /*
>> > + * __mem_cgroup_try_charge() chose to bypass to root due
>> > + * to OOM kill or fatal signal.
>> > + * Since our only options are to either fail the
>> > + * allocation or charge it to this cgroup, force the
>> > + * change, going above the limit if needed.
>> > + */
>> > + res_counter_charge_nofail(&memcg->res, delta,&fail_res);
>> > + if (do_swap_account)
>> > + res_counter_charge_nofail(&memcg->memsw, delta,
>> > + &fail_res);
>> > + } else if (ret == -ENOMEM)
>> > + return ret;
>> > +
>> > + if (nofail)
>> > + res_counter_charge_nofail(&memcg->kmem, delta,&fail_res);
>> > + else
>> > + ret = res_counter_charge(&memcg->kmem, delta,&fail_res);
>
> Ouch, you allow usage> limit ? It's BUG.
>
> IMHO, if GFP_NOFAIL, memcg accounting should be skipped. Please
>
> if (gfp_mask& __GFP_NOFAIL)
> return 0;
>
> Or avoid calling memcg_charge_kmem() you can do that as you do in patch 19/29,
> I guess you can use a trick like
>
> == in 19/29
> + if (!current->mm || atomic_read(&current->memcg_kmem_skip_account))
> + return cachep;
> +
> gfp |= cachep->allocflags;
> ==
>
> == change like this
> gfp |= cachep->allocflags;
>
> if (!current->mm || current->memcg_kmem_skip_account || gfp& __GFP_NOFAIL))
> ==
>
> Is this difficult ?
>
> Thanks,
> -Kame

Well, we disagree with that.
I actually voiced this earlier to Suleiman in the thread, but it is good
that you brought this up again - this is quite important.

I will repeat my rationale here, and if you still are not convinced,
tell me and I will be happy to switch over.

I believe that the whole reasoning behind this, is to have allocations
failing if we go over limit. If the allocation won't fail anyway, it
doesn't really matter who we charge this to.

However, if the allocation still came from a particular memcg, those
nofail allocation may prevent it to use more memory when a normal
allocation takes place.

Consider this:

limit = 4M
usage = 4M - 4k

If at this point the memcg hits a NOFAIL allocation worth 2 pages, by
the method I am using, the memcg will be at 4M + 4k after the
allocation. Charging it to the root memcg will leave it at 4M - 4k.

This means that to be able to allocate a page again, you need to free
two other pages, be it the 2 pages used by the GFP allocation or any
other. In other words: the memcg that originated the charge is held
accountable for it. If he says it can't fail for whatever reason, fine,
we respect that, but we punish it later for other allocations.

Without that GFP_NOFAIL becomes just a nice way for people to bypass
those controls altogether, since after a ton of GFP_NOFAIL allocations,
normal allocations will still succeed.

The change you propose is totally doable. I just don't believe it should
be done.

But let me know where you stand.
Re: [PATCH v2 19/29] skip memcg kmem allocations in specified code regions [message #46376 is a reply to message #46371] Wed, 16 May 2012 07:55 Go to previous messageGo to next message
KAMEZAWA Hiroyuki is currently offline  KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
Senior Member
From: *parallels.com
(2012/05/16 15:19), Glauber Costa wrote:

> On 05/15/2012 06:46 AM, KAMEZAWA Hiroyuki wrote:
>> (2012/05/12 2:44), Glauber Costa wrote:
>>
>>> This patch creates a mechanism that skip memcg allocations during
>>> certain pieces of our core code. It basically works in the same way
>>> as preempt_disable()/preempt_enable(): By marking a region under
>>> which all allocations will be accounted to the root memcg.
>>>
>>> We need this to prevent races in early cache creation, when we
>>> allocate data using caches that are not necessarily created already.
>>>
>>> Signed-off-by: Glauber Costa<glommer@parallels.com>
>>> CC: Christoph Lameter<cl@linux.com>
>>> CC: Pekka Enberg<penberg@cs.helsinki.fi>
>>> CC: Michal Hocko<mhocko@suse.cz>
>>> CC: Kamezawa Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com>
>>> CC: Johannes Weiner<hannes@cmpxchg.org>
>>> CC: Suleiman Souhlal<suleiman@google.com>
>>
>>
>> The concept seems okay to me but...
>>
>>> ---
>>> include/linux/sched.h | 1 +
>>> mm/memcontrol.c | 25 +++++++++++++++++++++++++
>>> 2 files changed, 26 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>> index 81a173c..0501114 100644
>>> --- a/include/linux/sched.h
>>> +++ b/include/linux/sched.h
>>> @@ -1613,6 +1613,7 @@ struct task_struct {
>>> unsigned long nr_pages; /* uncharged usage */
>>> unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
>>> } memcg_batch;
>>> + atomic_t memcg_kmem_skip_account;
>>
>>
>> If only 'current' thread touch this, you don't need to make this atomic counter.
>> you can use 'long'.
>>
> You're absolutely right, Kame, thanks.
> I first used atomic_t because I had it tested against current->mm->owner.
>
> Do you, btw, agree to use current instead of owner here?
> You can find the rationale in earlier mails between me and Suleiman.

I agree to use current. This information depends on the context of callers.

Thanks,
-Kame
Re: [PATCH v2 18/29] memcg: kmem controller charge/uncharge infrastructure [message #46378 is a reply to message #46372] Wed, 16 May 2012 08:18 Go to previous messageGo to next message
KAMEZAWA Hiroyuki is currently offline  KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
Senior Member
From: *parallels.com
(2012/05/16 15:42), Glauber Costa wrote:

> On 05/15/2012 06:57 AM, KAMEZAWA Hiroyuki wrote:
>>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>>>> +int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, s64 delta)
>>>> +{
>>>> + struct res_counter *fail_res;
>>>> + struct mem_cgroup *_memcg;
>>>> + int may_oom, ret;
>>>> + bool nofail = false;
>>>> +
>>>> + may_oom = (gfp& __GFP_WAIT)&& (gfp& __GFP_FS)&&
>>>> + !(gfp& __GFP_NORETRY);
>>>> +
>>>> + ret = 0;
>>>> +
>>>> + if (!memcg)
>>>> + return ret;
>>>> +
>>>> + _memcg = memcg;
>>>> + ret = __mem_cgroup_try_charge(NULL, gfp, delta / PAGE_SIZE,
>>>> + &_memcg, may_oom);
>>>> +
>>>> + if ((ret == -EINTR) || (ret&& (gfp& __GFP_NOFAIL))) {
>>>> + nofail = true;
>>>> + /*
>>>> + * __mem_cgroup_try_charge() chose to bypass to root due
>>>> + * to OOM kill or fatal signal.
>>>> + * Since our only options are to either fail the
>>>> + * allocation or charge it to this cgroup, force the
>>>> + * change, going above the limit if needed.
>>>> + */
>>>> + res_counter_charge_nofail(&memcg->res, delta,&fail_res);
>>>> + if (do_swap_account)
>>>> + res_counter_charge_nofail(&memcg->memsw, delta,
>>>> + &fail_res);
>>>> + } else if (ret == -ENOMEM)
>>>> + return ret;
>>>> +
>>>> + if (nofail)
>>>> + res_counter_charge_nofail(&memcg->kmem, delta,&fail_res);
>>>> + else
>>>> + ret = res_counter_charge(&memcg->kmem, delta,&fail_res);
>>
>> Ouch, you allow usage> limit ? It's BUG.
>>
>> IMHO, if GFP_NOFAIL, memcg accounting should be skipped. Please
>>
>> if (gfp_mask& __GFP_NOFAIL)
>> return 0;
>>
>> Or avoid calling memcg_charge_kmem() you can do that as you do in patch 19/29,
>> I guess you can use a trick like
>>
>> == in 19/29
>> + if (!current->mm || atomic_read(&current->memcg_kmem_skip_account))
>> + return cachep;
>> +
>> gfp |= cachep->allocflags;
>> ==
>>
>> == change like this
>> gfp |= cachep->allocflags;
>>
>> if (!current->mm || current->memcg_kmem_skip_account || gfp& __GFP_NOFAIL))
>> ==
>>
>> Is this difficult ?
>>
>> Thanks,
>> -Kame
>
> Well, we disagree with that.
> I actually voiced this earlier to Suleiman in the thread, but it is good
> that you brought this up again - this is quite important.
>
> I will repeat my rationale here, and if you still are not convinced,
> tell me and I will be happy to switch over.
>
> I believe that the whole reasoning behind this, is to have allocations
> failing if we go over limit. If the allocation won't fail anyway, it
> doesn't really matter who we charge this to.
>
> However, if the allocation still came from a particular memcg, those
> nofail allocation may prevent it to use more memory when a normal
> allocation takes place.
>
> Consider this:
>
> limit = 4M
> usage = 4M - 4k
>
> If at this point the memcg hits a NOFAIL allocation worth 2 pages, by
> the method I am using, the memcg will be at 4M + 4k after the
> allocation. Charging it to the root memcg will leave it at 4M - 4k.
>
> This means that to be able to allocate a page again, you need to free
> two other pages, be it the 2 pages used by the GFP allocation or any
> other. In other words: the memcg that originated the charge is held
> accountable for it. If he says it can't fail for whatever reason, fine,
> we respect that, but we punish it later for other allocations.
>

I personally think 'we punish it later' is bad thing at resource accounting.
We have 'hard limit'. It's not soft limit.

> Without that GFP_NOFAIL becomes just a nice way for people to bypass
> those controls altogether, since after a ton of GFP_NOFAIL allocations,
> normal allocations will still succeed.
>

Allowing people to bypass is not bad because they're kernel.

But, IIUC, from gfp.h
==
* __GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller
* cannot handle allocation failures. This modifier is deprecated and no new
* users should be added.
==

GFP_NOFAIL will go away and no new user is recommended.

So, please skip GFP_NOFAIL accounting and avoid to write
"usage may go over limit if you're unfortune, sorry" into memcg documentation.


> The change you propose is totally doable. I just don't believe it should
> be done.
>
> But let me know where you stand.
>

My stand point is keeping "usage <= limit" is the spec. and
important in enterprise system. So, please avoid usage > limit.

Thanks,
-Kame
Re: [PATCH v2 18/29] memcg: kmem controller charge/uncharge infrastructure [message #46379 is a reply to message #46378] Wed, 16 May 2012 08:25 Go to previous messageGo to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
On 05/16/2012 12:18 PM, KAMEZAWA Hiroyuki wrote:
>> If at this point the memcg hits a NOFAIL allocation worth 2 pages, by
>> > the method I am using, the memcg will be at 4M + 4k after the
>> > allocation. Charging it to the root memcg will leave it at 4M - 4k.
>> >
>> > This means that to be able to allocate a page again, you need to free
>> > two other pages, be it the 2 pages used by the GFP allocation or any
>> > other. In other words: the memcg that originated the charge is held
>> > accountable for it. If he says it can't fail for whatever reason, fine,
>> > we respect that, but we punish it later for other allocations.
>> >
> I personally think 'we punish it later' is bad thing at resource accounting.
> We have 'hard limit'. It's not soft limit.

That only makes sense if you will fail the allocation. If you won't, you
are over your hard limit anyway. You are just masquerading that.

>> > Without that GFP_NOFAIL becomes just a nice way for people to bypass
>> > those controls altogether, since after a ton of GFP_NOFAIL allocations,
>> > normal allocations will still succeed.
>> >
> Allowing people to bypass is not bad because they're kernel.

No, they are not. They are in process context, on behalf of a process
that belongs to a valid memcg. If they happen to be a kernel thread,
!current->mm test will send the allocation to the root memcg already.

>
> But, IIUC, from gfp.h
> ==
> * __GFP_NOFAIL: The VM implementation_must_ retry infinitely: the caller
> * cannot handle allocation failures. This modifier is deprecated and no new
> * users should be added.
> ==
>
> GFP_NOFAIL will go away and no new user is recommended.
>
Yes, I am aware of that. That's actually why I don't plan to insist on
this too much - although your e-mail didn't really convince me.

It should not matter in practice.

> So, please skip GFP_NOFAIL accounting and avoid to write
> "usage may go over limit if you're unfortune, sorry" into memcg documentation.

I won't write that, because that's not true. Is more like: "Allocations
that can fail will fail if you go over limit".

>
>> > The change you propose is totally doable. I just don't believe it should
>> > be done.
>> >
>> > But let me know where you stand.
>> >
> My stand point is keeping "usage<= limit" is the spec. and
> important in enterprise system. So, please avoid usage> limit.
>
As I said, I won't make a case here because those allocations shouldn't
matter in real life anyway. I can change it.
Re: [PATCH v2 18/29] memcg: kmem controller charge/uncharge infrastructure [message #46383 is a reply to message #46379] Wed, 16 May 2012 09:15 Go to previous messageGo to next message
KAMEZAWA Hiroyuki is currently offline  KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
Senior Member
From: *parallels.com
(2012/05/16 17:25), Glauber Costa wrote:

> On 05/16/2012 12:18 PM, KAMEZAWA Hiroyuki wrote:
>>> If at this point the memcg hits a NOFAIL allocation worth 2 pages, by
>>>> the method I am using, the memcg will be at 4M + 4k after the
>>>> allocation. Charging it to the root memcg will leave it at 4M - 4k.
>>>>
>>>> This means that to be able to allocate a page again, you need to free
>>>> two other pages, be it the 2 pages used by the GFP allocation or any
>>>> other. In other words: the memcg that originated the charge is held
>>>> accountable for it. If he says it can't fail for whatever reason, fine,
>>>> we respect that, but we punish it later for other allocations.
>>>>
>> I personally think 'we punish it later' is bad thing at resource accounting.
>> We have 'hard limit'. It's not soft limit.
>
> That only makes sense if you will fail the allocation. If you won't, you
> are over your hard limit anyway. You are just masquerading that.
>


'showing usage > limit to user' and 'avoid accounting'
is totally different user experience.



>>>> Without that GFP_NOFAIL becomes just a nice way for people to bypass
>>>> those controls altogether, since after a ton of GFP_NOFAIL allocations,
>>>> normal allocations will still succeed.
>>>>
>> Allowing people to bypass is not bad because they're kernel.
>
> No, they are not. They are in process context, on behalf of a process
> that belongs to a valid memcg. If they happen to be a kernel thread,
> !current->mm test will send the allocation to the root memcg already.
>


Yes, but it's kernel code. There will be some special reason to use __GFP_NOFAIL.

>>
>> But, IIUC, from gfp.h
>> ==
>> * __GFP_NOFAIL: The VM implementation_must_ retry infinitely: the caller
>> * cannot handle allocation failures. This modifier is deprecated and no new
>> * users should be added.
>> ==
>>
>> GFP_NOFAIL will go away and no new user is recommended.
>>
> Yes, I am aware of that. That's actually why I don't plan to insist on
> this too much - although your e-mail didn't really convince me.
>
> It should not matter in practice.
>
>> So, please skip GFP_NOFAIL accounting and avoid to write
>> "usage may go over limit if you're unfortune, sorry" into memcg documentation.
>
> I won't write that, because that's not true. Is more like: "Allocations
> that can fail will fail if you go over limit".
>

>>
>>>> The change you propose is totally doable. I just don't believe it should
>>>> be done.
>>>>
>>>> But let me know where you stand.
>>>>
>> My stand point is keeping "usage<= limit" is the spec. and
>> important in enterprise system. So, please avoid usage> limit.
>>
> As I said, I won't make a case here because those allocations shouldn't
> matter in real life anyway. I can change it.
>

My standing point is that 'usage > limit' is bug. So please avoid it if
__GFP_NOFAIL allocation is not very important.


Thanks,
-Kame
Re: [PATCH v2 02/29] slub: fix slab_state for slub [message #46400 is a reply to message #46364] Thu, 17 May 2012 10:14 Go to previous message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
On 05/16/2012 01:55 AM, David Rientjes wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>> When the slub code wants to know if the sysfs state has already been
>> initialized, it tests for slab_state == SYSFS. This is quite fragile,
>> since new state can be added in the future (it is, in fact, for
>> memcg caches). This patch fixes this behavior so the test matches
>>> = SYSFS, as all other state does.
>>
>> Signed-off-by: Glauber Costa<glommer@parallels.com>
>
> Acked-by: David Rientjes<rientjes@google.com>
>
> Can be merged now, there's no dependency on the rest of this patchset.

So, is anyone taking this? I plan another submission this week, let me
know if I should include these two patches or not.
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