linux-kernel - Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages

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Date:   Tue, 23 Mar 2021 16:59:49 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Thomas Hellstr??m (Intel)" <thomas_os@...pmail.org>,
        dri-devel@...ts.freedesktop.org,
        Christian Koenig <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] mm,drm/ttm: Block fast GUP to TTM huge pages

On Tue, Mar 23, 2021 at 01:37:15PM -0300, Jason Gunthorpe wrote:
> Isn't the devmap PTE flag arch optional? Does this fall back to not
> using huge pages on arches that don't support it?
> 
> Also, I feel like this code to install "pte_special" huge pages does
> not belong in the drm subsystem..

It doesn't.  Unfortunately the drm code has a lot of such warts where
it pokes way to deep into VM internals.