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Re: [PATCH 3/4] xfs: allow assigning the tail lsn with the AIL lock held

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/4] xfs: allow assigning the tail lsn with the AIL lock held
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Wed, 21 Mar 2012 12:22:17 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20120316175636.373605151@xxxxxxxxxxxxxxxxxxxxxx>
References: <20120316175541.258282540@xxxxxxxxxxxxxxxxxxxxxx> <20120316175636.373605151@xxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 03/16/12 12:55, Christoph Hellwig wrote:
Provide a variant of xlog_assign_tail_lsn that has the AIL lock already
held.  By doing so we do an additional atomic_read + atomic_set under
the lock, which comes down to two instructions.

Switch xfs_trans_ail_update_bulk and xfs_trans_ail_delete_bulk to the
new version to reduce the number of lock roundtrips, and prepare for
a new addition that would require a third lock roundtrip in
xfs_trans_ail_delete_bulk.  This addition is also the reason for
slightly rearranging the conditionals and relying on xfs_log_space_wake
for checking that the filesystem has been shut down internally.

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

---
  fs/xfs/xfs_log.c        |   31 +++++++++++++++++++++++--------
  fs/xfs/xfs_log.h        |    1 +
  fs/xfs/xfs_trans_ail.c  |   22 +++++++++++++++-------
  fs/xfs/xfs_trans_priv.h |    1 +
  4 files changed, 40 insertions(+), 15 deletions(-)

Index: xfs/fs/xfs/xfs_log.c
===================================================================
--- xfs.orig/fs/xfs/xfs_log.c   2012-03-16 12:44:55.880363918 +0100
+++ xfs/fs/xfs/xfs_log.c        2012-03-16 12:50:24.040370003 +0100
@@ -915,27 +915,42 @@ xfs_log_need_covered(xfs_mount_t *mp)
   * We may be holding the log iclog lock upon entering this routine.
   */

Looks good.

Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>

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