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Reduce contention on the vnode interlock by not acquiring the BO_LOCK

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around the check for the BV_BKGRDINPROG in the brelse() and bqrelse().
See the comment for the explanation why it is safe.

Tested by:	pho
Submitted by:	jeff
This commit is contained in:
Konstantin Belousov 2008-03-21 12:38:44 +00:00
parent 0e2c6b177f
commit e7ffdf423a
1 changed files with 10 additions and 12 deletions
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22
sys/kern/vfs_bio.c
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@ -1203,15 +1203,14 @@ brelse(struct buf *bp)
bp->b_flags &= ~B_RELBUF;
else if (vm_page_count_severe()) {
/*
* XXX This lock may not be necessary since BKGRDINPROG
* cannot be set while we hold the buf lock, it can only be
* cleared if it is already pending.
* The locking of the BO_LOCK is not necessary since
* BKGRDINPROG cannot be set while we hold the buf
* lock, it can only be cleared if it is already
* pending.
*/
if (bp->b_vp) {
BO_LOCK(bp->b_bufobj);
if (!(bp->b_vflags & BV_BKGRDINPROG))
bp->b_flags |= B_RELBUF;
BO_UNLOCK(bp->b_bufobj);
} else
bp->b_flags |= B_RELBUF;
}
@ -1465,13 +1464,13 @@ bqrelse(struct buf *bp)
TAILQ_INSERT_TAIL(&bufqueues[bp->b_qindex], bp, b_freelist);
} else {
/*
* XXX This lock may not be necessary since BKGRDINPROG
* cannot be set while we hold the buf lock, it can only be
* cleared if it is already pending.
* The locking of the BO_LOCK for checking of the
* BV_BKGRDINPROG is not necessary since the
* BV_BKGRDINPROG cannot be set while we hold the buf
* lock, it can only be cleared if it is already
* pending.
*/
BO_LOCK(bp->b_bufobj);
if (!vm_page_count_severe() || bp->b_vflags & BV_BKGRDINPROG) {
BO_UNLOCK(bp->b_bufobj);
if (!vm_page_count_severe() || (bp->b_vflags & BV_BKGRDINPROG)) {
bp->b_qindex = QUEUE_CLEAN;
TAILQ_INSERT_TAIL(&bufqueues[QUEUE_CLEAN], bp,
b_freelist);
@ -1481,7 +1480,6 @@ bqrelse(struct buf *bp)
* the buffer (most importantly: the wired pages
* making up its backing store) *now*.
*/
BO_UNLOCK(bp->b_bufobj);
mtx_unlock(&bqlock);
brelse(bp);
return;