linux-kernel - Re: [RFC PATCH] mm/page_alloc: Add PCP list for THP CMA

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: <ee7ba479-4917-4d83-8130-8c247c08d2d0@suse.cz>
Date: Tue, 5 Aug 2025 23:09:12 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Juan Yescas <jyescas@...gle.com>
Cc: David Hildenbrand <david@...hat.com>, akash.tyagi@...iatek.com,
 Andrew Morton <akpm@...ux-foundation.org>,
 angelogioacchino.delregno@...labora.com, hannes@...xchg.org,
 Brendan Jackman <jackmanb@...gle.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
 Linux Memory Management List <linux-mm@...ck.org>, matthias.bgg@...il.com,
 Michal Hocko <mhocko@...e.com>, Suren Baghdasaryan <surenb@...gle.com>,
 wsd_upstream@...iatek.com, Zi Yan <ziy@...dia.com>,
 Kalesh Singh <kaleshsingh@...gle.com>, "T.J. Mercier"
 <tjmercier@...gle.com>, Isaac Manjarres <isaacmanjarres@...gle.com>
Subject: Re: [RFC PATCH] mm/page_alloc: Add PCP list for THP CMA

On 8/5/25 19:12, Juan Yescas wrote:
> On Tue, Aug 5, 2025 at 2:52 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>> >
>> > Thanks David for the quick overview.
>> >
>> >> I still have no clue what this patch here tried to solve: it doesn't
>> >> make any sense.
>> >>
>> >
>> > The story started with this out of tree patch that is part of Android.
>> >
>> > https://lore.kernel.org/lkml/cover.1604282969.git.cgoldswo@codeaurora.org/T/#u
>> >
>> > This patch introduced the __GFP_CMA flag that allocates pages from
>> > MIGRATE_MOVABLE
>> > or MIGRATE_CMA.
>>
>> What kinds of allocations would then use __GFP_CMA?
> 
> The __GFP_CMA allocations are used to allocate userspace anonymous memory. This
> was done initially in the alloc_zeroed_user_highpage_movable()
> function, now it is done
> in vma_alloc_zeroed_movable_folio().

So that means you perceive the risk of anonymous memory being temporarily
pinned and thwarting a alloc_contig_pages() device CMA allocation lower than
for file pages? The pinning can be a gup(), or a compaction migrating the
page, etc...