From: Christoph Hellwig <hch@infradead.org>
To: Jens Axboe <jaxboe@fusionio.com>
Cc: linux-kernel@vger.kernel.org
Subject: merging discard request in the block layer
Date: Tue, 22 Mar 2011 15:47:55 -0400 [thread overview]
Message-ID: <20110322194755.GA20122@infradead.org> (raw)
It seems the current block layer wil happily try to merge discard
requests that were split because they are at the max that bi_size
can hold together again. At least that's what the
blk: request botched
make me believe when testing XFS code that allows multiple
asynchronous discard request, unlike the current blkdev_issue_discard
which always waits for one before starting the next.
I tried this little sniplet to prevent it:
Index: xfs/block/blk-merge.c
===================================================================
--- xfs.orig/block/blk-merge.c 2011-03-22 13:07:24.733857580 +0100
+++ xfs/block/blk-merge.c 2011-03-22 13:08:17.448856577 +0100
@@ -373,7 +373,7 @@ static int attempt_merge(struct request_
/*
* Don't merge file system requests and discard requests
*/
- if ((req->cmd_flags & REQ_DISCARD) != (next->cmd_flags & REQ_DISCARD))
+ if ((req->cmd_flags & REQ_DISCARD) || (next->cmd_flags & REQ_DISCARD))
return 0;
/*
but it has no effect. Using the big hammer and bypassing the whole
I/O schedule logic on the other works fine:
Index: xfs/block/blk-core.c
===================================================================
--- xfs.orig/block/blk-core.c 2011-03-22 13:07:24.717855861 +0100
+++ xfs/block/blk-core.c 2011-03-22 14:56:13.424856289 +0100
@@ -1218,7 +1218,7 @@ static int __make_request(struct request
spin_lock_irq(q->queue_lock);
- if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
+ if (bio->bi_rw & (REQ_FLUSH | REQ_FUA | REQ_DISCARD)) {
where = ELEVATOR_INSERT_FRONT;
goto get_rq;
}
next reply other threads:[~2011-03-22 19:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-22 19:47 Christoph Hellwig [this message]
2011-03-22 19:54 ` merging discard request in the block layer Jens Axboe
2011-03-22 21:00 ` Christoph Hellwig
2011-03-22 21:03 ` Jens Axboe
2011-03-23 13:01 ` Christoph Hellwig
2011-03-23 15:26 ` Jens Axboe
2011-03-30 14:16 ` Christoph Hellwig
2011-05-03 18:05 ` Christoph Hellwig
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