[PATCH 1/2] super: fix calculation of shrinkable objects for small numbers

Glauber Costa
2012-12-19T08:40:17Z

The sysctl knob sysctl_vfs_cache_pressure is used to determine which
percentage of the shrinkable objects in our cache we should actively try
to shrink.

It works great in situations in which we have many objects (at least
more than 100), because the aproximation errors will be negligible. But
if this is not the case, specially when total_objects < 100, we may end
up concluding that we have no objects at all (total / 100 = 0, if total
< 100).

This is certainly not the biggest killer in the world, but may matter in
very low kernel memory situations.

Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Dave Chinner <david@fromorbit.com>
CC: "Theodore Ts'o" <tytso@mit.edu>
CC: Al Viro <viro@zeniv.linux.org.uk>
---
fs/super.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index 12f1237..660552c 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -104,7 +104,7 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
sb->s_nr_inodes_unused + fs_objects;
}

- total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure;
+ total_objects = mult_frac(total_objects, sysctl_vfs_cache_pressure, 100);
drop_super(sb);
return total_objects;
}