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

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Message-ID: <0f292735-4b13-417f-bc65-82cebd2040a3@linux.dev>
Date: Mon, 24 Nov 2025 17:27:23 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: Zhiheng Tao <junchuan.tzh@...group.com>
Cc: ziy@...dia.com, baolin.wang@...ux.alibaba.com, Liam.Howlett@...cle.com,
 npache@...hat.com, ryan.roberts@....com, dev.jain@....com,
 baohua@...nel.org, shy828301@...il.com, zokeefe@...gle.com,
 peterx@...hat.com, akpm@...ux-foundation.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, lorenzo.stoakes@...cle.com,
 "David Hildenbrand (Red Hat)" <david@...nel.org>
Subject: Re: [PATCH] mm/khugepaged: Fix skipping of alloc sleep after second
 failure



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