linux-kernel - Re: [PATCH 3/5] drm/amdkfd: use vma_is_stack() and vma_is

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Date:   Fri, 14 Jul 2023 16:26:44 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Felix Kuehling <felix.kuehling@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-perf-users@...r.kernel.org,
        selinux@...r.kernel.org
Subject: Re: [PATCH 3/5] drm/amdkfd: use vma_is_stack() and vma_is_heap()

On 7/12/23 18:24, Felix Kuehling wrote:
> Allocations in the heap and stack tend to be small, with several 
> allocations sharing the same page. Sharing the same page for different 
> allocations with different access patterns leads to thrashing when we 
> migrate data back and forth on GPU and CPU access. To avoid this we 
> disable HMM migrations for head and stack VMAs.

Wonder how well does it really work in practice? AFAIK "heaps" (malloc())
today uses various arenas obtained by mmap() and not a single brk() managed
space anymore? And programs might be multithreaded, thus have multiple
stacks, while vma_is_stack() will recognize only the initial one...

Vlastimil

> Regards,
>    Felix
> 
> 
> Am 2023-07-12 um 10:42 schrieb Christoph Hellwig:
>> On Wed, Jul 12, 2023 at 10:38:29PM +0800, Kefeng Wang wrote:
>>> Use the helpers to simplify code.
>> Nothing against your addition of a helper, but a GPU driver really
>> should have no business even looking at this information..
>>
>>
>