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Date: Mon, 30 Jul 2012 08:40:11 +0800 From: majianpeng <majianpeng@...il.com> To: "Jeff Moyer" <jmoyer@...hat.com> Cc: viro <viro@...IV.linux.org.uk>, "Neil Brown" <neilb@...e.de>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org>, linux-raid <linux-raid@...r.kernel.org> Subject: Re: Re: [RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio. On 2012-07-27 22:21 Jeff Moyer <jmoyer@...hat.com> Wrote: >majianpeng <majianpeng@...il.com> writes: > >> When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page, >> it will use bi_rw. >> Fox example, in functiion __bio_add_page,it will call merge_bvec_fn(). >> The merge_bvec_fn of raid456 will use the bi_rw to judge the merge. >>>> if ((bvm->bi_rw & 1) == WRITE) >>>> return biovec->bv_len; /* always allow writes to be mergeable */ >> >> Signed-off-by: Jianpeng Ma <majianpeng@...il.com> > >Good catch. How did you find this? Did you experience data corruption >as a result of this oversight, reduced performance due to missed merge >opportunities, or did you just notice it in reviewing the code? > >Reviewed-by: Jeff Moyer <jmoyer@...hat.com> > Sorry for late to reply. When i analysed the performance of raid5, i found this bug. >> >> There are many place like this in kernel.If you think this patch ok, i will correct those. >> --- >> fs/direct-io.c | 1 + >> 1 files changed, 1 insertions(+), 0 deletions(-) >> >> diff --git a/fs/direct-io.c b/fs/direct-io.c >> index 1faf4cb..77f0bbf 100644 >> --- a/fs/direct-io.c >> +++ b/fs/direct-io.c >> @@ -349,6 +349,7 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio, >> >> bio->bi_bdev = bdev; >> bio->bi_sector = first_sector; >> + bio->bi_rw = dio->rw; >> if (dio->is_async) >> bio->bi_end_io = dio_bio_end_aio; >> else
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