Re: [PATCH v5 0/6] workload-specific and memory pressure-driven zswap writeback

[Chris Li]

Hi Nhat,

Sorry for being late to the party. I want to take a look at your patches series.
However I wasn't able to "git am" your patches series cleanly on current
mm-stable, mm-unstable or linux tip.

$ git am patches/v5_20231106_nphamcs_workload_specific_and_memory_pressure_driven_zswap_writeback.mbx
Applying: list_lru: allows explicit memcg and NUMA node selection
Applying: memcontrol: allows mem_cgroup_iter() to check for onlineness
Applying: zswap: make shrinking memcg-aware (fix)
error: patch failed: mm/zswap.c:174
error: mm/zswap.c: patch does not apply
Patch failed at 0003 zswap: make shrinking memcg-aware (fix)

What is the base of your patches? A git hash or a branch I can pull
from would be
nice.

Thanks

Chris

On Mon, Nov 6, 2023 at 10:32 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
> Changelog:
> v5:
>    * Replace reference getting with an rcu_read_lock() section for
>      zswap lru modifications (suggested by Yosry)
>    * Add a new prep patch that allows mem_cgroup_iter() to return
>      online cgroup.
>    * Add a callback that updates pool->next_shrink when the cgroup is
>      offlined (suggested by Yosry Ahmed, Johannes Weiner)
> v4:
>    * Rename list_lru_add to list_lru_add_obj and __list_lru_add to
>      list_lru_add (patch 1) (suggested by Johannes Weiner and
>          Yosry Ahmed)
>    * Some cleanups on the memcg aware LRU patch (patch 2)
>      (suggested by Yosry Ahmed)
>    * Use event interface for the new per-cgroup writeback counters.
>      (patch 3) (suggested by Yosry Ahmed)
>    * Abstract zswap's lruvec states and handling into
>      zswap_lruvec_state (patch 5) (suggested by Yosry Ahmed)
> v3:
>    * Add a patch to export per-cgroup zswap writeback counters
>    * Add a patch to update zswap's kselftest
>    * Separate the new list_lru functions into its own prep patch
>    * Do not start from the top of the hierarchy when encounter a memcg
>      that is not online for the global limit zswap writeback (patch 2)
>      (suggested by Yosry Ahmed)
>    * Do not remove the swap entry from list_lru in
>      __read_swapcache_async() (patch 2) (suggested by Yosry Ahmed)
>    * Removed a redundant zswap pool getting (patch 2)
>      (reported by Ryan Roberts)
>    * Use atomic for the nr_zswap_protected (instead of lruvec's lock)
>      (patch 5) (suggested by Yosry Ahmed)
>    * Remove the per-cgroup zswap shrinker knob (patch 5)
>      (suggested by Yosry Ahmed)
> v2:
>    * Fix loongarch compiler errors
>    * Use pool stats instead of memcg stats when !CONFIG_MEMCG_KEM
>
> There are currently several issues with zswap writeback:
>
> 1. There is only a single global LRU for zswap, making it impossible to
>    perform worload-specific shrinking - an memcg under memory pressure
>    cannot determine which pages in the pool it owns, and often ends up
>    writing pages from other memcgs. This issue has been previously
>    observed in practice and mitigated by simply disabling
>    memcg-initiated shrinking:
>
>    https://lore.kernel.org/all/20230530232435.3097106-1-nphamcs@xxxxxxxxx/T/#u
>
>    But this solution leaves a lot to be desired, as we still do not
>    have an avenue for an memcg to free up its own memory locked up in
>    the zswap pool.
>
> 2. We only shrink the zswap pool when the user-defined limit is hit.
>    This means that if we set the limit too high, cold data that are
>    unlikely to be used again will reside in the pool, wasting precious
>    memory. It is hard to predict how much zswap space will be needed
>    ahead of time, as this depends on the workload (specifically, on
>    factors such as memory access patterns and compressibility of the
>    memory pages).
>
> This patch series solves these issues by separating the global zswap
> LRU into per-memcg and per-NUMA LRUs, and performs workload-specific
> (i.e memcg- and NUMA-aware) zswap writeback under memory pressure. The
> new shrinker does not have any parameter that must be tuned by the
> user, and can be opted in or out on a per-memcg basis.
>
> As a proof of concept, we ran the following synthetic benchmark:
> build the linux kernel in a memory-limited cgroup, and allocate some
> cold data in tmpfs to see if the shrinker could write them out and
> improved the overall performance. Depending on the amount of cold data
> generated, we observe from 14% to 35% reduction in kernel CPU time used
> in the kernel builds.
>
> Domenico Cerasuolo (3):
>   zswap: make shrinking memcg-aware
>   mm: memcg: add per-memcg zswap writeback stat
>   selftests: cgroup: update per-memcg zswap writeback selftest
>
> Nhat Pham (3):
>   list_lru: allows explicit memcg and NUMA node selection
>   memcontrol: allows mem_cgroup_iter() to check for onlineness
>   zswap: shrinks zswap pool based on memory pressure
>
>  Documentation/admin-guide/mm/zswap.rst      |   7 +
>  drivers/android/binder_alloc.c              |   5 +-
>  fs/dcache.c                                 |   8 +-
>  fs/gfs2/quota.c                             |   6 +-
>  fs/inode.c                                  |   4 +-
>  fs/nfs/nfs42xattr.c                         |   8 +-
>  fs/nfsd/filecache.c                         |   4 +-
>  fs/xfs/xfs_buf.c                            |   6 +-
>  fs/xfs/xfs_dquot.c                          |   2 +-
>  fs/xfs/xfs_qm.c                             |   2 +-
>  include/linux/list_lru.h                    |  46 ++-
>  include/linux/memcontrol.h                  |   9 +-
>  include/linux/mmzone.h                      |   2 +
>  include/linux/vm_event_item.h               |   1 +
>  include/linux/zswap.h                       |  27 +-
>  mm/list_lru.c                               |  48 ++-
>  mm/memcontrol.c                             |  20 +-
>  mm/mmzone.c                                 |   1 +
>  mm/shrinker.c                               |   4 +-
>  mm/swap.h                                   |   3 +-
>  mm/swap_state.c                             |  26 +-
>  mm/vmscan.c                                 |  26 +-
>  mm/vmstat.c                                 |   1 +
>  mm/workingset.c                             |   4 +-
>  mm/zswap.c                                  | 430 +++++++++++++++++---
>  tools/testing/selftests/cgroup/test_zswap.c |  74 ++--
>  26 files changed, 625 insertions(+), 149 deletions(-)
>
> --
> 2.34.1
>