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xfs: don't use vfs writeback for pure metadata modifications

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Under heavy multi-way parallel create workloads, the VFS struggles
to write back all the inodes that have been changed in age order.
The bdi flusher thread becomes CPU bound, spending 85% of it's time
in the VFS code, mostly traversing the superblock dirty inode list
to separate dirty inodes old enough to flush.

We already keep an index of all metadata changes in age order - in
the AIL - and continued log pressure will do age ordered writeback
without any extra overhead at all. If there is no pressure on the
log, the xfssyncd will periodically write back metadata in ascending
disk address offset order so will be very efficient.

Hence we can stop marking VFS inodes dirty during transaction commit
or when changing timestamps during transactions. This will keep the
inodes in the superblock dirty list to those containing data or
unlogged metadata changes.

However, the timstamp changes are slightly more complex than this -
there are a couple of places that do unlogged updates of the
timestamps, and the VFS need to be informed of these. Hence add a
new function xfs_trans_ichgtime() for transactional changes,
and leave xfs_ichgtime() for the non-transactional changes.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Dave Chinner 2010-09-28 12:27:25 +10:00 • committed by Alex Elder
parent e176579e70
commit dcd79a1423
12 changed files with 65 additions and 86 deletions
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4
fs/xfs/xfs_utils.c
View file

@ -235,7 +235,7 @@ xfs_droplink(
{
int error;
xfs_ichgtime(ip, XFS_ICHGTIME_CHG);
xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);
ASSERT (ip->i_d.di_nlink > 0);
ip->i_d.di_nlink--;
@ -299,7 +299,7 @@ xfs_bumplink(
{
if (ip->i_d.di_nlink >= XFS_MAXLINK)
return XFS_ERROR(EMLINK);
xfs_ichgtime(ip, XFS_ICHGTIME_CHG);
xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);
ASSERT(ip->i_d.di_nlink > 0);
ip->i_d.di_nlink++;