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[68.160.166.30]) by smtp.gmail.com with ESMTPSA id g16-20020ac84690000000b003f8e6071e43sm669752qto.3.2023.06.08.14.24.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Jun 2023 14:24:48 -0700 (PDT) Date: Thu, 8 Jun 2023 17:24:47 -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 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. Mike