Re: [RFC PATCH] mm, oom: introduce vm.sacrifice_hugepage_on_oom

[David Hildenbrand]

On 16.02.21 04:07, Eiichi Tsukata wrote:
> Hugepages can be preallocated to avoid unpredictable allocation latency.
> If we run into 4k page shortage, the kernel can trigger OOM even though
> there were free hugepages. When OOM is triggered by user address page
> fault handler, we can use oom notifier to free hugepages in user space
> but if it's triggered by memory allocation for kernel, there is no way
> to synchronously handle it in user space.
>
> This patch introduces a new sysctl vm.sacrifice_hugepage_on_oom. If
> enabled, it first tries to free a hugepage if available before invoking
> the oom-killer. The default value is disabled not to change the current
> behavior.

In addition to the other comments, some more thoughts:

What if you're low on kernel memory but you end up freeing huge pages 
residing in ZONE_MOVABLE? IOW, this is not zone aware.

--
Thanks,

David / dhildenb