YAMAMOTO Takashi wrote:
> hi,
> 
> i implemented background reclamation for your memory controller and
> did a few benchmarks with and without it.  any comments?
> 
> YAMAMOTO Takashi
> 
> 
> -----
> "time make -j4 bzImage" in a cgroup with 64MB limit:
> 
> 	without patch:
> 		real    22m22.389s
> 		user    13m35.163s
> 		sys     6m12.283s
> 
> 		memory.failcnt after a run: 106647
> 
> 	with patch:
> 		real    19m25.860s
> 		user    14m10.549s
> 		sys     6m13.831s
> 
> 		memory.failcnt after a run: 35366
> 
> "for x in 1 2 3;do time dd if=/dev/zero bs=1M count=300|tail;done"
> in a cgroup with 16MB limit:
> 
> 	without patch:
> 		300+0 records in
> 		300+0 records out
> 		314572800 bytes (315 MB) copied, 19.0058 seconds, 16.6 MB/s
> 		u 0.00s s 0.67s e 19.01s maj 90 min 2021 in 0 out 0
> 		u 0.48s s 7.22s e 93.13s maj 20475 min 210903 in 0 out 0
> 		300+0 records in
> 		300+0 records out
> 		314572800 bytes (315 MB) copied, 14.8394 seconds, 21.2 MB/s
> 		u 0.00s s 0.63s e 14.84s maj 53 min 1392 in 0 out 0
> 		u 0.48s s 7.00s e 94.39s maj 20125 min 211145 in 0 out 0
> 		300+0 records in
> 		300+0 records out
> 		314572800 bytes (315 MB) copied, 14.0635 seconds, 22.4 MB/s
> 		u 0.01s s 0.59s e 14.07s maj 50 min 1385 in 0 out 0
> 		u 0.57s s 6.93s e 91.54s maj 20359 min 210911 in 0 out 0
> 
> 		memory.failcnt after a run: 8804
> 
> 	with patch:
> 		300+0 records in
> 		300+0 records out
> 		314572800 bytes (315 MB) copied, 5.94875 seconds, 52.9 MB/s
> 		u 0.00s s 0.67s e 5.95s maj 206 min 5393 in 0 out 0
> 		u 0.45s s 6.63s e 46.07s maj 21350 min 210252 in 0 out 0
> 		300+0 records in
> 		300+0 records out
> 		314572800 bytes (315 MB) copied, 8.16441 seconds, 38.5 MB/s
> 		u 0.00s s 0.60s e 8.17s maj 240 min 4614 in 0 out 0
> 		u 0.45s s 6.56s e 54.56s maj 22298 min 209255 in 0 out 0
> 		300+0 records in
> 		300+0 records out
> 		314572800 bytes (315 MB) copied, 4.60967 seconds, 68.2 MB/s
> 		u 0.00s s 0.60s e 4.64s maj 196 min 4733 in 0 out 0
> 		u 0.46s s 6.53s e 49.28s maj 22223 min 209384 in 0 out 0
> 
> 		memory.failcnt after a run: 1589
> -----

Results looks good.  Background reclaim will definitely help performance.
I am sure once we get the thresholds correct, the performance will improve
further.

> 
> --- linux-2.6.23-rc8-mm2-cgkswapd/mm/memcontrol.c.BACKUP	2007-10-01 17:19:57.000000000 +0900
> +++ linux-2.6.23-rc8-mm2-cgkswapd/mm/memcontrol.c	2007-10-22 13:46:01.000000000 +0900
> @@ -27,6 +27,7 @@
>  #include <linux/rcupdate.h>
>  #include <linux/swap.h>
>  #include <linux/spinlock.h>
> +#include <linux/workqueue.h>
>  #include <linux/fs.h>
> 
>  #include <asm/uaccess.h>
> @@ -63,6 +64,8 @@ struct mem_cgroup {
>  	 */
>  	spinlock_t lru_lock;
>  	unsigned long control_type;	/* control RSS or RSS+Pagecache */
> +
> +	struct work_struct reclaim_work;
>  };
> 
>  /*
> @@ -95,6 +98,9 @@ enum {
> 
>  static struct mem_cgroup init_mem_cgroup;
> 
> +static DEFINE_MUTEX(mem_cgroup_workqueue_init_lock);
> +static struct workqueue_struct *mem_cgroup_workqueue;
> +
>  static inline
>  struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
>  {
> @@ -250,6 +256,69 @@ unsigned long mem_cgroup_isolate_pages(u
>  	return nr_taken;
>  }
> 
> +static int
> +mem_cgroup_need_reclaim(struct mem_cgroup *mem)
> +{
> +	struct res_counter * const cnt = &mem->res;
> +	int doreclaim;
> +	unsigned long flags;
> +
> +	/* XXX should be in res_counter */
> +	/* XXX should not hardcode a watermark */
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	doreclaim = cnt->usage > cnt->limit / 4 * 3;
> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +
> +	return doreclaim;
> +}
> +
> +static void
> +mem_cgroup_schedule_reclaim_if_necessary(struct mem_cgroup *mem)
> +{
> +
> +	if (mem_cgroup_workqueue == NULL) {
> +		BUG_ON(mem->css.cgroup->parent != NULL);
> +		return;
> +	}
> +
> +	if (work_pending(&mem->reclaim_work))
> +		return;
> +
> +	if (!mem_cgroup_need_reclaim(mem))
> +		return;
> +
> +	css_get(&mem->css); /* XXX need some thoughts wrt cgroup removal. */
> +	/*
> +	 * XXX workqueue is not an ideal mechanism for our purpose.
> +	 * revisit later.
> +	 */
> +	if (!queue_work(mem_cgroup_workqueue, &mem->reclaim_work))
> +		css_put(&mem->css);
> +}
> +
> +static void
> +mem_cgroup_reclaim(struct work_struct *work)
> +{
> +	struct mem_cgroup * const mem =
> +	    container_of(work, struct mem_cgroup, reclaim_work);
> +	int batch_count = 128; /* XXX arbitrary */
> +
> +	for (; batch_count > 0; batch_count--) {
> +		if (!mem_cgroup_need_reclaim(mem))
> +			break;
> +		/*
> +		 * XXX try_to_free_foo is not a correct mechanism to
> +		 * use here.  eg. ALLOCSTALL counter
> +		 * revisit later.
> +		 */
> +		if (!try_to_free_mem_cgroup_pages(mem, GFP_KERNEL))
> +			break;
> +	}
> +	if (batch_count == 0)
> +		mem_cgroup_schedule_reclaim_if_necessary(mem);
> +	css_put(&mem->css);
> +}
> +
>  /*
>   * Charge the memory controller for page usage.
>   * Return
> @@ -311,6 +380,9 @@ int mem_cgroup_charge(struct page *page,
>  	 */
>  	while (res_counter_charge(&mem->res, PAGE_SIZE)) {
>  		bool is_atomic = gfp_mask & GFP_ATOMIC;
> +
> +		mem_cgroup_schedule_reclaim_if_necessary(mem);
> +
>  		/*
>  		 * We cannot reclaim under GFP_ATOMIC, fail the charge
>  		 */
> @@ -551,8 +623,18 @@ mem_cgroup_create(struct cgroup_subsys *
>  	if (unlikely((cont->parent) == NULL)) {
>  		mem = &init_mem_cgroup;
>  		init_mm.mem_cgroup = mem;
> -	} else
> +	} else {
> +		/* XXX too late for the top-level cgroup */
> +		if (mem_cgroup_workqueue == NULL) {
> +			mutex_lock(&mem_cgroup_workqueue_init_lock);
> +			if (mem_cgroup_workqueue == NULL) {
> +				mem_cgroup_workqueue =
> +				    create_workqueue("mem_cgroup");
> +			}
> +			mutex_unlock(&mem_cgroup_workqueue_init_lock);
> +		}
>  		mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
> +	}
> 
>  	if (mem == NULL)
>  		return NULL;
> @@ -562,6 +644,7 @@ mem_cgroup_create(struct cgroup_subsys *
>  	INIT_LIST_HEAD(&mem->inactive_list);
>  	spin_lock_init(&mem->lru_lock);
>  	mem->control_type = MEM_CGROUP_TYPE_ALL;
> +	INIT_WORK(&mem->reclaim_work, mem_cgroup_reclaim);
>  	return &mem->css;
>  }
> 

Can we potentially avoid direct reclaim and sleep if the charge is exceeded
and let the background reclaim do the job and wake us up?

--Vaidy

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