[XFS] Radix tree based inode caching

One of the perpetual scaling problems XFS has is indexing it's incore
inodes. We currently uses hashes and the default hash sizes chosen can
only ever be a tradeoff between memory consumption and the maximum
realistic size of the cache.

As a result, anyone who has millions of inodes cached on a filesystem
needs to tunes the size of the cache via the ihashsize mount option to
allow decent scalability with inode cache operations.

A further problem is the separate inode cluster hash, whose size is based
on the ihashsize but is smaller, and so under certain conditions (sparse
cluster cache population) this can become a limitation long before the
inode hash is causing issues.

The following patchset removes the inode hash and cluster hash and
replaces them with radix trees to avoid the scalability limitations of the
hashes. It also reduces the size of the inodes by 3 pointers....

SGI-PV: 969561
SGI-Modid: xfs-linux-melb:xfs-kern:29481a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index 51c09c114a20..9381b0360c4b 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -197,6 +197,10 @@ typedef struct xfs_perag
 #endif
         xfs_perag_busy_t *pagb_list;    /* unstable blocks */
         atomic_t        pagf_fstrms;    /* # of filestreams active in this AG */
+
+        int             pag_ici_init;   /* incore inode cache initialised */
+        rwlock_t        pag_ici_lock;   /* incore inode lock */
+        struct radix_tree_root pag_ici_root;    /* incore inode cache root */
 } xfs_perag_t;
 
 #define XFS_AG_MAXLEVELS(mp)            ((mp)->m_ag_maxlevels)