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[PATCH v3 02/13] memcg: Reclaim when more than one page needed. [message #47883] Tue, 18 September 2012 14:03 Go to next message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
From: *parallels.com
From: Suleiman Souhlal <ssouhlal@FreeBSD.org>

mem_cgroup_do_charge() was written before kmem accounting, and expects
three cases: being called for 1 page, being called for a stock of 32
pages, or being called for a hugepage. If we call for 2 or 3 pages (and
both the stack and several slabs used in process creation are such, at
least with the debug options I had), it assumed it's being called for
stock and just retried without reclaiming.

Fix that by passing down a minsize argument in addition to the csize.

And what to do about that (csize == PAGE_SIZE && ret) retry? If it's
needed at all (and presumably is since it's there, perhaps to handle
races), then it should be extended to more than PAGE_SIZE, yet how far?
And should there be a retry count limit, of what? For now retry up to
COSTLY_ORDER (as page_alloc.c does) and make sure not to do it if
__GFP_NORETRY.

[v4: fixed nr pages calculation pointed out by Christoph Lameter ]

Signed-off-by: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Glauber Costa <glommer@parallels.com>
Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
---
mm/memcontrol.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9d3bc72..b12121b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2232,7 +2232,8 @@ enum {
};

static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
- unsigned int nr_pages, bool oom_check)
+ unsigned int nr_pages, unsigned int min_pages,
+ bool oom_check)
{
unsigned long csize = nr_pages * PAGE_SIZE;
struct mem_cgroup *mem_over_limit;
@@ -2255,18 +2256,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
} else
mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
/*
- * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
- * of regular pages (CHARGE_BATCH), or a single regular page (1).
- *
* Never reclaim on behalf of optional batching, retry with a
* single page instead.
*/
- if (nr_pages == CHARGE_BATCH)
+ if (nr_pages > min_pages)
return CHARGE_RETRY;

if (!(gfp_mask & __GFP_WAIT))
return CHARGE_WOULDBLOCK;

+ if (gfp_mask & __GFP_NORETRY)
+ return CHARGE_NOMEM;
+
ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
return CHARGE_RETRY;
@@ -2279,7 +2280,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
* unlikely to succeed so close to the limit, and we fall back
* to regular pages anyway in case of failure.
*/
- if (nr_pages == 1 && ret)
+ if (nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER) && ret)
return CHARGE_RETRY;

/*
@@ -2414,7 +2415,8 @@ again:
nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
}

- ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check);
+ ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, nr_pages,
+ oom_check);
switch (ret) {
case CHARGE_OK:
break;
--
1.7.11.4
Re: [PATCH v3 02/13] memcg: Reclaim when more than one page needed. [message #48179 is a reply to message #47883] Mon, 01 October 2012 19:00 Go to previous message
Johannes Weiner is currently offline  Johannes Weiner
Messages: 9
Registered: November 2010
Junior Member
From: *parallels.com
On Tue, Sep 18, 2012 at 06:03:59PM +0400, Glauber Costa wrote:
> From: Suleiman Souhlal <ssouhlal@FreeBSD.org>
>
> mem_cgroup_do_charge() was written before kmem accounting, and expects
> three cases: being called for 1 page, being called for a stock of 32
> pages, or being called for a hugepage. If we call for 2 or 3 pages (and
> both the stack and several slabs used in process creation are such, at
> least with the debug options I had), it assumed it's being called for
> stock and just retried without reclaiming.
>
> Fix that by passing down a minsize argument in addition to the csize.
>
> And what to do about that (csize == PAGE_SIZE && ret) retry? If it's

Wow, that patch set has been around for a while. It's been nr_pages
== 1 for a while now :-)

> needed at all (and presumably is since it's there, perhaps to handle
> races), then it should be extended to more than PAGE_SIZE, yet how far?
> And should there be a retry count limit, of what? For now retry up to
> COSTLY_ORDER (as page_alloc.c does) and make sure not to do it if
> __GFP_NORETRY.
>
> [v4: fixed nr pages calculation pointed out by Christoph Lameter ]
>
> Signed-off-by: Suleiman Souhlal <suleiman@google.com>
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Acked-by: Michal Hocko <mhocko@suse.cz>
> ---
> mm/memcontrol.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 9d3bc72..b12121b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2232,7 +2232,8 @@ enum {
> };
>
> static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> - unsigned int nr_pages, bool oom_check)
> + unsigned int nr_pages, unsigned int min_pages,
> + bool oom_check)

I'm not a big fan of the parameter names. Can we make this function
officially aware of batching and name the parameters like the
arguments that are passed in? I.e. @batch and @nr_pages?

> {
> unsigned long csize = nr_pages * PAGE_SIZE;
> struct mem_cgroup *mem_over_limit;
> @@ -2255,18 +2256,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> } else
> mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
> /*
> - * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
> - * of regular pages (CHARGE_BATCH), or a single regular page (1).
> - *
> * Never reclaim on behalf of optional batching, retry with a
> * single page instead.

"[...] with the amount of actually required pages instead."

> */
> - if (nr_pages == CHARGE_BATCH)
> + if (nr_pages > min_pages)
> return CHARGE_RETRY;

if (batch > nr_pages)
return CHARGE_RETRY;

But that is all just nitpicking. Functionally, it looks sane, so:

Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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