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;
}
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