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.
