Re: [External] Re: [PATCH V1] mm:page_alloc: fix the NULL ac->nodemask in __alloc_pages_slowpath()

[Zhongkun He]

On Thu, Aug 22, 2024 at 5:01 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Thu 22-08-24 16:38:42, Zhongkun He wrote:
> > I found a problem in my test machine that should_reclaim_retry() do
> > not get the right node if i set the cpuset.mems.
> > The should_reclaim_retry() and try_to_compact_pages() are iterating
> > nodes which are not allowed by cpusets and that makes the retry loop
> > happening more than unnecessary.
>
> I would update the problem description because from the above it is not
> really clear what the actual problem is.
>
> should_reclaim_retry is not ALLOC_CPUSET aware and that means that it
> considers reclaimability of NUMA nodes which are outside of the cpuset.
> If other nodes have a lot of reclaimable memory then should_reclaim_retry
> would instruct page allocator to retry even though there is no memory
> reclaimable on the cpuset nodemask. This is not really a huge problem
> because the number of retries without any reclaim progress is bound but
> it could be certainly improved. This is a cold path so this shouldn't
> really have a measurable impact on performance on most workloads.
>

Thanks for your description about this case.

> >
> > 1.Test step and the machines.
> > ------------
> > root@vm:/sys/fs/cgroup/test# numactl -H | grep size
> > node 0 size: 9477 MB
> > node 1 size: 10079 MB
> > node 2 size: 10079 MB
> > node 3 size: 10078 MB
> >
> > root@vm:/sys/fs/cgroup/test# cat cpuset.mems
> >     2
> >
> > root@vm:/sys/fs/cgroup/test# stress --vm 1 --vm-bytes 12g  --vm-keep
> > stress: info: [33430] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
> > stress: FAIL: [33430] (425) <-- worker 33431 got signal 9
> > stress: WARN: [33430] (427) now reaping child worker processes
> > stress: FAIL: [33430] (461) failed run completed in 2s
> >
> > 2. reclaim_retry_zone info:
> >
> > We can only alloc pages from node=2, but the reclaim_retry_zone is
> > node=0 and return true.
> >
> > root@vm:/sys/kernel/debug/tracing# cat trace
> > stress-33431   [001] ..... 13223.617311: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=1 wmark_check=1
> > stress-33431   [001] ..... 13223.617682: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=2 wmark_check=1
> > stress-33431   [001] ..... 13223.618103: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=3 wmark_check=1
> > stress-33431   [001] ..... 13223.618454: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=4 wmark_check=1
> > stress-33431   [001] ..... 13223.618770: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=5 wmark_check=1
> > stress-33431   [001] ..... 13223.619150: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=6 wmark_check=1
> > stress-33431   [001] ..... 13223.619510: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=7 wmark_check=1
> > stress-33431   [001] ..... 13223.619850: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=8 wmark_check=1
> > stress-33431   [001] ..... 13223.620171: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=9 wmark_check=1
> > stress-33431   [001] ..... 13223.620533: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=10 wmark_check=1
> > stress-33431   [001] ..... 13223.620894: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=11 wmark_check=1
> > stress-33431   [001] ..... 13223.621224: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=12 wmark_check=1
> > stress-33431   [001] ..... 13223.621551: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=13 wmark_check=1
> > stress-33431   [001] ..... 13223.621847: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=14 wmark_check=1
> > stress-33431   [001] ..... 13223.622200: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=15 wmark_check=1
> > stress-33431   [001] ..... 13223.622580: reclaim_retry_zone: node=0 zone=Normal   order=0 reclaimable=4260 available=1772019 min_wmark=5962 no_progress_loops=16 wmark_check=1
> >
>
> You can drop the following
>

OK.

> > 3. Root cause:
> > Nodemask usually comes from mempolicy in policy_nodemask(), which
> > is always NULL unless the memory policy is bind or prefer_many.
> >
> > nodemask = NULL
> > __alloc_pages_noprof()
> >       prepare_alloc_pages
> >               ac->nodemask = &cpuset_current_mems_allowed;
> >
> >       get_page_from_freelist()
> >
> >       ac.nodemask = nodemask;  /*set  NULL*/
> >
> >       __alloc_pages_slowpath() {
> >               f (!(alloc_flags & ALLOC_CPUSET) || reserve_flags) {
> >                       ac->nodemask = NULL;
> >                       ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
> >                                       ac->highest_zoneidx, ac->nodemask);
> >
> >               /* so ac.nodemask = NULL */
> >       }
> >
> > According to the function flow above, we do not have the memory limit to
> > follow cpuset.mems, so we need to add it.
> >
> > Test result:
> > Try 3 times with different cpuset.mems and alloc large memorys than that numa size.
> > echo 1 > cpuset.mems
> > stress --vm 1 --vm-bytes 12g --vm-hang 0
> > ---------------
> > echo 2 > cpuset.mems
> > stress --vm 1 --vm-bytes 12g --vm-hang 0
> > ---------------
> > echo 3 > cpuset.mems
> > stress --vm 1 --vm-bytes 12g --vm-hang 0
> >
> > The retry trace look like:
> > stress-2139    [003] .....   666.934104: reclaim_retry_zone: node=1 zone=Normal   order=0 reclaimable=7 available=7355 min_wmark=8598 no_progress_loops=1 wmark_check=0
> > stress-2204    [010] .....   695.447393: reclaim_retry_zone: node=2 zone=Normal   order=0 reclaimable=2 available=6916 min_wmark=8598 no_progress_loops=1 wmark_check=0
> > stress-2271    [008] .....   725.683058: reclaim_retry_zone: node=3 zone=Normal   order=0 reclaimable=17 available=8079 min_wmark=8597 no_progress_loops=1 wmark_check=0
> >
>
> And only keep this
>

OK.

> > With this patch, we can check the right node and get less retry in __alloc_pages_slowpath()
> > because there is nothing to do.
> >
> > V1:
> > Do the same with the page allocator using __cpuset_zone_allowed().
> >
> > Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
> > Signed-off-by: Zhongkun He <hezhongkun.hzk@xxxxxxxxxxxxx>
>
> With those changes you can add
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Thanks!
>
> > ---
> >  mm/compaction.c | 6 ++++++
> >  mm/page_alloc.c | 5 +++++
> >  2 files changed, 11 insertions(+)
> >
> > diff --git a/mm/compaction.c b/mm/compaction.c
> > index d1041fbce679..a2b16b08cbbf 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -23,6 +23,7 @@
> >  #include <linux/freezer.h>
> >  #include <linux/page_owner.h>
> >  #include <linux/psi.h>
> > +#include <linux/cpuset.h>
> >  #include "internal.h"
> >
> >  #ifdef CONFIG_COMPACTION
> > @@ -2822,6 +2823,11 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
> >                                       ac->highest_zoneidx, ac->nodemask) {
> >               enum compact_result status;
> >
> > +             if (cpusets_enabled() &&
> > +                     (alloc_flags & ALLOC_CPUSET) &&
> > +                     !__cpuset_zone_allowed(zone, gfp_mask))
> > +                             continue;
> > +
> >               if (prio > MIN_COMPACT_PRIORITY
> >                                       && compaction_deferred(zone, order)) {
> >                       rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 29608ca294cf..8a67d760b71a 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4128,6 +4128,11 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> >               unsigned long min_wmark = min_wmark_pages(zone);
> >               bool wmark;
> >
> > +             if (cpusets_enabled() &&
> > +                     (alloc_flags & ALLOC_CPUSET) &&
> > +                     !__cpuset_zone_allowed(zone, gfp_mask))
> > +                             continue;
> > +
> >               available = reclaimable = zone_reclaimable_pages(zone);
> >               available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
> >
> > --
> > 2.20.1
>
> --
> Michal Hocko
> SUSE Labs