Messages in this thread | | | Date | Thu, 15 Aug 2019 12:56:19 -0700 | From | Tejun Heo <> | Subject | [PATCHSET v2] writeback, memcg: Implement foreign inode flushing |
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Hello,
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 flushing.
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-writeback-Generalize-and-expose-wb_completion.patch 0002-bdi-Add-bdi-id.patch 0003-writeback-Separate-out-wb_get_lookup-from-wb_get_create.patch 0004-writeback-memcg-Implement-cgroup_writeback_by_id.patch 0005-writeback-memcg-Implement-foreign-dirty-flushing.patch
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(-)
-- tejun
[1] http://lkml.kernel.org/r/20190803140155.181190-1-tj@kernel.org
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