[Devel] Re: [PATCH 00/10] memcg: per cgroup dirty page accounting

[Balbir Singh]

* Greg Thelen <gthelen at google.com> [2010-10-03 23:57:55]:

> This patch set provides the ability for each cgroup to have independent dirty
> page limits.
> 
> Limiting dirty memory is like fixing the max amount of dirty (hard to reclaim)
> page cache used by a cgroup.  So, in case of multiple cgroup writers, they will
> not be able to consume more than their designated share of dirty pages and will
> be forced to perform write-out if they cross that limit.
> 
> These patches were developed and tested on mmotm 2010-09-28-16-13.  The patches
> are based on a series proposed by Andrea Righi in Mar 2010.
> 
> Overview:
> - Add page_cgroup flags to record when pages are dirty, in writeback, or nfs
>   unstable.
> - Extend mem_cgroup to record the total number of pages in each of the 
>   interesting dirty states (dirty, writeback, unstable_nfs).  
> - Add dirty parameters similar to the system-wide  /proc/sys/vm/dirty_*
>   limits to mem_cgroup.  The mem_cgroup dirty parameters are accessible
>   via cgroupfs control files.
> - Consider both system and per-memcg dirty limits in page writeback when
>   deciding to queue background writeback or block for foreground writeback.
> 
> Known shortcomings:
> - When a cgroup dirty limit is exceeded, then bdi writeback is employed to
>   writeback dirty inodes.  Bdi writeback considers inodes from any cgroup, not
>   just inodes contributing dirty pages to the cgroup exceeding its limit.  

I suspect this means that we'll need a bdi controller in the I/O
controller spectrum or make writeback cgroup aware.

> 
> Performance measurements:
> - kernel builds are unaffected unless run with a small dirty limit.
> - all data collected with CONFIG_CGROUP_MEM_RES_CTLR=y.
> - dd has three data points (in secs) for three data sizes (100M, 200M, and 1G).  
>   As expected, dd slows when it exceed its cgroup dirty limit.
> 
>                kernel_build          dd
> mmotm             2:37        0.18, 0.38, 1.65
>   root_memcg
> 
> mmotm             2:37        0.18, 0.35, 1.66
>   non-root_memcg
> 
> mmotm+patches     2:37        0.18, 0.35, 1.68
>   root_memcg
> 
> mmotm+patches     2:37        0.19, 0.35, 1.69
>   non-root_memcg
> 
> mmotm+patches     2:37        0.19, 2.34, 22.82
>   non-root_memcg
>   150 MiB memcg dirty limit
> 
> mmotm+patches     3:58        1.71, 3.38, 17.33
>   non-root_memcg
>   1 MiB memcg dirty limit
> 
> Greg Thelen (10):
>   memcg: add page_cgroup flags for dirty page tracking
>   memcg: document cgroup dirty memory interfaces
>   memcg: create extensible page stat update routines
>   memcg: disable local interrupts in lock_page_cgroup()
>   memcg: add dirty page accounting infrastructure
>   memcg: add kernel calls for memcg dirty page stats
>   memcg: add dirty limits to mem_cgroup
>   memcg: add cgroupfs interface to memcg dirty limits
>   writeback: make determine_dirtyable_memory() static.
>   memcg: check memcg dirty limits in page writeback
> 
>  Documentation/cgroups/memory.txt |   37 ++++
>  fs/nfs/write.c                   |    4 +
>  include/linux/memcontrol.h       |   78 +++++++-
>  include/linux/page_cgroup.h      |   31 +++-
>  include/linux/writeback.h        |    2 -
>  mm/filemap.c                     |    1 +
>  mm/memcontrol.c                  |  426 ++++++++++++++++++++++++++++++++++----
>  mm/page-writeback.c              |  211 ++++++++++++-------
>  mm/rmap.c                        |    4 +-
>  mm/truncate.c                    |    1 +
>  10 files changed, 672 insertions(+), 123 deletions(-)
> 
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> 

-- 
	Three Cheers,
	Balbir
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