linux-kernel - Re: [PATCH 2/2] mm: adds NOSIGBUS extension for out-of-band shmem read

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Message-ID: <ESvSq0tQ6RgG4pGNwnmAG4jf38xY8Uhg6hL-MBsU0nRE_rXmW_musHce9lnlWWKxkPMAnuH1Yg6o0V1lpO-RWlT7BktnvJEnQoYApKHIe48=@emersion.fr>
Date:   Thu, 03 Jun 2021 19:35:35 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, Ming Lin <mlin@...nel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm: adds NOSIGBUS extension for out-of-band shmem read

On Thursday, June 3rd, 2021 at 9:24 PM, Andy Lutomirski <luto@...capital.net> wrote:

> I don’t understand the use case well enough to comment on whether MAP_PRIVATE
> is sufficient, but I’m 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-r16GyfmWzqUzQ4KHbXJwEcjhzeoQ4sBTxx7QXDG9B6zk5AeT7FsNb3CSr94LaKy6Novh1fbbw8D_BBxYsbPLms=@emersion.fr/T/#mb321a8d39e824740877ba95f1df780ffd52c3862