From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: [RFC PATCH] raid5: Add R5_ReadNoMerge flag which prevent bio from merging at block layer Date: Tue, 3 Jul 2012 16:38:10 +1000 Message-ID: <20120703163810.531a000c@notabene.brown> References: <201207031423377650880@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/0bGb9at4zO8lflMAOY1kowI"; protocol="application/pgp-signature" Return-path: In-Reply-To: <201207031423377650880@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: majianpeng Cc: linux-raid , axboe List-Id: linux-raid.ids --Sig_/0bGb9at4zO8lflMAOY1kowI Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Tue, 3 Jul 2012 14:23:41 +0800 majianpeng wrote: > Because bios will merge at block-layer,so bios-error may caused by other > bio which be merged into to the same request. > Using this flag,it will find exactly error-sector and not do redundant > operation like re-write and re-read. >=20 > Signed-off-by: majianpeng Hi, I think this patch needs a more detailed explanation. What exactly is the situation that causes a problem, and what exactly is the problem that it causes? Pretend that I don't know anything about what happens below the md level.. Thanks, NeilBrown > --- > block/blk-core.c | 8 ++++++++ > drivers/md/raid5.c | 16 +++++++++++++--- > drivers/md/raid5.h | 1 + > 3 files changed, 22 insertions(+), 3 deletions(-) >=20 > diff --git a/block/blk-core.c b/block/blk-core.c > index 3c923a7..ee04bfc 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1401,6 +1401,9 @@ void init_request_from_bio(struct request *req, str= uct bio *bio) > if (bio->bi_rw & REQ_RAHEAD) > req->cmd_flags |=3D REQ_FAILFAST_MASK; > =20 > + if (unlikely(bio->bi_rw & REQ_NOMERGE)) > + req->cmd_flags |=3D REQ_NOMERGE; > + > req->errors =3D 0; > req->__sector =3D bio->bi_sector; > req->ioprio =3D bio_prio(bio); > @@ -1428,6 +1431,11 @@ void blk_queue_bio(struct request_queue *q, struct= bio *bio) > goto get_rq; > } > =20 > + if (unlikely(bio->bi_rw & REQ_NOMERGE)) { > + spin_lock_irq(q->queue_lock); > + where =3D ELEVATOR_INSERT_BACK; > + goto get_rq; > + } > /* > * Check if we can merge with the plugged list before grabbing > * any locks. > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c > index d267672..04f78d2 100644 > --- a/drivers/md/raid5.c > +++ b/drivers/md/raid5.c > @@ -632,6 +632,9 @@ static void ops_run_io(struct stripe_head *sh, struct= stripe_head_state *s) > else > bi->bi_sector =3D (sh->sector > + rdev->data_offset); > + if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags)) > + bi->bi_rw |=3D REQ_NOMERGE; > + > bi->bi_flags =3D 1 << BIO_UPTODATE; > bi->bi_idx =3D 0; > bi->bi_io_vec[0].bv_len =3D STRIPE_SIZE; > @@ -1731,7 +1734,9 @@ static void raid5_end_read_request(struct bio * bi,= int error) > atomic_add(STRIPE_SECTORS, &rdev->corrected_errors); > clear_bit(R5_ReadError, &sh->dev[i].flags); > clear_bit(R5_ReWrite, &sh->dev[i].flags); > - } > + } else if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags)) > + clear_bit(R5_ReadNoMerge, &sh->dev[i].flags); > + > if (atomic_read(&rdev->read_errors)) > atomic_set(&rdev->read_errors, 0); > } else { > @@ -1773,7 +1778,11 @@ static void raid5_end_read_request(struct bio * bi= , int error) > else > retry =3D 1; > if (retry) > - set_bit(R5_ReadError, &sh->dev[i].flags); > + if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags)) { > + set_bit(R5_ReadError, &sh->dev[i].flags); > + clear_bit(R5_ReadNoMerge, &sh->dev[i].flags); > + } else > + set_bit(R5_ReadNoMerge, &sh->dev[i].flags); > else { > clear_bit(R5_ReadError, &sh->dev[i].flags); > clear_bit(R5_ReWrite, &sh->dev[i].flags); > @@ -4481,7 +4490,8 @@ static int retry_aligned_read(struct r5conf *conf,= struct bio *raid_bio) > conf->retry_read_aligned =3D raid_bio; > return handled; > } > - > + if (likely(raid_bio->bi_size >> 9) > STRIPE_SECTORS) > + set_bit(R5_ReadNoMerge, &sh->dev[dd_idx].flags); > handle_stripe(sh); > release_stripe(sh); > handled++; > diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h > index 2164021..6767d07 100644 > --- a/drivers/md/raid5.h > +++ b/drivers/md/raid5.h > @@ -273,6 +273,7 @@ enum r5dev_flags { > R5_Wantwrite, > R5_Overlap, /* There is a pending overlapping request > * on this block */ > + R5_ReadNoMerge, /* prevent bio from merging in block-layer */ > R5_ReadError, /* seen a read error here recently */ > R5_ReWrite, /* have tried to over-write the readerror */ > =20 --Sig_/0bGb9at4zO8lflMAOY1kowI Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQIVAwUBT/KTUjnsnt1WYoG5AQL/kw//TxdUYfx7W4VkAHcMDACDwiEwyBIlfAiw 9AC0kmHqbim2PdvyYpSe5BG6A2CfN8EG2w6Q0VqgfP/rH4WPcnTggZdccmZ4kkTM NV/a7aePJmy0CMZg1z5YTaN1Ds/Q2pL6ukyA5QXPBTb4/wuU/+pGuIQD6+Q3A/iq hbK3g9Ym8/0GMmgacog3mAyOfXYBQnMi01m7iSItrsImgmgbNA3v0Z8LUg2noyR4 SNrp0eZMBtD24ccPvq8dgqz7+11f3TVKfVGlbhuWhgqxAGPgg9SuyrLp6lhEaPfS gjh1B2ijOGcU9UtyTNwvZVWSRiGzy9HTG9OpWpoRirCetPc0443itYSkBdhzGR7Z GPW+5VeM2N0hn/wWLT2kO2Xyn8HRPQzxuMahPRIjS+317U4BdGFK8CrXMBw305K8 5sxj3KeLQM5E2aCIHn9LIrR+U3BJokvi3sE/RY9knXRMP0XMjcEF3BmMnyRAZGpF Zx9XtBnu27SC8S8ra8mzVRVEVlNFw5qbnBOhvDYW4YMV9FLq8Vt8h7W+1KJ5SHvA punt2PLwodJmYkTXuP4UFednLokR5i1jj3P0cn9+uSKfxASyWAO8OsirPlsWZAU1 U0fpo5/YK4g8wuI1N/1j5977gwZOayQhK/b3E/NSpaKfqQB3TjOv+e4qhuIZBbic mkiKoAv8ysQ= =oVpy -----END PGP SIGNATURE----- --Sig_/0bGb9at4zO8lflMAOY1kowI--