Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Content-Type: text/plain;
        charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.1\))
Subject: Re: [PATCH 01/13] mm: Update ptep_get_lockless()s comment
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <CAHk-=wj6EJvTtTeYQvkX3aOw6Q1SRYRV6xJP1+uHNvfAocO1hw@mail.gmail.com>
Date:   Sat, 29 Oct 2022 13:56:31 -0700
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jann Horn <jannh@google.com>, X86 ML <x86@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        jroedel@suse.de, ubizjak@gmail.com,
        Alistair Popple <apopple@nvidia.com>
Content-Transfer-Encoding: quoted-printable
Message-Id: <B39368D9-7E5D-4864-819C-CDEEAB4BD92D@gmail.com>
References: <20221022111403.531902164@infradead.org>
 <2c800ed1-d17a-def4-39e1-09281ee78d05@nvidia.com>
 <Y1ZGNwUEdm15W6Xz@hirez.programming.kicks-ass.net>
 <CAG48ez3fG=WnvbiE5mJaD66_gJj_hohnV8CqBG9eNdjd7pJW3A@mail.gmail.com>
 <Y1fsYwshJ93FT21r@hirez.programming.kicks-ass.net>
 <CAG48ez3VE+3dVdUMK+Pg_942gR+h_TCcSaFxGwCbNfh3W+mfOA@mail.gmail.com>
 <Y1f7YvKuwOl1XEwU@hirez.programming.kicks-ass.net>
 <CAG48ez05gBiB2w7bL_3O_OUoBWazmHnRwMiuni_wQyXBUcaxbQ@mail.gmail.com>
 <Y1oub9MvqwGBlHkq@hirez.programming.kicks-ass.net>
 <CAHk-=wihPdOtXgJ32pLB6Xd-UvnaZW9YvOOjM24JGYRjNHeykA@mail.gmail.com>
 <6C548A9A-3AF3-4EC1-B1E5-47A7FFBEB761@gmail.com>
 <CAHk-=wh8oi0qQtYDFTfm7d1s5C8mG7ig=NfzGWt4zbjXMzcdqQ@mail.gmail.com>
 <F9E42822-DA1D-4192-8410-3BAE42E9E4A9@gmail.com>
 <B88D3073-440A-41C7-95F4-895D3F657EF2@gmail.com>
 <CAHk-=wgzT1QsSCF-zN+eS06WGVTBg4sf=6oTMg95+AEq7QrSCQ@mail.gmail.com>
 <47678198-C502-47E1-B7C8-8A12352CDA95@gmail.com>
 <CAHk-=wjzngbbwHw4nAsqo_RpyOtUDk5G+Wus=O0w0A6goHvBWA@mail.gmail.com>
 <3a57cfc5-5db4-bdc9-1ddf-5305a37ffa62@nvidia.com>
 <CAHk-=wj6EJvTtTeYQvkX3aOw6Q1SRYRV6xJP1+uHNvfAocO1hw@mail.gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Precedence: bulk

On Oct 29, 2022, at 1:15 PM, Linus Torvalds =
<torvalds@linux-foundation.org> wrote:

> (b) we could move the "page_remove_rmap()" into the "flush-and-free" =
path too
>=20
> And (b) would be fairly easy - same model as that dirty bit patch,
> just a 'do page_remove_rmap too' - except page_remove_rmap() wants the
> vma as well (and we delay the TLB flush over multiple vma's, so it's
> not just a "save vma in mmu_gather=E2=80=9D).

(b) sounds reasonable and may potentially allow future performance
improvements (batching, doing stuff without locks).

It does appear to break a potential hidden assumption that rmap is =
removed
while the ptl is acquired (at least in the several instances I samples).
Yet, anyhow page_vma_mapped_walk() checks the PTE before calling the
function, so it should be fine.

I=E2=80=99ll give it a try.