lkml.org 
[lkml]   [2011]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: merging discard request in the block layer
On 2011-03-22 20:47, Christoph Hellwig wrote:
> 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

That would seem to indicate a bug in the merging logic instead.

> 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;
>
> /*

That's not going to be enough, you want to disable the bio to request
merging of discards as well in elevator.c:elv_rq_merge_ok(). Does
that then fix it?


--
Jens Axboe



\
 
 \ /
  Last update: 2011-03-22 20:57    [W:0.107 / U:0.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site