linux-kernel - Re: [RFC PATCH 13/15] mm: convert MAX_ORDER sized static arrays to dynamic ones.

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]

Date:   Thu, 05 Aug 2021 15:58:32 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Christian König <christian.koenig@....com>
Cc:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        linux-kernel@...r.kernel.org, Dave Young <dyoung@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        David Airlie <airlied@...ux.ie>, kexec@...ts.infradead.org,
        linux-doc@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH 13/15] mm: convert MAX_ORDER sized static arrays to dynamic ones.

On 5 Aug 2021, at 15:16, Christian König wrote:

> Am 05.08.21 um 21:02 schrieb Zi Yan:
>> From: Zi Yan <ziy@...dia.com>
>>
>> This prepares for the upcoming changes to make MAX_ORDER a boot time
>> parameter instead of compilation time constant. All static arrays with
>> MAX_ORDER size are converted to pointers and their memory is allocated
>> at runtime.
>
> Well in general I strongly suggest to not use the patter kmalloc(sizeof(some struct) * MAX_ORDER,...) instead use kmalloc_array, kcalloc etc..
>
> Then when a array is embedded at the end of a structure you can use a trailing array and the struct_size() macro to determine the allocation size.

Sure. Will fix it.

>
> Additional to that separating the patch into changes for TTM to make the maximum allocation order independent from MAX_ORDER would be rather good to have I think.

Can you elaborate a little bit more on “make the maximum allocation order independent from MAX_ORDER”? From what I understand of ttm_pool_alloc(), it tries to get num_pages pages by allocating as large pages as possible, starting from MAX_ORDER. What is the rationale behind this algorithm? Why not just call alloc_page(order=0) num_pages times? Is it mean to reduce the number of calls to alloc_page? The allocated pages do not need to get as high as MAX_ORDER, is that the case? If yes, I probably can keep ttm pool as static arrays with length of MIN_MAX_ORDER, which I introduce in Patch 14 as the lower bound of boot time parameter MAX_ORDER. Let me know your thoughts.

Thanks.

—
Best Regards,
Yan, Zi

Download attachment "signature.asc" of type "application/pgp-signature" (855 bytes)