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Re: Deleting files with extended attributes is dead slow

To: Bernd Schubert <bernd.schubert@xxxxxxxxxxxxxxxxxx>
Subject: Re: Deleting files with extended attributes is dead slow
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 16 Aug 2011 12:13:58 -0400
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <20110812204746.GB30615@xxxxxxxxxxxxx>
References: <j23qs9$1c3$1@xxxxxxxxxxxxxxx> <20110812204746.GB30615@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
The patch below should help with the performance of deleting files
that have external attributes.  But I still wonder why you see
attributes outside the inode if you are using 512 byte inodes and around
256k of attrs.  Can you check tat you really have external blocks for
attributes using xfs_bmap -a on the files in your workload.  Can you
also check if this goes away using 1k or 2k inode sizes?

From: Christoph Hellwig <hch@xxxxxx>
Subject: xfs: avoid synchronous transactions when deleting attr blocks

Currently xfs_attr_inactive causes a synchronous transactions if we are
removing a file that has any extents allocated to the attribute fork.  The
code looks a like a relict from the days before the busy extent list, but
with the busy extent list we avoid reusing data and attr extents that have
been freed but not commited yet, so this code is just as superflous as
the synchronous transactions for data blocks.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Index: xfs/fs/xfs/xfs_attr.c
--- xfs.orig/fs/xfs/xfs_attr.c  2011-08-15 14:31:15.485329718 -0700
+++ xfs/fs/xfs/xfs_attr.c       2011-08-15 14:31:32.025240113 -0700
@@ -823,18 +823,6 @@ xfs_attr_inactive(xfs_inode_t *dp)
        if (error)
                goto out;
-       /*
-        * Signal synchronous inactive transactions unless this is a
-        * synchronous mount filesystem in which case we know that we're here
-        * because we've been called out of xfs_inactive which means that the
-        * last reference is gone and the unlink transaction has already hit
-        * the disk so async inactive transactions are safe.
-        */
-       if (!(mp->m_flags & XFS_MOUNT_WSYNC)) {
-               if (dp->i_d.di_anextents > 0)
-                       xfs_trans_set_sync(trans);
-       }
        error = xfs_itruncate_extents(&trans, dp, XFS_ATTR_FORK, 0);
        if (error)
                goto out;
Index: xfs/fs/xfs/xfs_bmap.c
--- xfs.orig/fs/xfs/xfs_bmap.c  2011-08-15 14:33:59.801106208 -0700
+++ xfs/fs/xfs/xfs_bmap.c       2011-08-16 09:01:24.716497619 -0700
@@ -3782,19 +3782,11 @@ xfs_bmap_compute_maxlevels(
  * Routine to be called at transaction's end by xfs_bmapi, xfs_bunmapi
  * caller.  Frees all the extents that need freeing, which must be done
  * last due to locking considerations.  We never free any extents in
- * the first transaction.  This is to allow the caller to make the first
- * transaction a synchronous one so that the pointers to the data being
- * broken in this transaction will be permanent before the data is actually
- * freed.  This is necessary to prevent blocks from being reallocated
- * and written to before the free and reallocation are actually permanent.
- * We do not just make the first transaction synchronous here, because
- * there are more efficient ways to gain the same protection in some cases
- * (see the file truncation code).
+ * the first transaction.
  * Return 1 if the given transaction was committed and a new one
  * started, and 0 otherwise in the committed parameter.
 int                                            /* error */
        xfs_trans_t             **tp,           /* transaction pointer addr */

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