Re: [RFC PATCH -next 0/7] Introduce heat-level memcg reclaim

[Chen Ridong <chenridong@huaweicloud.com>]

On 2026/1/20 21:42, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> The memcg LRU was originally introduced to improve scalability during
> global reclaim, but it only supports gen lru global reclaim and its
> implementation has become complex. Moreover, it has caused performance
> regressions when dealing with a large number of memory cgroups [1].
> 
> Previous attempts to remove memcg LRU by switching back to iteration
> implementation brought performance regression [3].
> 
> This series introduces a per-memcg heat level mechanism for reclaim,
> aiming to unify gen lru and traditional LRU global reclaim. The core
> idea is to track per-node per-memcg reclaim state, including heat,
> last_decay, and last_refault. Three reclaim heat levels are defined:
> cold, warm, and hot. Cold memcgs are reclaimed first; only if cold
> memcgs cannot reclaim enough pages, warm memcgs become eligible for
> reclaim. Hot memcgs are reclaimed last.
> 
> While the heat level design can be applied to all memcg reclaim scenarios,
> this series takes a conservative approach and initially applies it only
> to global reclaim. The first few patches introduce the heat level
> infrastructure and apply it to traditional LRU global reclaim. The
> subsequent patches gradually migrate gen lru global reclaim to the
> heat-level-based approach, with the final patch combining shrink_many
> into shrink_node_memcgs to complete the transition.
> 
> Performance results show significant improvements:
> 
> Traditional LRU results (2-hour run of test [2]):
> Throughput (number of requests)         before     after        Change
> Total                                   1,734,169  2,353,717    +35%
> 
> Gen LRU results (24-hour run of test [2]):
> Throughput (number of requests)         before     after        Change
> Total                                   22,879,701 25,331,956   +10%
> 
> The performance tests are based on next branch commit:
> commit ef0d146624b0 ("Add linux-next specific files for 20251219")
> 
> This series has been rebased on next-20260119:
> commit d08c85ac8894 ("Add linux-next specific files for 20260119")
> 
> [1] https://lore.kernel.org/r/20251126171513.GC135004@cmpxchg.org
> [2] https://lore.kernel.org/r/20221222041905.2431096-7-yuzhao@google.com
> [3] https://lore.kernel.org/lkml/20251224073032.161911-1-chenridong@huaweicloud.com/
> 
> Chen Ridong (7):
>   vmscan: add memcg heat level for reclaim
>   mm/mglru: make calls to flush_reclaim_state() similar for MGLRU and
>     non-MGLRU
>   mm/mglru: rename should_abort_scan to lru_gen_should_abort_scan
>   mm/mglru: extend lru_gen_shrink_lruvec to support root reclaim
>   mm/mglru: combine shrink_many into shrink_node_memcgs
>   mm/mglru: remove memcg disable handling from lru_gen_shrink_node
>   mm/mglru: remove memcg lru
> 
>  Documentation/mm/multigen_lru.rst |  30 --
>  include/linux/memcontrol.h        |   7 +
>  include/linux/mmzone.h            |  89 -----
>  mm/memcontrol-v1.c                |   6 -
>  mm/memcontrol.c                   |   7 +-
>  mm/mm_init.c                      |   1 -
>  mm/vmscan.c                       | 547 ++++++++++++------------------
>  7 files changed, 231 insertions(+), 456 deletions(-)
> 

Hi, Johannes and Shakeel,

I would appreciate it if you could share your thoughts on this series.

-- 
Best regards,
Ridong