linux-kernel - Re: [PATCH v1] mm/huge_memory: fix shrinking of all-zero THPs with max_ptes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b56b43c1-d49d-4302-a171-9b00bf9cfa54@redhat.com>
Date: Fri, 5 Sep 2025 16:58:56 +0200
From: David Hildenbrand <david@...hat.com>
To: Usama Arif <usamaarif642@...il.com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>
Subject: Re: [PATCH v1] mm/huge_memory: fix shrinking of all-zero THPs with
 max_ptes_none default

On 05.09.25 16:53, Usama Arif wrote:
> 
> 
> On 05/09/2025 15:46, David Hildenbrand wrote:
>> [...]
>>
>>>
>>> The reason I did this is for the case if you change max_ptes_none after the THP is added
>>> to deferred split list but *before* memory pressure, i.e. before the shrinker runs,
>>> so that its considered for splitting.
>>
>> Yeah, I was assuming that was the reason why the shrinker is enabled as default.
>>
>> But in any sane system, the admin would enable the shrinker early. If not, we can look into handling it differently.
> 
> Yes, I do this as well, i.e. have a low value from the start.
> 
> Does it make sense to disable shrinker if max_ptes_none is 511? It wont shrink
> the usecase you are describing below, but we wont encounter the increased CPU usage.>

I don't really see why we should do that.

If the shrinker is a problem than the shrinker should be disabled. But 
if it is enabled, we should be shrinking as documented.

Without more magic around our THP toggles (we want less) :)

Shrinking happens when we are under memory pressure, so I am not really 
sure how relevant the scanning bit is, and if it is relevant enought to 
change the shrinker default.

-- 
Cheers

David / dhildenb