On Wed 23-01-13 01:06:08, Ted Tso wrote:
> The VFS's prune_super() function allows for the file system to prune
> file-system specific objects. Ext4 would like to use this to prune
> parts of the inode's extent cache. The object lifetime rules used by
> ext4 is somewhat different from the those of the dentry and inode in
> the VFS. Ext4's extent cache objects can be pruned without removing
> the inode; however if an inode is pruned, all of the extent cache
> objects associated with the inode are immediately removed.
>
> To accomodate this rule, we measure the number of fs-specific objects
> before the dentry and inodes are pruned, and then measure them again
> afterwards. If the number of fs-specific objects have decreased, we
> credit that decrease as part of the shrink operation, so that we do
> not end up removing too many fs-specific objects.
>
> In the case where fs-specific objects are not removed when inodes are
> removed, this will not change the behavior of prune_super() in any
> appreciable way. (Currently the only other user of this facility is
> XFS, and this change should not affect XFS's usage of this facility
> for this reason.)
The patch looks good to me. So you can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
I've also added Dave to CC.
Honza
>
> Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> ---
> fs/super.c | 22 +++++++++++++++++++---
> 1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/fs/super.c b/fs/super.c
> index 12f1237..fb57bd2 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -80,6 +80,7 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> if (sc->nr_to_scan) {
> int dentries;
> int inodes;
> + int fs_to_scan = 0;
>
> /* proportion the scan between the caches */
> dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
> @@ -87,7 +88,7 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
> total_objects;
> if (fs_objects)
> - fs_objects = (sc->nr_to_scan * fs_objects) /
> + fs_to_scan = (sc->nr_to_scan * fs_objects) /
> total_objects;
> /*
> * prune the dcache first as the icache is pinned by it, then
> @@ -96,8 +97,23 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
> prune_dcache_sb(sb, dentries);
> prune_icache_sb(sb, inodes);
>
> - if (fs_objects && sb->s_op->free_cached_objects) {
> - sb->s_op->free_cached_objects(sb, fs_objects);
> + /*
> + * If as a result of pruning the icache, we released some
> + * of the fs_objects, give credit to the fact and
> + * reduce the number of fs objects that we should try
> + * to release.
> + */
> + if (fs_to_scan) {
> + int fs_objects_now = sb->s_op->nr_cached_objects(sb);
> +
> + if (fs_objects_now < fs_objects)
> + fs_to_scan -= fs_objects - fs_objects_now;
> + if (fs_to_scan < 0)
> + fs_to_scan = 0;
> + }
> +
> + if (fs_to_scan && sb->s_op->free_cached_objects) {
> + sb->s_op->free_cached_objects(sb, fs_to_scan);
> fs_objects = sb->s_op->nr_cached_objects(sb);
> }
> total_objects = sb->s_nr_dentry_unused +
> --
> 1.7.12.rc0.22.gcdd159b
>
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--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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