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From: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
To: "hch@infradead.org" <hch@infradead.org>,
	"Martin K. Petersen" <martin.petersen@oracle.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>,
	Kirill Tkhai <ktkhai@virtuozzo.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>,
	"bob.liu@oracle.com" <bob.liu@oracle.com>,
	"agk@redhat.com" <agk@redhat.com>,
	"snitzer@redhat.com" <snitzer@redhat.com>,
	"dm-devel@redhat.com" <dm-devel@redhat.com>,
	"song@kernel.org" <song@kernel.org>,
	"tytso@mit.edu" <tytso@mit.edu>,
	"adilger.kernel@dilger.ca" <adilger.kernel@dilger.ca>,
	"ming.lei@redhat.com" <ming.lei@redhat.com>,
	"osandov@fb.com" <osandov@fb.com>,
	"jthumshirn@suse.de" <jthumshirn@suse.de>,
	"minwoo.im.dev@gmail.com" <minwoo.im.dev@gmail.com>,
	Damien Le Moal <Damien.LeMoal@wdc.com>,
	"andrea.parri@amarulasolutions.com" 
	<andrea.parri@amarulasolutions.com>,
	"hare@suse.com" <hare@suse.com>, "tj@kernel.org" <tj@kernel.org>,
	Ajay Joshi <Ajay.Joshi@wdc.com>,
	"sagi@grimberg.me" <sagi@grimberg.me>,
	"dsterba@suse.com" <dsterba@suse.com>,
	"bvanassche@acm.org" <bvanassche@acm.org>,
	"dhowells@redhat.com" <dhowells@redhat.com>,
	"asml.silence@gmail.com" <asml.silence@gmail.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v7 0/6] block: Introduce REQ_ALLOCATE flag for REQ_OP_WRITE_ZEROES
Date: Thu, 26 Mar 2020 16:48:08 +0000
Message-ID: <BYAPR04MB4965C03A4E397333E5141B9086CF0@BYAPR04MB4965.namprd04.prod.outlook.com> (raw)
In-Reply-To: <20200326144556.GA4317@infradead.org>

On 03/26/2020 07:46 AM, Christoph Hellwig wrote:
> On Thu, Mar 26, 2020 at 10:34:42AM -0400, Martin K. Petersen wrote:
>>> I just worry about the proliferation of identical merging and
>>> splitting code throughout the block stack as we add additional
>>> single-range, no payload operations (Verify, etc.). I prefer to
>>> enforce the semantics in the LLD and not in the plumbing. But I
>>> won't object to a separate REQ_OP_ALLOCATE if you find the
>>> resulting code duplication acceptable.
> I find it acceptable for now.  And I think we should find some way
> (e.g. by being table driven) to share code between differnet
> opcodes.
>

With reference to Martin's comment (verify etc) there is a significant
advantage when using payloadless bio to offload the functionality
to the directly attached device and over the fabrics when dealing
with larger disks.

How about we create a helper which is independent of the operations
can accept req_op and issues the payloadless bios. Something like
following totally untested :-

diff --git a/block/blk-lib.c b/block/blk-lib.c
index cf9e75a730b4..d3fccd3211cc 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -209,6 +209,33 @@ int blkdev_issue_write_same(struct block_device
*bdev, sector_t sector,
  }
  EXPORT_SYMBOL(blkdev_issue_write_same);

+static void __blkdev_issue_payloadless(struct block_device *bdev,
unsigned op,
+               sector_t sector, sector_t nr_sects, gfp_t gfp_mask,
+               struct bio **biop, unsigned bio_opf, unsigned int
max_sectors)
+{
+       struct bio *bio = *biop;
+
+       while (nr_sects) {
+               bio = blk_next_bio(bio, 0, gfp_mask);
+               bio->bi_iter.bi_sector = sector;
+               bio_set_dev(bio, bdev);
+               bio->bi_opf = op;
+               bio->bi_opf |= bio_opf;
+
+               if (nr_sects > max_sectors) {
+                       bio->bi_iter.bi_size = max_sectors << 9;
+                       nr_sects -= max_sectors;
+                       sector += max_sectors;
+               } else {
+                       bio->bi_iter.bi_size = nr_sects << 9;
+                       nr_sects = 0;
+               }
+               cond_resched();
+       }
+
+       *biop = bio;
+}
+
  static int __blkdev_issue_write_zeroes(struct block_device *bdev,
                 sector_t sector, sector_t nr_sects, gfp_t gfp_mask,
                 struct bio **biop, unsigned flags)
@@ -216,6 +243,7 @@ static int __blkdev_issue_write_zeroes(struct
block_device *bdev,
         struct bio *bio = *biop;
         unsigned int max_write_zeroes_sectors;
         struct request_queue *q = bdev_get_queue(bdev);
+       unsigned int unmap = (flags & BLKDEV_ZERO_NOUNMAP) ? REQ_NOUNMAP
: 0;

         if (!q)
                 return -ENXIO;
@@ -229,24 +257,8 @@ static int __blkdev_issue_write_zeroes(struct
block_device *bdev,
         if (max_write_zeroes_sectors == 0)
                 return -EOPNOTSUPP;

-       while (nr_sects) {
-               bio = blk_next_bio(bio, 0, gfp_mask);
-               bio->bi_iter.bi_sector = sector;
-               bio_set_dev(bio, bdev);
-               bio->bi_opf = REQ_OP_WRITE_ZEROES;
-               if (flags & BLKDEV_ZERO_NOUNMAP)
-                       bio->bi_opf |= REQ_NOUNMAP;
-
-               if (nr_sects > max_write_zeroes_sectors) {
-                       bio->bi_iter.bi_size = max_write_zeroes_sectors
<< 9;
-                       nr_sects -= max_write_zeroes_sectors;
-                       sector += max_write_zeroes_sectors;
-               } else {
-                       bio->bi_iter.bi_size = nr_sects << 9;
-                       nr_sects = 0;
-               }
-               cond_resched();
-       }
+       __blkdev_issue_payloadless(bdev, REQ_OP_WRITE_ZEROES, sector,
nr_sects,
+                       gfp_mask, biop, unmap, max_write_zeroes_sectors);

         *biop = bio;
         return 0;

I'll be happy to send out a well tested patch based on the above
suggestion or any feedback I get and re-spin this series or OP can
re-spin this series whatever works.

      reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13  7:39 Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 1/6] block: Add @flags argument to bdev_write_zeroes_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 2/6] block: Pass op_flags into blk_queue_get_max_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 3/6] block: Introduce blk_queue_get_max_write_zeroes_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 4/6] block: Add support for REQ_ALLOCATE flag Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 5/6] block: Add blk_queue_max_allocate_sectors() Kirill Tkhai
2020-02-13  7:39 ` [PATCH v7 6/6] loop: Add support for REQ_ALLOCATE Kirill Tkhai
2020-02-13 18:11   ` Darrick J. Wong
2020-02-13 20:07     ` Kirill Tkhai
2020-02-13  7:55 ` [PATCH v7 0/6] block: Introduce REQ_ALLOCATE flag for REQ_OP_WRITE_ZEROES Kirill Tkhai
2020-03-06  9:11   ` Kirill Tkhai
2020-03-13 13:08     ` Kirill Tkhai
2020-03-19 10:28       ` Christoph Hellwig
2020-03-19 10:42         ` Kirill Tkhai
2020-03-19 13:03         ` Martin K. Petersen
2020-03-25 16:26           ` Darrick J. Wong
2020-03-25 16:32             ` Christoph Hellwig
2020-03-25 17:23               ` Martin K. Petersen
2020-03-26  9:29                 ` Christoph Hellwig
2020-03-26 14:34                   ` Martin K. Petersen
2020-03-26 14:45                     ` Christoph Hellwig
2020-03-26 16:48                       ` Chaitanya Kulkarni [this message]

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