Messages in this thread | | | Date | Thu, 17 Aug 2023 16:40:46 +0800 | Subject | Re: [PATCH v4] mm: oom: introduce cpuset oom | From | Gang Li <> |
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Apologize for the extremely delayed response. I was previously occupied with work unrelated to the Linux kernel.
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.
But I have a question: Why we always set __GFP_HARDWALL when cpuset is enabled, regardless of the value of cpuset.mem_hardwall?
Thanks, Gang Li
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