Re: [PATCH v8 0/6] workload-specific and memory pressure-driven zswap writeback

Bagas Sanjaya
2023-12-06T04:24:24Z

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On Thu, Nov 30, 2023 at 11:40:17AM -0800, Nhat Pham wrote:
> Changelog:
> v8:
> * Fixed a couple of build errors in the case of !CONFIG_MEMCG
> * Simplified the online memcg selection scheme for the zswap global
> limit reclaim (suggested by Michal Hocko and Johannes Weiner)
> (patch 2 and patch 3)
> * Added a new kconfig to allows users to enable zswap shrinker by
> default. (suggested by Johannes Weiner) (patch 6)
> v7:
> * Added the mem_cgroup_iter_online() function to the API for the new
> behavior (suggested by Andrew Morton) (patch 2)
> * Fixed a missing list_lru_del -> list_lru_del_obj (patch 1)
> v6:
> * Rebase on top of latest mm-unstable.
> * Fix/improve the in-code documentation of the new list_lru
> manipulation functions (patch 1)
> 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@gmail.com/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: implement mem_cgroup_tryget_online()
> zswap: shrinks zswap pool based on memory pressure
>
> Documentation/admin-guide/mm/zswap.rst | 10 +
> drivers/android/binder_alloc.c | 7 +-
> 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 | 54 ++-
> include/linux/memcontrol.h | 15 +
> include/linux/mmzone.h | 2 +
> include/linux/vm_event_item.h | 1 +
> include/linux/zswap.h | 27 +-
> mm/Kconfig | 14 +
> mm/list_lru.c | 48 ++-
> mm/memcontrol.c | 3 +
> mm/mmzone.c | 1 +
> mm/swap.h | 3 +-
> mm/swap_state.c | 26 +-
> mm/vmstat.c | 1 +
> mm/workingset.c | 4 +-
> mm/zswap.c | 456 +++++++++++++++++---
> tools/testing/selftests/cgroup/test_zswap.c | 74 ++--
> 25 files changed, 661 insertions(+), 125 deletions(-)
>

Carrying from v7,

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

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

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