[PATCHSET 1/3 v3 block/for-4.1/core] writeback: cgroup writeback support

Tejun Heo
2015-04-06T19:58:55Z

Subject: [PATCHSET 1/3 v3 block/for-4.1/core] writeback: cgroup writeback support

Hello,

This is v3 of cgroup writeback support patchset. Changes from the
last take[L] are

* mapping_congested() is now inode_congested() and always operates on
the inode regardless of the current task. This was broken in the
last take due to the logic carried over from multi-wb dirtying in
the first take. Noticed by Vivek.

* Fengguang noticed crash from the split congestion code when there's
no blkcg policy active. This is caused by blkcg pointlessly trying
to micro optimize the allocation of root blkcg_gq and has caused
similar bugs before.
0004-blkcg-always-create-the-blkcg_gq-for-the-root-blkcg.patch
added.

* Some minor bug fixes and cosmetic updates. Nothing too interesting.

blkio cgroup (blkcg) is severely crippled in that it can only control
read and direct write IOs. blkcg can't tell which cgroup should be
held responsible for a given writeback IO and charges all of them to
the root cgroup - all normal write traffic ends up in the root cgroup.
Although the problem has been identified years ago, mainly because it
interacts with so many subsystems, it hasn't been solved yet.

This patchset finally implements cgroup writeback support so that
writeback of a page is attributed to the corresponding blkcg of the
memcg that the page belongs to.

Overall design
--------------

* This requires cooperation between memcg and blkcg. Each inode is
assigned to the blkcg mapped to the memcg being dirtied.

* struct bdi_writeback (wb) was always embedded in struct
backing_dev_info (bdi) and the distinction between the two wasn't
clear. This patchset makes wb operate as an independent writeback
execution domain. bdi->wb is still embedded and serves the root
cgroup but there can be other wb's for other cgroups.

* Each wb is associated with memcg. As memcg is implicitly enabled by
blkcg on the unified hierarchy, this gives a unique wb for each
memcg-blkcg combination. When memcg-blkcg mapping changes, a new wb
is created and the existing wb is unlinked and drained.

* An inode is associated with the matching wb when it gets dirtied for
the first time and written back by that wb. A later patchset will
implement dynamic wb switching.

* All writeback operations are made per-wb instead of per-bdi.
bdi-wide operations are split across all member wb's. If some
finite amount needs to be distributed, be it number of pages to
writeback or bdi->min/max_ratio, it's distributed according to the
bandwidth proportion a wb has in the bdi.

* cgroup writeback support adds one pointer to struct inode.

Missing pieces
--------------

* It requires some cooperation from the filesystem and currently only
works with ext2. The changes necessary on the filesystem side are
almost trivial. I'll write up a documentation on it.

* blk-throttle works but cfq-iosched isn't ready for writebacks coming
down with different cgroups. cfq-iosched should be updated to have
a writeback ioc per cgroup and route writeback IOs through it.

How to test
-----------

* Boot with kernel option "cgroup__DEVEL__legacy_files_on_dfl".

* umount /sys/fs/cgroup/memory
umount /sys/fs/cgroup/blkio
mkdir /sys/fs/cgroup/unified
mount -t cgroup -o __DEVEL__sane_behavior cgroup /sys/fs/cgroup/unified
echo +blkio > /sys/fs/cgroup/unified/cgroup.subtree_control

* Build the cgroup hierarchy (don't forget to enable blkio using
subtree_control) and put processes in cgroups and run tests on ext2
filesystems and blkio.throttle.* knobs.

This patchset contains the following 48 patches.

0001-memcg-add-per-cgroup-dirty-page-accounting.patch
0002-blkcg-move-block-blk-cgroup.h-to-include-linux-blk-c.patch
0003-update-CONFIG_BLK_CGROUP-dummies-in-include-linux-bl.patch
0004-blkcg-always-create-the-blkcg_gq-for-the-root-blkcg.patch
0005-memcg-add-mem_cgroup_root_css.patch
0006-blkcg-add-blkcg_root_css.patch
0007-cgroup-block-implement-task_get_css-and-use-it-in-bi.patch
0008-blkcg-implement-task_get_blkcg_css.patch
0009-blkcg-implement-bio_associate_blkcg.patch
0010-memcg-implement-mem_cgroup_css_from_page.patch
0011-writeback-move-backing_dev_info-state-into-bdi_write.patch
0012-writeback-move-backing_dev_info-bdi_stat-into-bdi_wr.patch
0013-writeback-move-bandwidth-related-fields-from-backing.patch
0014-writeback-s-bdi-wb-in-mm-page-writeback.c.patch
0015-writeback-move-backing_dev_info-wb_lock-and-worklist.patch
0016-writeback-reorganize-mm-backing-dev.c.patch
0017-writeback-separate-out-include-linux-backing-dev-def.patch
0018-bdi-make-inode_to_bdi-inline.patch
0019-writeback-add-gfp-to-wb_init.patch
0020-bdi-separate-out-congested-state-into-a-separate-str.patch
0021-writeback-add-CONFIG-BDI_CAP-FS-_CGROUP_WRITEBACK.patch
0022-writeback-make-backing_dev_info-host-cgroup-specific.patch
0023-writeback-blkcg-associate-each-blkcg_gq-with-the-cor.patch
0024-writeback-attribute-stats-to-the-matching-per-cgroup.patch
0025-writeback-let-balance_dirty_pages-work-on-the-matchi.patch
0026-writeback-make-congestion-functions-per-bdi_writebac.patch
0027-writeback-blkcg-restructure-blk_-set-clear-_queue_co.patch
0028-writeback-blkcg-propagate-non-root-blkcg-congestion-.patch
0029-writeback-implement-and-use-inode_congested.patch
0030-writeback-implement-WB_has_dirty_io-wb_state-flag.patch
0031-writeback-implement-backing_dev_info-tot_write_bandw.patch
0032-writeback-make-bdi_has_dirty_io-take-multiple-bdi_wr.patch
0033-writeback-don-t-issue-wb_writeback_work-if-clean.patch
0034-writeback-make-bdi-min-max_ratio-handling-cgroup-wri.patch
0035-writeback-implement-bdi_for_each_wb.patch
0036-writeback-remove-bdi_start_writeback.patch
0037-writeback-make-laptop_mode_timer_fn-handle-multiple-.patch
0038-writeback-make-writeback_in_progress-take-bdi_writeb.patch
0039-writeback-make-bdi_start_background_writeback-take-b.patch
0040-writeback-make-wakeup_flusher_threads-handle-multipl.patch
0041-writeback-add-wb_writeback_work-auto_free.patch
0042-writeback-implement-bdi_wait_for_completion.patch
0043-writeback-implement-wb_wait_for_single_work.patch
0044-writeback-restructure-try_writeback_inodes_sb-_nr.patch
0045-writeback-make-writeback-initiation-functions-handle.patch
0046-writeback-dirty-inodes-against-their-matching-cgroup.patch
0047-buffer-writeback-make-__block_write_full_page-honor-.patch
0048-mpage-make-__mpage_writepage-honor-cgroup-writeback.patch
0049-ext2-enable-cgroup-writeback-support.patch

0001-0020 are preps.

0021-0046 gradually convert writeback code so that wb (bdi_writeback)
operates as an independent writeback domain instead of bdi
(backing_dev_info), a single bdi can have multiple per-cgroup wb's
working for it, and per-bdi operations are translated and distributed
to all its member wb's.

0047-0049 make lower layers to properly propagate the cgroup
association from the writeback layer and enable cgroup writeback on
ext2.

This patchset is on top of

block/for-4.1/core bfd343aa1718 ("blk-mq: don't wait in blk_mq_queue_enter() if __GFP_WAIT isn't set")
+ [1] [PATCH] writeback: fix possible underflow in write bandwidth calculation

and available in the following git branch.

git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-cgroup-writeback-20150406

diffstat follows. Thanks.

Documentation/cgroups/memory.txt | 1
block/bio.c | 35 +-
block/blk-cgroup.c | 124 +++----
block/blk-cgroup.h | 603 -----------------------------------
block/blk-core.c | 70 ++--
block/blk-integrity.c | 1
block/blk-sysfs.c | 3
block/blk-throttle.c | 2
block/bounce.c | 1
block/cfq-iosched.c | 2
block/elevator.c | 2
block/genhd.c | 1
drivers/block/drbd/drbd_int.h | 1
drivers/block/drbd/drbd_main.c | 10
drivers/block/pktcdvd.c | 1
drivers/char/raw.c | 1
drivers/md/bcache/request.c | 1
drivers/md/dm.c | 2
drivers/md/dm.h | 1
drivers/md/md.h | 1
drivers/md/raid1.c | 4
drivers/md/raid10.c | 2
drivers/mtd/devices/block2mtd.c | 1
fs/block_dev.c | 9
fs/buffer.c | 60 ++-
fs/ext2/super.c | 2
fs/ext4/extents.c | 1
fs/ext4/mballoc.c | 1
fs/ext4/super.c | 1
fs/f2fs/node.c | 4
fs/f2fs/segment.h | 3
fs/fs-writeback.c | 599 +++++++++++++++++++++++++----------
fs/fuse/file.c | 12
fs/gfs2/super.c | 2
fs/hfs/super.c | 1
fs/hfsplus/super.c | 1
fs/inode.c | 1
fs/mpage.c | 2
fs/nfs/filelayout/filelayout.c | 1
fs/nfs/internal.h | 2
fs/nfs/write.c | 3
fs/ocfs2/file.c | 1
fs/reiserfs/super.c | 1
fs/ufs/super.c | 1
fs/xfs/xfs_aops.c | 12
fs/xfs/xfs_file.c | 1
include/linux/backing-dev-defs.h | 188 +++++++++++
include/linux/backing-dev.h | 567 ++++++++++++++++++++++++---------
include/linux/bio.h | 3
include/linux/blk-cgroup.h | 631 ++++++++++++++++++++++++++++++++++++
include/linux/blkdev.h | 21 -
include/linux/cgroup.h | 25 +
include/linux/fs.h | 13
include/linux/memcontrol.h | 10
include/linux/mm.h | 3
include/linux/pagemap.h | 3
include/linux/writeback.h | 25 -
include/trace/events/writeback.h | 8
init/Kconfig | 5
mm/backing-dev.c | 666 +++++++++++++++++++++++++++++++--------
mm/fadvise.c | 2
mm/filemap.c | 32 +
mm/madvise.c | 1
mm/memcontrol.c | 59 +++
mm/page-writeback.c | 649 +++++++++++++++++++++-----------------
mm/readahead.c | 2
mm/rmap.c | 2
mm/truncate.c | 25 +
mm/vmscan.c | 28 -
69 files changed, 3003 insertions(+), 1556 deletions(-)

--
tejun

[L] http://lkml.kernel.org/g/1427086499-15657-1-git-send-email-tj@kernel.org
[1] http://lkml.kernel.org/g/20150323041848.GA8991@htj.duckdns.org