Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Fri, 2015-07-31 at 17:38 -0400, Mike Snitzer wrote:
> On Fri, Jul 31 2015 at 5:19pm -0400,
> Ming Lin <mlin at kernel.org> wrote:
>
> > On Fri, Jul 31, 2015 at 12:23 PM, Mike Snitzer <snitzer at redhat.com> wrote:
> > > On Mon, Jul 06 2015 at 3:44P -0400,
> > > Ming Lin <mlin at kernel.org> wrote:
> > >
> > >> From: Kent Overstreet <kent.overstreet at gmail.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 at kernel.dk>
> > >> Cc: Christoph Hellwig <hch at infradead.org>
> > >> Cc: Al Viro <viro at zeniv.linux.org.uk>
> > >> Cc: Ming Lei <ming.lei at canonical.com>
> > >> Cc: Neil Brown <neilb at suse.de>
> > >> Cc: Alasdair Kergon <agk at redhat.com>
> > >> Cc: Mike Snitzer <snitzer at redhat.com>
> > >> Cc: dm-devel at redhat.com
> > >> Cc: Lars Ellenberg <drbd-dev at lists.linbit.com>
> > >> Cc: drbd-user at lists.linbit.com
> > >> Cc: Jiri Kosina <jkosina at suse.cz>
> > >> Cc: Geoff Levand <geoff at infradead.org>
> > >> Cc: Jim Paris <jim at jtan.com>
> > >> Cc: Joshua Morris <josh.h.morris at us.ibm.com>
> > >> Cc: Philip Kelleher <pjk1939 at linux.vnet.ibm.com>
> > >> Cc: Minchan Kim <minchan at kernel.org>
> > >> Cc: Nitin Gupta <ngupta at vflare.org>
> > >> Cc: Oleg Drokin <oleg.drokin at intel.com>
> > >> Cc: Andreas Dilger <andreas.dilger at intel.com>
> > >> Acked-by: NeilBrown <neilb at suse.de> (for the 'md/md.c' bits)
> > >> Signed-off-by: Kent Overstreet <kent.overstreet at gmail.com>
> > >> [dpark: skip more mq-based drivers, resolve merge conflicts, etc.]
> > >> Signed-off-by: Dongsu Park <dpark at posteo.net>
> > >> Signed-off-by: Ming Lin <ming.l at ssi.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.
It's caused by patch 4.
When discard size >=4G, the bio->bi_iter.bi_size overflows.
Below is the new patch.
Christoph,
Could you also help to review it?
Now we still do "misaligned" check in blkdev_issue_discard().
So the same code in blk_bio_discard_split() was removed.
Please see
https://git.kernel.org/cgit/linux/kernel/git/mlin/linux.git/commit/?h=block-generic-req&id=dcc5d9c41
I have updated both patch 1 & 4 on my tree.
commit 9607f737de9c4ca1a81655c320a61c287bf77bf5
Author: Ming Lin <ming.l at ssi.samsung.com>
Date: Fri May 22 00:46:56 2015 -0700
block: remove split code in blkdev_issue_discard
The split code in blkdev_issue_discard() can go away now
that any driver that cares does the split, all we have
to do is make sure bio size doesn't overflow.
Signed-off-by: Ming Lin <ming.l at ssi.samsung.com>
---
block/blk-lib.c | 16 +++-------------
1 file changed, 3 insertions(+), 13 deletions(-)
diff --git a/block/blk-lib.c b/block/blk-lib.c
index 7688ee3..b9e2fca 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -43,7 +43,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
DECLARE_COMPLETION_ONSTACK(wait);
struct request_queue *q = bdev_get_queue(bdev);
int type = REQ_WRITE | REQ_DISCARD;
- unsigned int max_discard_sectors, granularity;
+ unsigned int granularity;
int alignment;
struct bio_batch bb;
struct bio *bio;
@@ -60,17 +60,6 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
granularity = max(q->limits.discard_granularity >> 9, 1U);
alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;
- /*
- * Ensure that max_discard_sectors is of the proper
- * granularity, so that requests stay aligned after a split.
- */
- max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
- max_discard_sectors -= max_discard_sectors % granularity;
- if (unlikely(!max_discard_sectors)) {
- /* Avoid infinite loop below. Being cautious never hurts. */
- return -EOPNOTSUPP;
- }
-
if (flags & BLKDEV_DISCARD_SECURE) {
if (!blk_queue_secdiscard(q))
return -EOPNOTSUPP;
@@ -92,7 +81,8 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
break;
}
- req_sects = min_t(sector_t, nr_sects, max_discard_sectors);
+ /* Make sure bi_size doesn't overflow */
+ req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
/*
* If splitting a request, and the next starting sector would be