Re: [PATCH v4] mm: oom: introduce cpuset oom

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Hi,

On 2023/8/17 16:40, Gang Li wrote:
On 2023/4/11 22:36, Michal Hocko wrote:
I believe it still wouldn't hurt to be more specific here.
CONSTRAINT_CPUSET is rather obscure. Looking at this just makes my head
spin.
         /* Check this allocation failure is caused by cpuset's wall function */
         for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
                         highest_zoneidx, oc->nodemask)
                 if (!cpuset_zone_allowed(zone, oc->gfp_mask))
                         cpuset_limited = true;
> Does this even work properly and why? prepare_alloc_pages sets
oc->nodemask to current->mems_allowed but the above gives us
cpuset_limited only if there is at least one zone/node that is not
oc->nodemask compatible. So it seems like this wouldn't ever get set
unless oc->nodemask got reset somewhere. This is a maze indeed.Is there

In __alloc_pages:
```
/*
  * Restore the original nodemask if it was potentially replaced with
  * &cpuset_current_mems_allowed to optimize the fast-path attempt.
  */
ac.nodemask = nodemask;
page = __alloc_pages_slowpath(alloc_gfp, order, &ac);

```

__alloc_pages set ac.nodemask back to mempolicy before call
__alloc_pages_slowpath.


any reason why we cannot rely on __GFP_HARWALL here? Or should we

In prepare_alloc_pages:
```
if (cpusets_enabled()) {
     *alloc_gfp |= __GFP_HARDWALL;
     ...
}
```

Since __GFP_HARDWALL is set as long as cpuset is enabled, I think we can
use it to determine if we are under the constraint of CPUSET.


We have two nodemasks: one from the parameters of __alloc_pages and
another from cpuset. If the node allowed by the parameters of
__alloc_pages is not allowed by cpuset, it means that this page
allocation is constrained by cpuset, and thus CONSTRAINT_CPUSET can be
returned.

I guess this piece of code is reasonable and we can keep the
code as it is.

Thanks,
Gang Li.




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