Re: [mm-unstable v4 0/5] mm: memcg: subtree stats flushing and thresholds

[Bagas Sanjaya <bagasdotme@gmail.com>]

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On Wed, Nov 29, 2023 at 03:21:48AM +0000, Yosry Ahmed wrote:
> This series attempts to address shortages in today's approach for memcg
> stats flushing, namely occasionally stale or expensive stat reads. The
> series does so by changing the threshold that we use to decide whether
> to trigger a flush to be per memcg instead of global (patch 3), and then
> changing flushing to be per memcg (i.e. subtree flushes) instead of
> global (patch 5).
> 
> Patch 3 & 5 are the core of the series, and they include more details
> and testing results. The rest are either cleanups or prep work.
> 
> This series replaces the "memcg: more sophisticated stats flushing"
> series [1], which also replaces another series, in a long list of
> attempts to improve memcg stats flushing. It is not a new version of
> the same patchset as it is a completely different approach. This is
> based on collected feedback from discussions on lkml in all previous
> attempts. Hopefully, this is the final attempt.
> 
> There was a reported regression in v2 [2] for will-it-scale::fallocate
> benchmark. I believe this regression should not affect production
> workloads. This specific benchmark is allocating and freeing memory
> (using fallocate/ftruncate) at a rate that is much faster to make actual
> use of the memory. Testing this series on 100+ machines running
> production workloads did not show any practical regressions in page
> fault latency or allocation latency, but it showed great improvements in
> stats read time. I do not have numbers about the exact improvements for
> this series, but combined with another optimization for cgroup v1 [3] we
> see 5-10x improvements. A significant chunk of that is coming from the
> cgroup v1 optimization, but this series also made an improvement as
> reported by Domenico [4].
> 
> v3 -> v4:
> - Rebased on top of mm-unstable + "workload-specific and memory
>   pressure-driven zswap writeback" series to fix conflicts [5].
> 
> v3: https://lore.kernel.org/all/20231116022411.2250072-1-yosryahmed@google.com/
> 
> [1]https://lore.kernel.org/lkml/20230913073846.1528938-1-yosryahmed@google.com/
> [2]https://lore.kernel.org/lkml/202310202303.c68e7639-oliver.sang@intel.com/
> [3]https://lore.kernel.org/lkml/20230803185046.1385770-1-yosryahmed@google.com/
> [4]https://lore.kernel.org/lkml/CAFYChMv_kv_KXOMRkrmTN-7MrfgBHMcK3YXv0dPYEL7nK77e2A@mail.gmail.com/
> [5]https://lore.kernel.org/all/20231127234600.2971029-1-nphamcs@gmail.com/
> 
> Yosry Ahmed (5):
>   mm: memcg: change flush_next_time to flush_last_time
>   mm: memcg: move vmstats structs definition above flushing code
>   mm: memcg: make stats flushing threshold per-memcg
>   mm: workingset: move the stats flush into workingset_test_recent()
>   mm: memcg: restore subtree stats flushing
> 
>  include/linux/memcontrol.h |   8 +-
>  mm/memcontrol.c            | 272 +++++++++++++++++++++----------------
>  mm/vmscan.c                |   2 +-
>  mm/workingset.c            |  42 ++++--
>  4 files changed, 188 insertions(+), 136 deletions(-)
> 

No regressions when booting the kernel with this series applied.

Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>

-- 
An old man doll... just what I always wanted! - Clara

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