linux-kernel - Re: [PATCH v4 2/5] drm/nouveau/uvmm: Allow larger pages

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Message-ID: <CAPv6GL3+Fs-7DCHGgk-rBpJjNHBLYvubbcBK-0U_Ew93_ka3Og@mail.gmail.com>
Date: Sat, 8 Nov 2025 20:30:09 +0100
From: Mary Guillemard <mary@...y.zone>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Mohamed Ahmed <mohamedahmedegypt2001@...il.com>, James Jones <jajones@...dia.com>, 
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	Faith Ekstrand <faith.ekstrand@...labora.com>, Lyude Paul <lyude@...hat.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	nouveau@...ts.freedesktop.org
Subject: Re: [PATCH v4 2/5] drm/nouveau/uvmm: Allow larger pages

Hi,

On Wed, Nov 5, 2025 at 11:50 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On 11/4/25 12:53 AM, Mohamed Ahmed wrote:
> > Thanks a lot for the shout out! Looking more at things, the logic here
> > is actually redundant. It was originally copied over directly from the
> > bo allocation code to stay on the safer side (basically the idea back
> > then was to make both the bo and vmm sides match exactly). We aren't
> > at risk of having an aligned address that is in the wrong memory type
> > because the bo allocation code (nouveau_bo.c:321) forces anything that
> > has the GART flag to have a page size of 4K. Anything getting a page
> > size higher than that is exclusively VRAM only. Additionally,
> > currently things marked VRAM only don't get evicted to host memory
> > except under high memory pressure and in that case, the context is
> > paused until the objects in question are paged back in, so we also
> > don't have to worry about memory placement there.
> >
> > The memory placement check in the vmm code could be removed but I am
> > leaning more towards leaving it as is just to stay on the safer side.
>
> If it is not necessary, please remove it. We should not carry dead code.
>

For correctness, this code path needs to refuse incompatible domains
to decide the appropriate page size.
As such those checks should remain.

Regards,
Mary