linux-ext4 - [PATCH 1/2 RESEND] fix return value for mb_cache_shrink_fn when nr_to

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Date:	Sun, 18 Jul 2010 21:57:04 +0800
From:	Wang Sheng-Hui <crosslonelyover@...il.com>
To:	linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
	linux-mm@...ck.org, linux-ext4 <linux-ext4@...r.kernel.org>,
	kernel-janitors <kernel-janitors@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Eric Sandeen <sandeen@...hat.com>
Subject: [PATCH 1/2 RESEND] fix return value for mb_cache_shrink_fn when nr_to_scan
 > 0

Sorry to resend this patch. For the 2nd patch should
be applied after this patch, I just send them together.

Following is the explanation of the patch:
The comment for struct shrinker in include/linux/mm.h says
"shrink...It should return the number of objects which remain in the
cache."
Please notice the word "remain".

In fs/mbcache.h, mb_cache_shrink_fn is used as the shrink function:
       static struct shrinker mb_cache_shrinker = {
               .shrink = mb_cache_shrink_fn,
               .seeks = DEFAULT_SEEKS,
       };
In mb_cache_shrink_fn, the return value for nr_to_scan > 0 is the
number of mb_cache_entry before shrink operation. It may because the
memory usage for mbcache is low, so the effect is not so obvious.

Per Eric Sandeen, we should do the counting only once.
Per Christoph Hellwig, we should use list_for_each_entry instead of
list_for_each here.

Following patch is against 2.6.35-rc4. Please check it.


Signed-off-by: Wang Sheng-Hui <crosslonelyover@...il.com>
---
 fs/mbcache.c |   22 +++++++++++-----------
 1 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/fs/mbcache.c b/fs/mbcache.c
index ec88ff3..5697d9e 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -201,21 +201,13 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask)
 {
 	LIST_HEAD(free_list);
 	struct list_head *l, *ltmp;
+	struct mb_cache *cache;
 	int count = 0;

-	spin_lock(&mb_cache_spinlock);
-	list_for_each(l, &mb_cache_list) {
-		struct mb_cache *cache =
-			list_entry(l, struct mb_cache, c_cache_list);
-		mb_debug("cache %s (%d)", cache->c_name,
-			  atomic_read(&cache->c_entry_count));
-		count += atomic_read(&cache->c_entry_count);
-	}
 	mb_debug("trying to free %d entries", nr_to_scan);
-	if (nr_to_scan == 0) {
-		spin_unlock(&mb_cache_spinlock);
+	if (nr_to_scan == 0)
 		goto out;
-	}
+
 	while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) {
 		struct mb_cache_entry *ce =
 			list_entry(mb_cache_lru_list.next,
@@ -229,6 +221,14 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask)
 						   e_lru_list), gfp_mask);
 	}
 out:
+	spin_lock(&mb_cache_spinlock);
+	list_for_each_entry(cache, &mb_cache_list, c_cache_list) {
+		mb_debug("cache %s (%d)", cache->c_name,
+			  atomic_read(&cache->c_entry_count));
+		count += atomic_read(&cache->c_entry_count);
+	}
+	spin_unlock(&mb_cache_spinlock);
+
 	return (count / 100) * sysctl_vfs_cache_pressure;
 }

-- 
1.7.1.1




-- 
Thanks and Regards,
shenghui
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