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authorDave Chinner <dchinner@redhat.com>2014-05-05 17:30:15 +1000
committerDave Chinner <david@fromorbit.com>2014-05-05 17:30:15 +1000
commit3c353375761d81abfb66eb054aacceef31658e24 (patch)
tree709ca6211697a56c57dd58a21127582d581be32d /fs/xfs/xfs_dquot.h
parentf58522c5a47a1862c6b3fad97ea9285c5d68199d (diff)
downloadlinux-3c353375761d81abfb66eb054aacceef31658e24.tar.bz2
xfs: remove dquot hints
group and project quota hints are currently stored on the user dquot. If we are attaching quotas to the inode, then the group and project dquots are stored as hints on the user dquot to save having to look them up again later. The thing is, the hints are not used for that inode for the rest of the life of the inode - the dquots are attached directly to the inode itself - so the only time the hints are used is when an inode first has dquots attached. When the hints on the user dquot don't match the dquots being attache dto the inode, they are then removed and replaced with the new hints. If a user is concurrently modifying files in different group and/or project contexts, then this leads to thrashing of the hints attached to user dquot. If user quotas are not enabled, then hints are never even used. So, if the hints are used to avoid the cost of the lookup, is the cost of the lookup significant enough to justify the hint infrstructure? Maybe it was once, when there was a global quota manager shared between all XFS filesystems and was hash table based. However, lookups are now much simpler, requiring only a single lock and radix tree lookup local to the filesystem and no hash or LRU manipulations to be made. Hence the cost of lookup is much lower than when hints were implemented. Turns out that benchmarks show that, too, with thir being no differnce in performance when doing file creation workloads as a single user with user, group and project quotas enabled - the hints do not make the code go any faster. In fact, removing the hints shows a 2-3% reduction in the time it takes to create 50 million inodes.... So, let's just get rid of the hints and the complexity around them. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dave Chinner <david@fromorbit.com>
Diffstat (limited to 'fs/xfs/xfs_dquot.h')
-rw-r--r--fs/xfs/xfs_dquot.h2
1 files changed, 0 insertions, 2 deletions
diff --git a/fs/xfs/xfs_dquot.h b/fs/xfs/xfs_dquot.h
index d22ed0053c32..68a68f704837 100644
--- a/fs/xfs/xfs_dquot.h
+++ b/fs/xfs/xfs_dquot.h
@@ -52,8 +52,6 @@ typedef struct xfs_dquot {
int q_bufoffset; /* off of dq in buffer (# dquots) */
xfs_fileoff_t q_fileoffset; /* offset in quotas file */
- struct xfs_dquot*q_gdquot; /* group dquot, hint only */
- struct xfs_dquot*q_pdquot; /* project dquot, hint only */
xfs_disk_dquot_t q_core; /* actual usage & quotas */
xfs_dq_logitem_t q_logitem; /* dquot log item */
xfs_qcnt_t q_res_bcount; /* total regular nblks used+reserved */