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[68.160.166.30]) by smtp.gmail.com with ESMTPSA id m14-20020a05620a13ae00b0075da00ef114sm693183qki.46.2023.06.08.17.28.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Jun 2023 17:28:17 -0700 (PDT) Date: Thu, 8 Jun 2023 20:28:16 -0400 From: Mike Snitzer To: Sarthak Kukreti , Joe Thornber , Brian Foster Cc: dm-devel@redhat.com, linux-block@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jens Axboe , Theodore Ts'o , "Michael S. Tsirkin" , "Darrick J. Wong" , Jason Wang , Bart Van Assche , Christoph Hellwig , Andreas Dilger , Stefan Hajnoczi , Alasdair Kergon Subject: Re: [PATCH v7 4/5] dm-thin: Add REQ_OP_PROVISION support Message-ID: References: <20230518223326.18744-1-sarthakkukreti@chromium.org> <20230518223326.18744-5-sarthakkukreti@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 08 2023 at 5:24P -0400, Mike Snitzer wrote: > On Fri, May 19 2023 at 11:23P -0400, > Mike Snitzer wrote: > > > On Thu, May 18 2023 at 6:33P -0400, > > Sarthak Kukreti wrote: > > > > > dm-thinpool uses the provision request to provision > > > blocks for a dm-thin device. dm-thinpool currently does not > > > pass through REQ_OP_PROVISION to underlying devices. > > > > > > For shared blocks, provision requests will break sharing and copy the > > > contents of the entire block. Additionally, if 'skip_block_zeroing' > > > is not set, dm-thin will opt to zero out the entire range as a part > > > of provisioning. > > > > > > Signed-off-by: Sarthak Kukreti > > > --- > > > drivers/md/dm-thin.c | 74 +++++++++++++++++++++++++++++++++++++++++--- > > > 1 file changed, 70 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c > > > index 2b13c949bd72..f1b68b558cf0 100644 > > > --- a/drivers/md/dm-thin.c > > > +++ b/drivers/md/dm-thin.c > > > @@ -1245,8 +1247,8 @@ static int io_overlaps_block(struct pool *pool, struct bio *bio) > > > > > > static int io_overwrites_block(struct pool *pool, struct bio *bio) > > > { > > > - return (bio_data_dir(bio) == WRITE) && > > > - io_overlaps_block(pool, bio); > > > + return (bio_data_dir(bio) == WRITE) && io_overlaps_block(pool, bio) && > > > + bio_op(bio) != REQ_OP_PROVISION; > > > } > > > > > > static void save_and_set_endio(struct bio *bio, bio_end_io_t **save, > > > @@ -1394,6 +1396,9 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block, > > > m->data_block = data_block; > > > m->cell = cell; > > > > > > + if (bio && bio_op(bio) == REQ_OP_PROVISION) > > > + m->bio = bio; > > > + > > > /* > > > * If the whole block of data is being overwritten or we are not > > > * zeroing pre-existing data, we can issue the bio immediately. > > > > This doesn't seem like the best way to address avoiding passdown of > > provision bios (relying on process_prepared_mapping's implementation > > that happens to do the right thing if m->bio set). Doing so cascades > > into relying on complete_overwrite_bio() happening to _not_ actually > > being specific to "overwrite" bios. > > > > I don't have a better suggestion yet but will look closer. Just think > > this needs to be formalized a bit more rather than it happening to > > "just work". > > > > Cc'ing Joe to see what he thinks too. This is something we can clean > > up with a follow-on patch though, so not a show-stopper for this > > series. > > I haven't circled back to look close enough at this but > REQ_OP_PROVISION bios _are_ being passed down to the thin-pool's > underlying data device. > > Brian Foster reported that if he issues a REQ_OP_PROVISION to a thin > device after a snapshot (to break sharing), it'll fail with > -EOPNOTSUPP (response is from bio being passed down to device that > doesn't support it). I was able to reproduce with: > > # fallocate --offset 0 --length 1048576 /dev/test/thin > # lvcreate -n snap --snapshot test/thin > > # fallocate --offset 0 --length 1048576 /dev/test/thin > fallocate: fallocate failed: Operation not supported > > But reports success when retried: > # fallocate --offset 0 --length 1048576 /dev/test/thin > # echo $? > 0 > > It's somewhat moot in that Joe will be reimplementing handling for > REQ_OP_PROVISION _but_ in the meantime it'd be nice to have a version > of this patch that doesn't error (due to passdown of REQ_OP_PROVISION) > when breaking sharing. Primarily so the XFS guys (Dave and Brian) can > make progress. > > I'll take a closer look tomorrow but figured I'd let you know. This fixes the issue for me (causes process_prepared_mapping to end the bio without REQ_OP_PROVISION passdown). But like I said above back on May 19: needs cleanup to make it less of a hack for the REQ_OP_PROVISION case. At a minimum complete_overwrite_bio() would need renaming. diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index 43a6702f9efe..434a3b37af2f 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -1324,6 +1324,9 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block, m->data_block = data_dest; m->cell = cell; + if (bio_op(bio) == REQ_OP_PROVISION) + m->bio = bio; + /* * quiesce action + copy action + an extra reference held for the * duration of this function (we may need to inc later for a