On Thu, 2013-08-29 at 00:19 +0300, Kirill A. Shutemov wrote:
> > ---
> > fs/super.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/fs/super.c b/fs/super.c
> > index 68307c0..70fa26c 100644
> > --- a/fs/super.c
> > +++ b/fs/super.c
> > @@ -53,6 +53,7 @@ static char *sb_writers_name[SB_FREEZE_LEVELS] = {
> > * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
> > * take a passive reference to the superblock to avoid this from occurring.
> > */
> > +#define SB_CACHE_LOW 5
> > static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> > {
> > struct super_block *sb;
> > @@ -68,6 +69,13 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> > if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
> > return -1;
> >
> > + /*
> > + * Don't prune if we have few cached objects to reclaim to
> > + * avoid useless sb_lock contention
> > + */
> > + if ((sb->s_nr_dentry_unused + sb->s_nr_inodes_unused) <= SB_CACHE_LOW)
> > + return -1;
>
> I don't think it's correct: you don't account fs_objects here and
> prune_icache_sb() calls invalidate_mapping_pages() which can free a lot of
> memory. It's too naive approach. You can miss a memory hog easily this
> way.
Is it safe to compute sb->s_op->nr_cached_objects(sb), assuming non null
s_op without holding sb_lock to increment ref count on sb?
I think it is safe as we hold the shrinker_rwsem so we cannot
unregister the shrinker and the s_op and sb
structure should still be there. However, I'm not totally sure.
Tim
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
---
diff --git a/fs/super.c b/fs/super.c
index 68307c0..173d0d9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -53,6 +53,7 @@ static char *sb_writers_name[SB_FREEZE_LEVELS] = {
* shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
* take a passive reference to the superblock to avoid this from occurring.
*/
+#define SB_CACHE_LOW 5
static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
{
struct super_block *sb;
@@ -68,6 +69,17 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
return -1;
+ total_objects = sb->s_nr_dentry_unused + sb->s_nr_inodes_unused;
+ if (sb->s_op && sb->s_op->nr_cached_objects)
+ total_objects += sb->s_op->nr_cached_objects(sb);
+
+ /*
+ * Don't prune if we have few cached objects to reclaim to
+ * avoid useless sb_lock contention
+ */
+ if (total_objects <= SB_CACHE_LOW)
+ return -1;
+
if (!grab_super_passive(sb))
return -1;
--
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