From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Sandeen Date: Sun, 18 Jul 2010 04:06:32 +0000 Subject: Re: [PATCH] fix return value for mb_cache_shrink_fn when nr_to_scan Message-Id: <4C427DC8.6020504@redhat.com> List-Id: References: <4C425273.5000702@gmail.com> In-Reply-To: <4C425273.5000702@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Wang Sheng-Hui Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-mm@kvack.org, linux-ext4 , kernel-janitors , a.gruenbacher@computer.org Wang Sheng-Hui wrote: > Hi, > > 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. > I think we'd better fix the return value issue. > > Following patch is against 2.6.35-rc5. Please check it. > > you are right that it's not returning the remaining entries, but I think we can do this more simply; there isn't any reason to calculate it twice How about just moving the accounting to the end, since "count" isn't actually used when freeing, anyway.... something like this? diff --git a/fs/mbcache.c b/fs/mbcache.c index ec88ff3..3af79de 100644 --- a/fs/mbcache.c +++ b/fs/mbcache.c @@ -203,19 +203,11 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask) struct list_head *l, *ltmp; 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; - } + + spin_lock &mb_cache_spinlock); while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) { struct mb_cache_entry *ce list_entry(mb_cache_lru_list.next, @@ -229,6 +221,17 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask) e_lru_list), gfp_mask); } out: + /* Count remaining entries */ + 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); + } + spin_unlock(&mb_cache_spinlock); + return (count / 100) * sysctl_vfs_cache_pressure; }