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[PATCH] xfs: use proper interfaces for on-stack plugging

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: use proper interfaces for on-stack plugging
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 30 Mar 2011 07:05:09 -0400
Cc: jaxboe@xxxxxxxxxxxx
User-agent: Mutt/1.5.21 (2010-09-15)
Add proper blk_start_plug/blk_finish_plug pairs for the two places where
we issue buffer I/O, and remove the blk_flush_plug in xfs_buf_lock and
xfs_buf_iowait, given that context switches already flush the per-process
plugging lists.

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

Index: xfs/fs/xfs/linux-2.6/xfs_buf.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_buf.c 2011-03-29 21:55:12.863724557 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_buf.c      2011-03-29 21:58:39.028224204 +0200
@@ -919,8 +919,6 @@ xfs_buf_lock(
 
        if (atomic_read(&bp->b_pin_count) && (bp->b_flags & XBF_STALE))
                xfs_log_force(bp->b_target->bt_mount, 0);
-       if (atomic_read(&bp->b_io_remaining))
-               blk_flush_plug(current);
        down(&bp->b_sema);
        XB_SET_OWNER(bp);
 
@@ -1309,8 +1307,6 @@ xfs_buf_iowait(
 {
        trace_xfs_buf_iowait(bp, _RET_IP_);
 
-       if (atomic_read(&bp->b_io_remaining))
-               blk_flush_plug(current);
        wait_for_completion(&bp->b_iowait);
 
        trace_xfs_buf_iowait_done(bp, _RET_IP_);
@@ -1747,8 +1743,8 @@ xfsbufd(
        do {
                long    age = xfs_buf_age_centisecs * msecs_to_jiffies(10);
                long    tout = xfs_buf_timer_centisecs * msecs_to_jiffies(10);
-               int     count = 0;
                struct list_head tmp;
+               struct blk_plug plug;
 
                if (unlikely(freezing(current))) {
                        set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
@@ -1764,16 +1760,15 @@ xfsbufd(
 
                xfs_buf_delwri_split(target, &tmp, age);
                list_sort(NULL, &tmp, xfs_buf_cmp);
+
+               blk_start_plug(&plug);
                while (!list_empty(&tmp)) {
                        struct xfs_buf *bp;
                        bp = list_first_entry(&tmp, struct xfs_buf, b_list);
                        list_del_init(&bp->b_list);
                        xfs_bdstrat_cb(bp);
-                       count++;
                }
-               if (count)
-                       blk_flush_plug(current);
-
+               blk_finish_plug(&plug);
        } while (!kthread_should_stop());
 
        return 0;
@@ -1793,6 +1788,7 @@ xfs_flush_buftarg(
        int             pincount = 0;
        LIST_HEAD(tmp_list);
        LIST_HEAD(wait_list);
+       struct blk_plug plug;
 
        xfs_buf_runall_queues(xfsconvertd_workqueue);
        xfs_buf_runall_queues(xfsdatad_workqueue);
@@ -1807,6 +1803,8 @@ xfs_flush_buftarg(
         * we do that after issuing all the IO.
         */
        list_sort(NULL, &tmp_list, xfs_buf_cmp);
+
+       blk_start_plug(&plug);
        while (!list_empty(&tmp_list)) {
                bp = list_first_entry(&tmp_list, struct xfs_buf, b_list);
                ASSERT(target == bp->b_target);
@@ -1817,10 +1815,10 @@ xfs_flush_buftarg(
                }
                xfs_bdstrat_cb(bp);
        }
+       blk_finish_plug(&plug);
 
        if (wait) {
-               /* Expedite and wait for IO to complete. */
-               blk_flush_plug(current);
+               /* Wait for IO to complete. */
                while (!list_empty(&wait_list)) {
                        bp = list_first_entry(&wait_list, struct xfs_buf, 
b_list);
 

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