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Message-ID: <CAF1ivSa4vX2g5eqMfVAgdeoMGbJ7wQ8GfLmSbU=L96pSQirC5w@mail.gmail.com>
Date: Fri, 31 Jul 2015 15:18:52 -0700
From: Ming Lin <mlin@...nel.org>
To: Mike Snitzer <snitzer@...hat.com>
Cc: lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 01/11] block: make generic_make_request handle
arbitrarily sized bios
On Fri, Jul 31, 2015 at 3:02 PM, Ming Lin <mlin@...nel.org> wrote:
> On Fri, 2015-07-31 at 17:38 -0400, Mike Snitzer wrote:
>> On Fri, Jul 31 2015 at 5:19pm -0400,
>> Ming Lin <mlin@...nel.org> wrote:
>>
>> > On Fri, Jul 31, 2015 at 12:23 PM, Mike Snitzer <snitzer@...hat.com> wrote:
>> > > On Mon, Jul 06 2015 at 3:44P -0400,
>> > > Ming Lin <mlin@...nel.org> wrote:
>> > >
>> > >> From: Kent Overstreet <kent.overstreet@...il.com>
>> > >>
>> > >> The way the block layer is currently written, it goes to great lengths
>> > >> to avoid having to split bios; upper layer code (such as bio_add_page())
>> > >> checks what the underlying device can handle and tries to always create
>> > >> bios that don't need to be split.
>> > >>
>> > >> But this approach becomes unwieldy and eventually breaks down with
>> > >> stacked devices and devices with dynamic limits, and it adds a lot of
>> > >> complexity. If the block layer could split bios as needed, we could
>> > >> eliminate a lot of complexity elsewhere - particularly in stacked
>> > >> drivers. Code that creates bios can then create whatever size bios are
>> > >> convenient, and more importantly stacked drivers don't have to deal with
>> > >> both their own bio size limitations and the limitations of the
>> > >> (potentially multiple) devices underneath them. In the future this will
>> > >> let us delete merge_bvec_fn and a bunch of other code.
>> > >>
>> > >> We do this by adding calls to blk_queue_split() to the various
>> > >> make_request functions that need it - a few can already handle arbitrary
>> > >> size bios. Note that we add the call _after_ any call to
>> > >> blk_queue_bounce(); this means that blk_queue_split() and
>> > >> blk_recalc_rq_segments() don't need to be concerned with bouncing
>> > >> affecting segment merging.
>> > >>
>> > >> Some make_request_fn() callbacks were simple enough to audit and verify
>> > >> they don't need blk_queue_split() calls. The skipped ones are:
>> > >>
>> > >> * nfhd_make_request (arch/m68k/emu/nfblock.c)
>> > >> * axon_ram_make_request (arch/powerpc/sysdev/axonram.c)
>> > >> * simdisk_make_request (arch/xtensa/platforms/iss/simdisk.c)
>> > >> * brd_make_request (ramdisk - drivers/block/brd.c)
>> > >> * mtip_submit_request (drivers/block/mtip32xx/mtip32xx.c)
>> > >> * loop_make_request
>> > >> * null_queue_bio
>> > >> * bcache's make_request fns
>> > >>
>> > >> Some others are almost certainly safe to remove now, but will be left
>> > >> for future patches.
>> > >>
>> > >> Cc: Jens Axboe <axboe@...nel.dk>
>> > >> Cc: Christoph Hellwig <hch@...radead.org>
>> > >> Cc: Al Viro <viro@...iv.linux.org.uk>
>> > >> Cc: Ming Lei <ming.lei@...onical.com>
>> > >> Cc: Neil Brown <neilb@...e.de>
>> > >> Cc: Alasdair Kergon <agk@...hat.com>
>> > >> Cc: Mike Snitzer <snitzer@...hat.com>
>> > >> Cc: dm-devel@...hat.com
>> > >> Cc: Lars Ellenberg <drbd-dev@...ts.linbit.com>
>> > >> Cc: drbd-user@...ts.linbit.com
>> > >> Cc: Jiri Kosina <jkosina@...e.cz>
>> > >> Cc: Geoff Levand <geoff@...radead.org>
>> > >> Cc: Jim Paris <jim@...n.com>
>> > >> Cc: Joshua Morris <josh.h.morris@...ibm.com>
>> > >> Cc: Philip Kelleher <pjk1939@...ux.vnet.ibm.com>
>> > >> Cc: Minchan Kim <minchan@...nel.org>
>> > >> Cc: Nitin Gupta <ngupta@...are.org>
>> > >> Cc: Oleg Drokin <oleg.drokin@...el.com>
>> > >> Cc: Andreas Dilger <andreas.dilger@...el.com>
>> > >> Acked-by: NeilBrown <neilb@...e.de> (for the 'md/md.c' bits)
>> > >> Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>
>> > >> [dpark: skip more mq-based drivers, resolve merge conflicts, etc.]
>> > >> Signed-off-by: Dongsu Park <dpark@...teo.net>
>> > >> Signed-off-by: Ming Lin <ming.l@....samsung.com>
>> > > ...
>> > >> diff --git a/block/blk-merge.c b/block/blk-merge.c
>> > >> index 30a0d9f..3707f30 100644
>> > >> --- a/block/blk-merge.c
>> > >> +++ b/block/blk-merge.c
>> > >> @@ -9,12 +9,158 @@
>> > >>
>> > >> #include "blk.h"
>> > >>
>> > >> +static struct bio *blk_bio_discard_split(struct request_queue *q,
>> > >> + struct bio *bio,
>> > >> + struct bio_set *bs)
>> > >> +{
>> > >> + unsigned int max_discard_sectors, granularity;
>> > >> + int alignment;
>> > >> + sector_t tmp;
>> > >> + unsigned split_sectors;
>> > >> +
>> > >> + /* Zero-sector (unknown) and one-sector granularities are the same. */
>> > >> + granularity = max(q->limits.discard_granularity >> 9, 1U);
>> > >> +
>> > >> + max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
>> > >> + max_discard_sectors -= max_discard_sectors % granularity;
>> > >> +
>> > >> + if (unlikely(!max_discard_sectors)) {
>> > >> + /* XXX: warn */
>> > >> + return NULL;
>> > >> + }
>> > >> +
>> > >> + if (bio_sectors(bio) <= max_discard_sectors)
>> > >> + return NULL;
>> > >> +
>> > >> + split_sectors = max_discard_sectors;
>> > >> +
>> > >> + /*
>> > >> + * If the next starting sector would be misaligned, stop the discard at
>> > >> + * the previous aligned sector.
>> > >> + */
>> > >> + alignment = (q->limits.discard_alignment >> 9) % granularity;
>> > >> +
>> > >> + tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
>> > >> + tmp = sector_div(tmp, granularity);
>> > >> +
>> > >> + if (split_sectors > tmp)
>> > >> + split_sectors -= tmp;
>> > >> +
>> > >> + return bio_split(bio, split_sectors, GFP_NOIO, bs);
>> > >> +}
>> > >
>> > > This code to stop the discard at the previous aligned sector could be
>> > > the reason why I have 2 device-mapper-test-suite tests in the
>> > > 'thin-provisioning' testsuite failing due to this patchset:
>> >
>> > I'm setting up the testsuite to debug.
>>
>> OK, once setup, to run the 2 tests in question directly you'd do
>> something like:
>>
>> dmtest run --suite thin-provisioning -n discard_a_fragmented_device
>>
>> dmtest run --suite thin-provisioning -n discard_fully_provisioned_device_benchmark
>>
>> Again, these tests pass without this patchset.
>
> (trim CC list)
>
> I followed
> https://github.com/jthornber/device-mapper-test-suite
> https://github.com/jthornber/thin-provisioning-tools
>
> to setup.
>
> $ grep CONFIG_DM_ .config
> CONFIG_DM_MQ_DEFAULT=y
> CONFIG_DM_DEBUG=y
> CONFIG_DM_BUFIO=y
> CONFIG_DM_BIO_PRISON=y
> CONFIG_DM_PERSISTENT_DATA=y
> # CONFIG_DM_DEBUG_BLOCK_STACK_TRACING is not set
> CONFIG_DM_CRYPT=y
> CONFIG_DM_SNAPSHOT=y
> CONFIG_DM_THIN_PROVISIONING=y
> CONFIG_DM_CACHE=y
> CONFIG_DM_CACHE_MQ=y
> CONFIG_DM_CACHE_SMQ=y
> CONFIG_DM_CACHE_CLEANER=y
> CONFIG_DM_ERA=y
> CONFIG_DM_MIRROR=y
> CONFIG_DM_LOG_USERSPACE=y
> CONFIG_DM_RAID=y
> CONFIG_DM_ZERO=y
> CONFIG_DM_MULTIPATH=y
> CONFIG_DM_MULTIPATH_QL=y
> CONFIG_DM_MULTIPATH_ST=y
> CONFIG_DM_DELAY=y
> CONFIG_DM_UEVENT=y
> CONFIG_DM_FLAKEY=y
> CONFIG_DM_VERITY=y
> CONFIG_DM_SWITCH=y
> CONFIG_DM_LOG_WRITES=y
>
>
> # cat .dmtest/config
> profile :ssd do
> metadata_dev '/dev/vda'
> data_dev '/dev/vdb'
> end
OK, virtio-blk doesn't support discard.
I could reproduce it with virtio-scsi.
Now debugging ...
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