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SubjectRe: [PATCH] mm: page_alloc: update the COMPACT[STALL|FAIL] events properly
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On 2/6/2021 3:58 AM, David Rientjes wrote:
>> In the code, when COMPACT_SKIPPED is being returned, the page will
>> always be NULL. So, I'm not sure how much useful it is for the page ==
>> NULL check here. Or I failed to understand your point here?
>>
> Your code is short-circuiting the rest of __alloc_pages_direct_compact()
> where the return value is dictated by whether page is NULL or non-NULL.
> We can't leak a captured page if we are testing for it being NULL or
> non-NULL, which is what the rest of __alloc_pages_direct_compact() does
> *before* your change. So the idea was to add a check the page is actually
> NULL here since you are now relying on the return value of
> compact_zone_order() to be COMPACT_SKIPPED to infer page == NULL.
>
> I agree that's currently true in the code, I was trying to catch any
> errors where current->capture_control.page was non-NULL but
> try_to_compact_pages() returns COMPACT_SKIPPED. There's some complexity
> here.

Thanks for the detailed explanation. This looks fine to me. I will send
V2 with this information in the commit log.

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