Messages in this thread | | | Date | Wed, 23 Jun 2010 12:40:46 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] block: Don't count_vm_events for discard bio in submit_bio. |
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On Wed, 23 Jun 2010 11:24:51 +0800 Tao Ma <tao.ma@oracle.com> wrote:
> In submit_bio, we count vm events by check READ/WRITE. > But actually DISCARD_NOBARRIER also has the WRITE flag set. > It looks as if in blkdev_issue_discard, we also add a > page as the payload and the bio_has_data check isn't enough. > So add another check for discard bio. > > Cc: Jens Axboe <axboe@kernel.dk> > Signed-off-by: Tao Ma <tao.ma@oracle.com> > --- > block/blk-core.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index f84cce4..a725602 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1586,7 +1586,7 @@ void submit_bio(int rw, struct bio *bio) > * If it's a regular read/write or a barrier with data attached, > * go through the normal accounting stuff before submission. > */ > - if (bio_has_data(bio)) { > + if (bio_has_data(bio) && !(rw & BIO_RW_DISCARD)) { > if (rw & WRITE) { > count_vm_events(PGPGOUT, count); > } else {
Yes, that's a buglet.
Note that Christoph's "[PATCH, RFC] block: don't allocate a payload for discard request" will fix it in a better way. That patch is in linux-next now, but I expect it will be taken out again (quickly, please) because Mike has found a number of problems with it.
Your patch looks like a decent temporary fix for mainline, and a permanent one for -stable.
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