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From:   Zi Yan <ziy@nvidia.com>
To:     Christian =?utf-8?q?K=C3=B6nig?= <christian.koenig@amd.com>
Cc:     David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Michal Hocko <mhocko@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        linux-kernel@vger.kernel.org, Dave Young <dyoung@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        David Airlie <airlied@linux.ie>, kexec@lists.infradead.org,
        linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [RFC PATCH 13/15] mm: convert MAX_ORDER sized static arrays to dynamic ones.
Date:   Thu, 05 Aug 2021 15:58:32 -0400
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On 5 Aug 2021, at 15:16, Christian K=C3=B6nig wrote:

> Am 05.08.21 um 21:02 schrieb Zi Yan:
>> From: Zi Yan <ziy@nvidia.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 t=
railing array and the struct_size() macro to determine the allocation siz=
e.

Sure. Will fix it.

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

Can you elaborate a little bit more on =E2=80=9Cmake the maximum allocati=
on order independent from MAX_ORDER=E2=80=9D? From what I understand of t=
tm_pool_alloc(), it tries to get num_pages pages by allocating as large p=
ages as possible, starting from MAX_ORDER. What is the rationale behind t=
his algorithm? Why not just call alloc_page(order=3D0) num_pages times? I=
s it mean to reduce the number of calls to alloc_page? The allocated page=
s do not need to get as high as MAX_ORDER, is that the case? If yes, I pr=
obably can keep ttm pool as static arrays with length of MIN_MAX_ORDER, w=
hich I introduce in Patch 14 as the lower bound of boot time parameter MA=
X_ORDER. Let me know your thoughts.

Thanks.

=E2=80=94
Best Regards,
Yan, Zi

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