From: Nikolay Borisov <nborisov@suse.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Omar Sandoval <osandov@osandov.com>,
linux-block@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Possible bio merging breakage in mp bio rework
Date: Fri, 5 Apr 2019 19:04:18 +0300 [thread overview]
Message-ID: <59c19acf-999f-1911-b0b8-1a5cec8116c5@suse.com> (raw)
Hello Ming,
Following the mp biovec rework what is the maximum
data that a bio could contain? Should it be PAGE_SIZE * bio_vec
or something else? Currently I can see bios as large as 127 megs
on sequential workloads, I got prompted to this since btrfs has a
memory allocation that is dependent on the data in the bio and this
particular memory allocation started failing with order 6 allocs.
Further debugging showed that with the following xfs_io command line:
xfs_io -f -c "pwrite -S 0x61 -b 4m 0 10g" /media/scratch/file1
I can easily see very large bios:
[ 188.366540] kworker/-7 3.... 34847519us : btrfs_submit_bio_hook: bio: ffff8dffe9940bb0 bi_iter.bi_size = 134184960 bi_vcn: 28 bi_vcnt_max: 256
[ 188.367129] kworker/-658 2.... 34946536us : btrfs_submit_bio_hook: bio: ffff8dffe9940370 bi_iter.bi_size = 134246400 bi_vcn: 28 bi_vcnt_max: 256
[ 188.367714] kworker/-7 3.... 35107967us : btrfs_submit_bio_hook: bio: ffff8dffe9940bb0 bi_iter.bi_size = 134184960 bi_vcn: 30 bi_vcnt_max: 256
[ 188.368319] kworker/-658 2.... 35229894us : btrfs_submit_bio_hook: bio: ffff8dffe9940370 bi_iter.bi_size = 134246400 bi_vcn: 32 bi_vcnt_max: 256
[ 188.368909] kworker/-7 3.... 35374809us : btrfs_submit_bio_hook: bio: ffff8dffe9940bb0 bi_iter.bi_size = 134184960 bi_vcn: 25 bi_vcnt_max: 256
[ 188.369498] kworker/-658 2.... 35516194us : btrfs_submit_bio_hook: bio: ffff8dffe9940370 bi_iter.bi_size = 134246400 bi_vcn: 31 bi_vcnt_max: 256
[ 188.370086] kworker/-7 3.... 35663669us : btrfs_submit_bio_hook: bio: ffff8dffe9940bb0 bi_iter.bi_size = 134184960 bi_vcn: 32 bi_vcnt_max: 256
[ 188.370696] kworker/-658 2.... 35791006us : btrfs_submit_bio_hook: bio: ffff8dffe9940370 bi_iter.bi_size = 100655104 bi_vcn: 24 bi_vcnt_max: 256
[ 188.371335] kworker/-658 2.... 35816114us : btrfs_submit_bio_hook: bio: ffff8dffe99434f0 bi_iter.bi_size = 33591296 bi_vcn: 5 bi_vcnt_max: 256
So that's 127 megs in a single bio? This stems from the new merging logic.
07173c3ec276 ("block: enable multipage bvecs") made it so that physically
contiguous pages added to the bio would just modify bi_iter.bi_size and the
initial page's bio_vec's bv_len. There's no longer the
page == bv->bv_page portion of the check.
next reply other threads:[~2019-04-05 16:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-05 16:04 Nikolay Borisov [this message]
2019-04-06 0:16 ` Possible bio merging breakage in mp bio rework Ming Lei
2019-04-06 6:09 ` Nikolay Borisov
2019-04-06 8:00 ` Qu Wenruo
2019-04-06 12:30 ` Ming Lei
2019-04-08 9:52 ` Johannes Thumshirn
2019-04-08 10:19 ` Ming Lei
2019-04-08 10:22 ` Johannes Thumshirn
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