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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH 2/2] mm: adds NOSIGBUS extension for out-of-band shmem read
Date:   Thu, 3 Jun 2021 12:24:56 -0700
Message-Id: <1FD047D2-F5F3-4AC6-A4E4-DB8FB1568821@amacapital.net>
References: <CAHk-=wiNT0RhwHkLa14ts0PGQtVtDZbJniOQJ66wxzXz4Co2mw@mail.gmail.com>
Cc:     Hugh Dickins <hughd@google.com>, Ming Lin <mlin@kernel.org>,
        Simon Ser <contact@emersion.fr>, 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>
In-Reply-To: <CAHk-=wiNT0RhwHkLa14ts0PGQtVtDZbJniOQJ66wxzXz4Co2mw@mail.gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Precedence: bulk


> On Jun 3, 2021, at 12:14 PM, Linus Torvalds <torvalds@linux-foundation.org=
> wrote:
>=20
> =EF=BB=BFOn Thu, Jun 3, 2021 at 12:07 PM Hugh Dickins <hughd@google.com> w=
rote:
>>=20
>> But the point that we've arrived at, that I'm actually now fairly
>> happy with, is do *not* permit MAP_NOSIGBUS on MAP_SHARED mappings.
>=20
> Yeah, if that's sufficient, then that original patch should just work as-i=
s.
>=20
> But there was some reason why people didn't like that patch
> originally, and I think it was literally about how it only worked on
> private mappings (the "we don't have a flag for it in the vm_flags"
> part was just a small detail.
>=20
> I guess that objection ended up changing over time.
>=20
>=20

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