On Thu, 2010-07-15 at 21:46 +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Now the shrinker passes us a context, wire up a shrinker context per
> filesystem. This allows us to remove the global mount list and the
> locking problems that introduced. It also means that a shrinker call
> does not need to traverse clean filesystems before finding a
> filesystem with reclaimable inodes. This significantly reduces
> scanning overhead when lots of filesystems are present.
>
I have a comment below about an optimization you made.
It's not necessarily a bug, but I thought I'd call
attention to it anyway.
Outside of that it looks good to me.
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/linux-2.6/xfs_super.c | 2 -
> fs/xfs/linux-2.6/xfs_sync.c | 62 +++++++++--------------------------------
> fs/xfs/linux-2.6/xfs_sync.h | 2 -
> fs/xfs/xfs_mount.h | 2 +-
> 4 files changed, 15 insertions(+), 53 deletions(-)
. . .
> diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
> index be37582..f433819 100644
> --- a/fs/xfs/linux-2.6/xfs_sync.c
> +++ b/fs/xfs/linux-2.6/xfs_sync.c
> @@ -828,14 +828,7 @@ xfs_reclaim_inodes(
>
> /*
> * Shrinker infrastructure.
> - *
> - * This is all far more complex than it needs to be. It adds a global list of
> - * mounts because the shrinkers can only call a global context. We need to make
> - * the shrinkers pass a context to avoid the need for global state.
> */
> -static LIST_HEAD(xfs_mount_list);
> -static struct rw_semaphore xfs_mount_list_lock;
> -
> static int
> xfs_reclaim_inode_shrink(
> struct shrinker *shrink,
> @@ -847,65 +840,38 @@ xfs_reclaim_inode_shrink(
> xfs_agnumber_t ag;
> int reclaimable = 0;
>
> + mp = container_of(shrink, struct xfs_mount, m_inode_shrink);
> if (nr_to_scan) {
> if (!(gfp_mask & __GFP_FS))
> return -1;
>
> - down_read(&xfs_mount_list_lock);
> - list_for_each_entry(mp, &xfs_mount_list, m_mplist) {
> - xfs_inode_ag_iterator(mp, xfs_reclaim_inode, 0,
> + xfs_inode_ag_iterator(mp, xfs_reclaim_inode, 0,
> XFS_ICI_RECLAIM_TAG, 1, &nr_to_scan);
> - if (nr_to_scan <= 0)
> - break;
> - }
> - up_read(&xfs_mount_list_lock);
> - }
> + /* if we don't exhaust the scan, don't bother coming back */
> + if (nr_to_scan > 0)
> + return -1;
This short-circuit return here sort of circumvents the
SLABS_SCANNED VM event counting. On the other hand, it
seems to be counting nr_to_scan repeatedly, which isn't
necessarily that meaningful in this case either. (I
don't know how important this is.)
It also means that shrink_slab() under-counts the number
of objects freed. Again, this may not in practice be
an issue--especially since more will have actually been
freed than is claimed.
-Alex
> + }
>
> - down_read(&xfs_mount_list_lock);
> - list_for_each_entry(mp, &xfs_mount_list, m_mplist) {
> - for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
> - pag = xfs_perag_get(mp, ag);
> - reclaimable += pag->pag_ici_reclaimable;
> - xfs_perag_put(pag);
> - }
> + for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
> + pag = xfs_perag_get(mp, ag);
> + reclaimable += pag->pag_ici_reclaimable;
> + xfs_perag_put(pag);
> }
> - up_read(&xfs_mount_list_lock);
> return reclaimable;
> }
>
. . .
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