linux-kernel - Re: [PATCH v3 0/4] mm: add more kernel parameters to control mTHP

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Message-ID: <f2a213eb-e69b-4572-b837-0c384bbb5960@igalia.com>
Date: Thu, 31 Oct 2024 08:04:58 -0300
From: Maíra Canal <mcanal@...lia.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, Hugh Dickins <hughd@...gle.com>,
 Barry Song <baohua@...nel.org>, David Hildenbrand <david@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Lance Yang
 <ioworker0@...il.com>, linux-mm@...ck.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel-dev@...lia.com
Subject: Re: [PATCH v3 0/4] mm: add more kernel parameters to control mTHP

Hi Andrew,

On 30/10/24 19:50, Andrew Morton wrote:
> On Wed, 30 Oct 2024 09:58:54 -0300 Maíra Canal <mcanal@...lia.com> wrote:
> 
>> The second and third patches focus on controlling THP support for shmem
>> via the kernel command line. The second patch introduces a parameter to
>> control the global default huge page allocation policy for the internal
>> shmem mount.
> 
> The changelogs for patches 2 and 3 both say
> 
> : By configuring ..., applications that use shmem, such as the DRM GEM objects,
> : can take advantage of mTHP before it's been configured through sysfs.
> 
> There isn't a lot of info here - please explain this timing issue in
> more detail.
> 
> Because the question which leaps to mind is: shouldn't the
> "applications that use shmem" be changed to "configure mTHP through
> sysfs" *before* "using shmem"?  Seems pretty basic.

Sorry about that, I'll try to improve the commit messages and add more 
details.

As mentioned in the example I gave ("DRM GEM objects"), my main use is
GEM objects backed by shmem. I'd like to use Huge Pages on the GPU and I
can only do that if I have contiguous memory to back my objects.

I can't think how I can change sysfs from a DRM driver.

Best Regards,
- Maíra

> 
> 
> Also, please consider my question to be a critique of the changelogs.
> If the changelogs were complete, I wouldn't need to ask any questions!