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From: Tejun Heo <>
Subject: [PATCHSET v2] writeback, memcg: Implement foreign inode flushing
Date: Thu, 15 Aug 2019 12:56:19 -0700
Message-ID: <> (raw)


Changes from v1[1]:

* More comments explaining the parameters.

* 0003-writeback-Separate-out-wb_get_lookup-from-wb_get_create.patch
  added and avoid spuriously creating missing wbs for foreign

There's an inherent mismatch between memcg and writeback.  The former
trackes ownership per-page while the latter per-inode.  This was a
deliberate design decision because honoring per-page ownership in the
writeback path is complicated, may lead to higher CPU and IO overheads
and deemed unnecessary given that write-sharing an inode across
different cgroups isn't a common use-case.

Combined with inode majority-writer ownership switching, this works
well enough in most cases but there are some pathological cases.  For
example, let's say there are two cgroups A and B which keep writing to
different but confined parts of the same inode.  B owns the inode and
A's memory is limited far below B's.  A's dirty ratio can rise enough
to trigger balance_dirty_pages() sleeps but B's can be low enough to
avoid triggering background writeback.  A will be slowed down without
a way to make writeback of the dirty pages happen.

This patchset implements foreign dirty recording and foreign mechanism
so that when a memcg encounters a condition as above it can trigger
flushes on bdi_writebacks which can clean its pages.  Please see the
last patch for more details.

This patchset contains the following four patches.


0001-0004 are prep patches which expose wb_completion and implement
bdi->id and flushing by bdi and memcg IDs.

0005 implements foreign inode flushing.

Thanks.  diffstat follows.

 fs/fs-writeback.c                |  114 +++++++++++++++++++++++----------
 include/linux/backing-dev-defs.h |   23 ++++++
 include/linux/backing-dev.h      |    5 +
 include/linux/memcontrol.h       |   39 +++++++++++
 include/linux/writeback.h        |    2 
 mm/backing-dev.c                 |  120 +++++++++++++++++++++++++++++------
 mm/memcontrol.c                  |  132 +++++++++++++++++++++++++++++++++++++++
 mm/page-writeback.c              |    4 +
 8 files changed, 386 insertions(+), 53 deletions(-)



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Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-15 19:56 Tejun Heo [this message]
2019-08-15 19:57 ` [PATCH 1/5] writeback: Generalize and expose wb_completion Tejun Heo
2019-08-15 19:57 ` [PATCH 2/5] bdi: Add bdi->id Tejun Heo
2019-08-15 19:58 ` [PATCH 3/5] writeback: Separate out wb_get_lookup() from wb_get_create() Tejun Heo
2019-08-16 15:45   ` Jan Kara
2019-08-15 19:59 ` [PATCH 4/5] writeback, memcg: Implement cgroup_writeback_by_id() Tejun Heo
2019-08-16 15:47   ` Jan Kara
2019-08-21 21:02   ` [PATCH v3 " Tejun Heo
2019-08-15 19:59 ` [PATCH 5/5] writeback, memcg: Implement foreign dirty flushing Tejun Heo
2019-08-16 16:02   ` Jan Kara
2019-08-21 16:00     ` Tejun Heo
2019-08-21 16:04       ` Tejun Heo
2019-08-21 21:02   ` [PATCH v3 " Tejun Heo

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