Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947475AbbGaVUO (ORCPT ); Fri, 31 Jul 2015 17:20:14 -0400 Received: from mail.kernel.org ([198.145.29.136]:56463 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752469AbbGaVUJ (ORCPT ); Fri, 31 Jul 2015 17:20:09 -0400 MIME-Version: 1.0 In-Reply-To: <20150731192337.GA8907@redhat.com> References: <1436168690-32102-1-git-send-email-mlin@kernel.org> <20150731192337.GA8907@redhat.com> Date: Fri, 31 Jul 2015 14:19:55 -0700 Message-ID: Subject: Re: [PATCH v5 01/11] block: make generic_make_request handle arbitrarily sized bios From: Ming Lin To: Mike Snitzer Cc: lkml , Christoph Hellwig , Jens Axboe , Kent Overstreet , Dongsu Park , Christoph Hellwig , Al Viro , Ming Lei , Neil Brown , Alasdair Kergon , dm-devel@redhat.com, Lars Ellenberg , drbd-user@lists.linbit.com, Jiri Kosina , Geoff Levand , Jim Paris , Joshua Morris , Philip Kelleher , Minchan Kim , Nitin Gupta , Oleg Drokin , Andreas Dilger , Ming Lin Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7363 Lines: 158 On Fri, Jul 31, 2015 at 12:23 PM, Mike Snitzer wrote: > On Mon, Jul 06 2015 at 3:44P -0400, > Ming Lin wrote: > >> From: Kent Overstreet >> >> 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 >> Cc: Christoph Hellwig >> Cc: Al Viro >> Cc: Ming Lei >> Cc: Neil Brown >> Cc: Alasdair Kergon >> Cc: Mike Snitzer >> Cc: dm-devel@redhat.com >> Cc: Lars Ellenberg >> Cc: drbd-user@lists.linbit.com >> Cc: Jiri Kosina >> Cc: Geoff Levand >> Cc: Jim Paris >> Cc: Joshua Morris >> Cc: Philip Kelleher >> Cc: Minchan Kim >> Cc: Nitin Gupta >> Cc: Oleg Drokin >> Cc: Andreas Dilger >> Acked-by: NeilBrown (for the 'md/md.c' bits) >> Signed-off-by: Kent Overstreet >> [dpark: skip more mq-based drivers, resolve merge conflicts, etc.] >> Signed-off-by: Dongsu Park >> Signed-off-by: Ming Lin > ... >> 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. Ming > > 4) Failure: > test_discard_a_fragmented_device(DiscardQuickTests) > [/root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:49:in `block in assert_no_mappings' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:43:in `call' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:43:in `block in with_dev_md' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:40:in `each' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:40:in `with_dev_md' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:48:in `assert_no_mappings' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:263:in `test_discard_a_fragmented_device']: > <0> expected but was > <131072>. > > 5) Failure: > test_discard_fully_provisioned_device_benchmark(DiscardQuickTests) > [/root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:49:in `block in assert_no_mappings' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:43:in `call' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:43:in `block in with_dev_md' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:40:in `each' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:40:in `with_dev_md' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:48:in `assert_no_mappings' > /root/snitm/git/device-mapper-test-suite/lib/dmtest/tests/thin-provisioning/discard_tests.rb:225:in `test_discard_fully_provisioned_device_benchmark']: > <0> expected but was > <262144>. > > But I haven't yet figured out where the blk_bio_discard_split code, or > elsewhere, is going wrong. > > Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/