linux-kernel - Re: [RFC PATCH] mm: Fetch the dirty bit before we reset the pte

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Date:   Thu, 8 Oct 2020 10:30:30 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Leon Romanovsky <leonro@...dia.com>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nick Piggin <npiggin@...il.com>, Peter Xu <peterx@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Michal Hocko <mhocko@...e.com>,
        Kirill Shutemov <kirill@...temov.name>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC PATCH] mm: Fetch the dirty bit before we reset the pte

On Thu, Oct 8, 2020 at 10:02 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Here's the first patch anyway. If you actually have a test-case where
> this matters, I guess I need to apply it now..

Actually, I removed the "__page_mapcount()" part of that patch, to
keep it minimal and _only_ do remove the wrprotect trick.

We can do the __page_mapcount() optimization and the mm sequence count
for 5.10 (although so far nobody has actually written the seqcount
patch - I think it would be a trivial few-liner, but I guess it won't
make 5.10 at this point).

So here's what I ended up with.

                      Linus

View attachment "0001-mm-avoid-early-COW-write-protect-games-during-fork.patch" of type "text/x-patch" (5138 bytes)