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

[Michal Hocko <mhocko@suse.com>]

On Thu 22-08-24 11:15:34, Zhongkun He wrote:
> On Wed, Aug 21, 2024 at 11:00 PM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Wed 21-08-24 21:59:00, 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
> > >
> > > 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
> >
> > OK, so the test gets killed as expected.
> >
> > > 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
> >
> > Are you suggesting that the problem is that should_reclaim_retry is
> > iterating nodes which are not allowed by cpusets and that makes the
> > retry loop happening more than unnecessary?
> 
> Yes, exactly.
> 
> >
> > Is there any reason why you haven't done the same that the page
> > allocator does in this case?
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 28f80daf5c04..cbf09c0e3b8a 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4098,6 +4098,11 @@ 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);
> >
> 
> That was my original version,  but I found that the problem exists in
> other places.
> Please see the function flow below.
> 
> __alloc_pages_slowpath:
> 
>   get_page_from_freelist
>      __cpuset_zone_allowed /* check the node */
> 
>   __alloc_pages_direct_reclaim
>      shrink_zones
>         cpuset_zone_allowed（）/* check the node */
> 
>  __alloc_pages_direct_compact
>    try_to_compact_pages
>        /* do not check the cpuset_zone_allowed（）*/
> 
>   should_reclaim_retry
>   /* do not check the cpuset_zone_allowed（）*/
> 
>   should_compact_retry
>       compaction_zonelist_suitable
>           /* do not check the cpuset_zone_allowed（）*/
> 
> Should we add __cpuset_zone_allowed() checks in the three functions
> listed above,
> or should we set the nodemask in __alloc_pages_slowpath()  if it is empty
> and the request comes from user space?

cpuset integration into the page allocator is rather complex (check
ALLOC_CPUSET) use. Reviewing your change is not an easy task to make
sure all the subtlety is preserved. Therefore I would suggest addressing
the specific issue you have found.

-- 
Michal Hocko
SUSE Labs