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Date:   Thu, 03 Jun 2021 19:35:35 +0000
To:     Andy Lutomirski <luto@amacapital.net>
From:   Simon Ser <contact@emersion.fr>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>, Ming Lin <mlin@kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
Reply-To: Simon Ser <contact@emersion.fr>
Subject: Re: [PATCH 2/2] mm: adds NOSIGBUS extension for out-of-band shmem read
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On Thursday, June 3rd, 2021 at 9:24 PM, Andy Lutomirski <luto@amacapital.ne=
t> wrote:

> I don=E2=80=99t understand the use case well enough to comment on whether=
 MAP_PRIVATE
> is sufficient, but I=E2=80=99m with Hugh: if this feature is implemented =
for
> MAP_SHARED, it should be fully coherent.

I've tried to explain what we'd need from user-space PoV in [1].
tl;dr the MAP_PRIVATE restriction would get us pretty far, even if it
won't allow us to have all of the bells and whistles.

[1]: https://lore.kernel.org/linux-mm/vs1Us2sm4qmfvLOqNat0-r16GyfmWzqUzQ4KH=
bXJwEcjhzeoQ4sBTxx7QXDG9B6zk5AeT7FsNb3CSr94LaKy6Novh1fbbw8D_BBxYsbPLms=3D@e=
mersion.fr/T/#mb321a8d39e824740877ba95f1df780ffd52c3862