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

Glauber Costa
2012-12-20T10:59:14Z

On 12/20/2012 11:06 AM, Dave Chinner wrote:
> On Wed, Dec 19, 2012 at 12:40:17PM +0400, Glauber Costa wrote:
>> 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;
>
> Hi Glauber,
>
> sysctl_vfs_cache_pressure all over the place with exactly the same
> calculation. Can you fix all of them in one pass?
>

affirmative, sir!