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Subject[PATCH] staging: zcache: remove zcache_direct_reclaim_lock
Date
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: Seth Jennings <sjenning@linux.vnet.ibm.com>
Reviewed-by: Dave Hansen <dave@linux.vnet.ibm.com>
---
drivers/staging/zcache/zcache-main.c | 31 ++++---------------------------
1 files changed, 4 insertions(+), 27 deletions(-)

diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 462fbc2..a61b267 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -962,15 +962,6 @@ out:
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;
}
@@ -1423,8 +1408,6 @@ 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);
@@ -1466,8 +1449,6 @@ 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,
@@ -1507,11 +1488,7 @@ 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++;
+ zbud_evict_pages(nr);
}
ret = (int)atomic_read(&zcache_zbud_curr_raw_pages);
out:
--
1.7.4.1


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