linux-kernel - Re: [PATCH] mm: Add ARCH_FORCE_PAGE_BLOCK

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: <3230A277-7D1D-4329-B871-5E43967E6A00@nvidia.com>
Date: Thu, 01 May 2025 10:24:37 -0400
From: Zi Yan <ziy@...dia.com>
To: Juan Yescas <jyescas@...gle.com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, tjmercier@...gle.com, isaacmanjarres@...gle.com,
 surenb@...gle.com, kaleshsingh@...gle.com, Vlastimil Babka <vbabka@...e.cz>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 David Hildenbrand <david@...hat.com>, Mike Rapoport <rppt@...nel.org>,
 Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH] mm: Add ARCH_FORCE_PAGE_BLOCK_ORDER to select page block
 order

On 1 May 2025, at 1:25, Juan Yescas wrote:

> Problem: On large page size configurations (16KiB, 64KiB), the CMA
> alignment requirement (CMA_MIN_ALIGNMENT_BYTES) increases considerably,
> and this causes the CMA reservations to be larger than necessary.
> This means that system will have less available MIGRATE_UNMOVABLE and
> MIGRATE_RECLAIMABLE page blocks since MIGRATE_CMA can't fallback to them.
>
> The CMA_MIN_ALIGNMENT_BYTES increases because it depends on
> MAX_PAGE_ORDER which depends on ARCH_FORCE_MAX_ORDER. The value of
> ARCH_FORCE_MAX_ORDER increases on 16k and 64k kernels.
>
> For example, the CMA alignment requirement when:
>
> - CONFIG_ARCH_FORCE_MAX_ORDER default value is used
> - CONFIG_TRANSPARENT_HUGEPAGE is set:
>
> PAGE_SIZE | MAX_PAGE_ORDER | pageblock_order | CMA_MIN_ALIGNMENT_BYTES
> -----------------------------------------------------------------------
>    4KiB   |      10        |      10         |  4KiB * (2 ^ 10)  =  4MiB
>   16Kib   |      11        |      11         | 16KiB * (2 ^ 11) =  32MiB
>   64KiB   |      13        |      13         | 64KiB * (2 ^ 13) = 512MiB
>
> There are some extreme cases for the CMA alignment requirement when:
>
> - CONFIG_ARCH_FORCE_MAX_ORDER maximum value is set
> - CONFIG_TRANSPARENT_HUGEPAGE is NOT set:
> - CONFIG_HUGETLB_PAGE is NOT set
>
> PAGE_SIZE | MAX_PAGE_ORDER | pageblock_order |  CMA_MIN_ALIGNMENT_BYTES
> ------------------------------------------------------------------------
>    4KiB   |      15        |      15         |  4KiB * (2 ^ 15) = 128MiB
>   16Kib   |      13        |      13         | 16KiB * (2 ^ 13) = 128MiB
>   64KiB   |      13        |      13         | 64KiB * (2 ^ 13) = 512MiB
>
> This affects the CMA reservations for the drivers. If a driver in a
> 4KiB kernel needs 4MiB of CMA memory, in a 16KiB kernel, the minimal
> reservation has to be 32MiB due to the alignment requirements:
>
> reserved-memory {
>     ...
>     cma_test_reserve: cma_test_reserve {
>         compatible = "shared-dma-pool";
>         size = <0x0 0x400000>; /* 4 MiB */
>         ...
>     };
> };
>
> reserved-memory {
>     ...
>     cma_test_reserve: cma_test_reserve {
>         compatible = "shared-dma-pool";
>         size = <0x0 0x2000000>; /* 32 MiB */
>         ...
>     };
> };
>
> Solution: Add a new config ARCH_FORCE_PAGE_BLOCK_ORDER that
> allows to set the page block order. The maximum page block
> order will be given by ARCH_FORCE_MAX_ORDER.

Why not use a boot time parameter to change page block order?
Otherwise, you will need to maintain an additional kernel
binary for your use case.

--
Best Regards,
Yan, Zi