Re: [PATCH] mm/khugepaged: Fix skipping of alloc sleep after second failure

[Lance Yang <lance.yang@linux.dev>]

On 2025/11/24 17:14, David Hildenbrand (Red Hat) wrote:
> On 11/24/25 07:19, Zhiheng Tao wrote:
>> In khugepaged_do_scan(), two consecutive allocation failures cause
>> the logic to skip the dedicated 60s throttling sleep
>> (khugepaged_alloc_sleep_millisecs), forcing a fallback to the
>> shorter 10s scanning interval via the outer loop
>>
>> Since fragmentation is unlikely to resolve in 10s, this results in
>> wasted CPU cycles on immediate retries.
> 
> Why shouldn't memory comapction be able to compact a single THP in 10s?
> 
> Why should it resolve in 60s?
> 
>>
>> Reorder the failure logic to ensure khugepaged_alloc_sleep() is
>> always called on each allocation failure.
>>
>> Fixes: c6a7f445a272 ("mm: khugepaged: don't carry huge page to the 
>> next loop for !CONFIG_NUMA")
> 
> What are we fixing here? This sounds like a change that might be better 
> on some systems, but worse on others?

Seems like we're not honoring khugepaged_alloc_sleep_millisecs on the
second allocation failure... but is that actually a problem?

> 
> We really need more information on when/how an issue was hit, and how 
> this patch here really moves the needle in any way.

+1