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

[Nhat Pham]

On Wed, Nov 8, 2023 at 11:46 AM Chris Li <chrisl@xxxxxxxxxx> wrote:
>
> 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)

Ah that was meant to be a fixlet - so that on top of the original
"zswap: make shrinking memcg-aware" patch. The intention was
to eventually squash it...

But this is getting a bit annoyingly confusing, I admit. I just rebased to
mm-unstable + squashed it all again, then sent one single replacement
patch:

[PATCH v5 3/6 REPLACE] zswap: make shrinking memcg-aware

Let me know if this still fails to apply. If not, I'll send the whole thing
again as v6! My sincerest apologies for the troubles and confusion :(


>
> 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
> >