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Commit 00bf2560 authored by Seth Jennings's avatar Seth Jennings Committed by Greg Kroah-Hartman
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staging: zcache: remove zcache_direct_reclaim_lock 



zcache_do_preload() currently does a spin_trylock() on the
zcache_direct_reclaim_lock. Holding this lock intends to prevent
shrink_zcache_memory() from evicting zbud pages as a result
of a preload.

However, it also prevents two threads from
executing zcache_do_preload() at the same time.  The first
thread will obtain the lock and the second thread's spin_trylock()
will fail (an aborted preload) causing the page to be either lost
(cleancache) or pushed out to the swap device (frontswap). It
also doesn't ensure that the call to shrink_zcache_memory() is
on the same thread as the call to zcache_do_preload().

Additional, there is no need for this mechanism because all
zcache_do_preload() calls that come down from cleancache already
have PF_MEMALLOC set in the process flags which prevents
direct reclaim in the memory manager. If the zcache_do_preload()
call is done from the frontswap path, we _want_ reclaim to be
done (which it isn't right now).

This patch removes the zcache_direct_reclaim_lock and related
statistics in zcache.

Based on v3.1-rc8

Signed-off-by: default avatarSeth Jennings <sjenning@linux.vnet.ibm.com>
Reviewed-by: default avatarDave Hansen <dave@linux.vnet.ibm.com>
Acked-by: default avatarDan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 3b769edd

drivers/staging/zcache/zcache-main.c

+4 −27
Original line number Diff line number Diff line
@@ -962,15 +962,6 @@ int zcache_new_client(uint16_t cli_id) 
static unsigned long zcache_failed_get_free_pages;

static unsigned long zcache_failed_alloc;

static unsigned long zcache_put_to_flush;

static unsigned long zcache_aborted_preload;

static unsigned long zcache_aborted_shrink;



/*

 * Ensure that memory allocation requests in zcache don't result

 * in direct reclaim requests via the shrinker, which would cause

 * an infinite loop.  Maybe a GFP flag would be better?

 */

static DEFINE_SPINLOCK(zcache_direct_reclaim_lock);



/*

 * for now, used named slabs so can easily track usage; later can
@@ -1009,10 +1000,6 @@ static int zcache_do_preload(struct tmem_pool *pool) 
		goto out;

	if (unlikely(zcache_obj_cache == NULL))

		goto out;

	if (!spin_trylock(&zcache_direct_reclaim_lock)) {

		zcache_aborted_preload++;

		goto out;

	}

	preempt_disable();

	kp = &__get_cpu_var(zcache_preloads);

	while (kp->nr < ARRAY_SIZE(kp->objnodes)) {
@@ -1021,7 +1008,7 @@ static int zcache_do_preload(struct tmem_pool *pool) 
				ZCACHE_GFP_MASK);

		if (unlikely(objnode == NULL)) {

			zcache_failed_alloc++;

			goto unlock_out;

			goto out;

		}

		preempt_disable();

		kp = &__get_cpu_var(zcache_preloads);
@@ -1034,13 +1021,13 @@ static int zcache_do_preload(struct tmem_pool *pool) 
	obj = kmem_cache_alloc(zcache_obj_cache, ZCACHE_GFP_MASK);

	if (unlikely(obj == NULL)) {

		zcache_failed_alloc++;

		goto unlock_out;

		goto out;

	}

	page = (void *)__get_free_page(ZCACHE_GFP_MASK);

	if (unlikely(page == NULL)) {

		zcache_failed_get_free_pages++;

		kmem_cache_free(zcache_obj_cache, obj);

		goto unlock_out;

		goto out;

	}

	preempt_disable();

	kp = &__get_cpu_var(zcache_preloads);
@@ -1053,8 +1040,6 @@ static int zcache_do_preload(struct tmem_pool *pool) 
	else

		free_page((unsigned long)page);

	ret = 0;

unlock_out:

	spin_unlock(&zcache_direct_reclaim_lock);

out:

	return ret;

}
@@ -1429,8 +1414,6 @@ ZCACHE_SYSFS_RO(evicted_buddied_pages); 
ZCACHE_SYSFS_RO(failed_get_free_pages);

ZCACHE_SYSFS_RO(failed_alloc);

ZCACHE_SYSFS_RO(put_to_flush);

ZCACHE_SYSFS_RO(aborted_preload);

ZCACHE_SYSFS_RO(aborted_shrink);

ZCACHE_SYSFS_RO(compress_poor);

ZCACHE_SYSFS_RO(mean_compress_poor);

ZCACHE_SYSFS_RO_ATOMIC(zbud_curr_raw_pages);
@@ -1472,8 +1455,6 @@ static struct attribute *zcache_attrs[] = { 
	&zcache_failed_get_free_pages_attr.attr,

	&zcache_failed_alloc_attr.attr,

	&zcache_put_to_flush_attr.attr,

	&zcache_aborted_preload_attr.attr,

	&zcache_aborted_shrink_attr.attr,

	&zcache_zbud_unbuddied_list_counts_attr.attr,

	&zcache_zbud_cumul_chunk_counts_attr.attr,

	&zcache_zv_curr_dist_counts_attr.attr,
@@ -1513,11 +1494,7 @@ static int shrink_zcache_memory(struct shrinker *shrink, 
		if (!(gfp_mask & __GFP_FS))

			/* does this case really need to be skipped? */

			goto out;

		if (spin_trylock(&zcache_direct_reclaim_lock)) {

		zbud_evict_pages(nr);

			spin_unlock(&zcache_direct_reclaim_lock);

		} else

			zcache_aborted_shrink++;

	}

	ret = (int)atomic_read(&zcache_zbud_curr_raw_pages);

out: