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/[email protected]/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
Hi Nhat,
I want want to share the high level feedback we discussed here in the
mailing list as well.
It is my observation that each memcg LRU list can't compare the page
time order with other memcg.
It works great when the leaf level memcg hits the memory limit and you
want to reclaim from that memcg.
It works less well on the global memory pressure you need to reclaim
from all memcg. You kind of have to
scan each all child memcg to find out the best page to shrink from. It
is less effective to get to the most desirable page quickly.
This can benefit from a design similar to MGLRU. This idea is
suggested by Yu Zhao, credit goes to him not me.
In other words, the current patch is similar to the memcg page list
pre MGLRU world. We can have a MRLRU
like per memcg zswap shrink list.
Chris
On Wed, Nov 8, 2023 at 6:10 PM Chris Li <[email protected]> wrote:
>
> On Wed, Nov 8, 2023 at 4:28 PM Nhat Pham <[email protected]> wrote:
> >
> > Hmm my guess is that I probably sent this out based on an outdated
> > mm-unstable. There has since been a new zswap selftest merged
> > to mm-unstable (written by no other than myself - oh the irony), so
> > maybe it does not apply cleanly anymore with git am.
>
> $ git am -3 patches/zswap-pool-lru/0005
> Applying: selftests: cgroup: update per-memcg zswap writeback selftest
> Using index info to reconstruct a base tree...
> M tools/testing/selftests/cgroup/test_zswap.c
> Falling back to patching base and 3-way merge...
> Auto-merging tools/testing/selftests/cgroup/test_zswap.c
> $ git am -3 patches/zswap-pool-lru/0006
> Applying: zswap: shrinks zswap pool based on memory pressure
> error: sha1 information is lacking or useless (mm/zswap.c).
> error: could not build fake ancestor
> Patch failed at 0001 zswap: shrinks zswap pool based on memory pressure
> hint: Use 'git am --show-current-patch=diff' to see the failed patch
> When you have resolved this problem, run "git am --continue".
> If you prefer to skip this patch, run "git am --skip" instead.
> To restore the original branch and stop patching, run "git am --abort".
>
> I was able to resolve the conflict on patch 6 by hand though. So I am good now.
>
> Thanks
>
> Chris
On Thu, Nov 16, 2023 at 4:57 PM Chris Li <[email protected]> wrote:
>
> Hi Nhat,
>
> I want want to share the high level feedback we discussed here in the
> mailing list as well.
>
> It is my observation that each memcg LRU list can't compare the page
> time order with other memcg.
> It works great when the leaf level memcg hits the memory limit and you
> want to reclaim from that memcg.
> It works less well on the global memory pressure you need to reclaim
> from all memcg. You kind of have to
> scan each all child memcg to find out the best page to shrink from. It
> is less effective to get to the most desirable page quickly.
>
> This can benefit from a design similar to MGLRU. This idea is
> suggested by Yu Zhao, credit goes to him not me.
> In other words, the current patch is similar to the memcg page list
> pre MGLRU world. We can have a MRLRU
> like per memcg zswap shrink list.
I was gonna summarize the points myself :P But thanks for doing this.
It's your idea so you're more qualified to explain this anyway ;)
I absolutely agree that having a generation-aware cgroup-aware
NUMA-aware LRU is the future way to go. Currently, IIUC, the reclaim logic
selects cgroups in a round-robin-ish manner. It's "fair" in this perspective,
but I also think it's not ideal. As we have discussed, the current list_lru
infrastructure only take into account intra-cgroup relative recency, not
inter-cgroup relative recency. The recently proposed time-based zswap
reclaim mechanism will provide us with a source of information, but the
overhead of using this might be too high - and it's very zswap-specific.
Maybe after this, we should improve zswap reclaim (and perhaps all
list_lru users) by adding generations to list_lru then take generations
into account in the vmscan code. This patch series could be merged
as-is, and once we make list_lru generation-aware, zswap shrinker
will automagically be improved (along with all other list_lru/shrinker
users).
I don't know enough about the current design of MGLRU to comment
too much further, but let me know if this makes sense, and if you have
objections/other ideas.
And if you have other documentations for MGLRU than its code, could
you please let me know? I'm struggling to find more details about this.
>
>
> Chris
>
> On Wed, Nov 8, 2023 at 6:10 PM Chris Li <[email protected]> wrote:
> >
> > On Wed, Nov 8, 2023 at 4:28 PM Nhat Pham <[email protected]> wrote:
> > >
> > > Hmm my guess is that I probably sent this out based on an outdated
> > > mm-unstable. There has since been a new zswap selftest merged
> > > to mm-unstable (written by no other than myself - oh the irony), so
> > > maybe it does not apply cleanly anymore with git am.
> >
> > $ git am -3 patches/zswap-pool-lru/0005
> > Applying: selftests: cgroup: update per-memcg zswap writeback selftest
> > Using index info to reconstruct a base tree...
> > M tools/testing/selftests/cgroup/test_zswap.c
> > Falling back to patching base and 3-way merge...
> > Auto-merging tools/testing/selftests/cgroup/test_zswap.c
> > $ git am -3 patches/zswap-pool-lru/0006
> > Applying: zswap: shrinks zswap pool based on memory pressure
> > error: sha1 information is lacking or useless (mm/zswap.c).
> > error: could not build fake ancestor
> > Patch failed at 0001 zswap: shrinks zswap pool based on memory pressure
> > hint: Use 'git am --show-current-patch=diff' to see the failed patch
> > When you have resolved this problem, run "git am --continue".
> > If you prefer to skip this patch, run "git am --skip" instead.
> > To restore the original branch and stop patching, run "git am --abort".
> >
> > I was able to resolve the conflict on patch 6 by hand though. So I am good now.
> >
> > Thanks
> >
> > Chris
On Fri, Nov 17, 2023 at 8:23 AM Nhat Pham <[email protected]> wrote:
>
> On Thu, Nov 16, 2023 at 4:57 PM Chris Li <[email protected]> wrote:
> >
> > Hi Nhat,
> >
> > I want want to share the high level feedback we discussed here in the
> > mailing list as well.
> >
> > It is my observation that each memcg LRU list can't compare the page
> > time order with other memcg.
> > It works great when the leaf level memcg hits the memory limit and you
> > want to reclaim from that memcg.
> > It works less well on the global memory pressure you need to reclaim
> > from all memcg. You kind of have to
> > scan each all child memcg to find out the best page to shrink from. It
> > is less effective to get to the most desirable page quickly.
> >
> > This can benefit from a design similar to MGLRU. This idea is
> > suggested by Yu Zhao, credit goes to him not me.
> > In other words, the current patch is similar to the memcg page list
> > pre MGLRU world. We can have a MRLRU
> > like per memcg zswap shrink list.
>
> I was gonna summarize the points myself :P But thanks for doing this.
> It's your idea so you're more qualified to explain this anyway ;)
>
> I absolutely agree that having a generation-aware cgroup-aware
> NUMA-aware LRU is the future way to go. Currently, IIUC, the reclaim logic
> selects cgroups in a round-robin-ish manner. It's "fair" in this perspective,
> but I also think it's not ideal. As we have discussed, the current list_lru
> infrastructure only take into account intra-cgroup relative recency, not
> inter-cgroup relative recency. The recently proposed time-based zswap
> reclaim mechanism will provide us with a source of information, but the
> overhead of using this might be too high - and it's very zswap-specific.
>
> Maybe after this, we should improve zswap reclaim (and perhaps all
> list_lru users) by adding generations to list_lru then take generations
> into account in the vmscan code. This patch series could be merged
> as-is, and once we make list_lru generation-aware, zswap shrinker
> will automagically be improved (along with all other list_lru/shrinker
> users).
>
> I don't know enough about the current design of MGLRU to comment
> too much further, but let me know if this makes sense, and if you have
> objections/other ideas.
>
> And if you have other documentations for MGLRU than its code, could
> you please let me know? I'm struggling to find more details about this.
>
This could be a good place to start:
https://www.youtube.com/watch?v=9HvJfN21H9Y
On Fri, Nov 17, 2023 at 8:23 AM Nhat Pham <[email protected]> wrote:
>
> On Thu, Nov 16, 2023 at 4:57 PM Chris Li <[email protected]> wrote:
> >
> > Hi Nhat,
> >
> > I want want to share the high level feedback we discussed here in the
> > mailing list as well.
> >
> > It is my observation that each memcg LRU list can't compare the page
> > time order with other memcg.
> > It works great when the leaf level memcg hits the memory limit and you
> > want to reclaim from that memcg.
> > It works less well on the global memory pressure you need to reclaim
> > from all memcg. You kind of have to
> > scan each all child memcg to find out the best page to shrink from. It
> > is less effective to get to the most desirable page quickly.
> >
> > This can benefit from a design similar to MGLRU. This idea is
> > suggested by Yu Zhao, credit goes to him not me.
> > In other words, the current patch is similar to the memcg page list
> > pre MGLRU world. We can have a MRLRU
> > like per memcg zswap shrink list.
>
> I was gonna summarize the points myself :P But thanks for doing this.
> It's your idea so you're more qualified to explain this anyway ;)
The MGLRU like shrinker was Zhao Yu's idea. I just observe the problem.
>
> I absolutely agree that having a generation-aware cgroup-aware
> NUMA-aware LRU is the future way to go. Currently, IIUC, the reclaim logic
> selects cgroups in a round-robin-ish manner. It's "fair" in this perspective,
> but I also think it's not ideal. As we have discussed, the current list_lru
> infrastructure only take into account intra-cgroup relative recency, not
> inter-cgroup relative recency. The recently proposed time-based zswap
> reclaim mechanism will provide us with a source of information, but the
> overhead of using this might be too high - and it's very zswap-specific.
I don't mind it is zswap-specific, as long as it is effective.
The overhead has two folds:
1) memory overhead on storing timestamps on per compressed page.
2) cpu overhead for reading timestamps.
Using MGLRU likely have advantage over time stamps on both memory and
cpu. The generation can use fewer bits and doesn't require reading
time on every page.
> Maybe after this, we should improve zswap reclaim (and perhaps all
> list_lru users) by adding generations to list_lru then take generations
> into account in the vmscan code. This patch series could be merged
One high level idea is that we can get the page generation in the
MGLRU before it gets into zswap. Just retain the generation into the
zpool LRU somehow.
> as-is, and once we make list_lru generation-aware, zswap shrinker
> will automagically be improved (along with all other list_lru/shrinker
> users).
I don't think it will automatically improve, you will need to rewrite
a lot of code in the shrinker as well to best use MGLRU zpool.
>
> I don't know enough about the current design of MGLRU to comment
> too much further, but let me know if this makes sense, and if you have
> objections/other ideas.
Taking the step by step approach is fine by me as long as we are
making steady progress towards the better end goal.
>
> And if you have other documentations for MGLRU than its code, could
> you please let me know? I'm struggling to find more details about this.
I would need to learn MGLRU myself. We can share and compare notes
when we get to it.
Chris