linux-kernel - Re: [PATCH 4/4] mm: delay page_remove_rmap() until after the TLB has been flushed

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Message-Id: <519E803D-4D58-4252-B596-A40D7C156BC1@gmail.com>
Date:   Tue, 8 Nov 2022 13:05:39 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Will Deacon <will@...nel.org>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
        Nick Piggin <npiggin@...il.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 4/4] mm: delay page_remove_rmap() until after the TLB has
 been flushed

On Nov 8, 2022, at 11:41 AM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> When we remove a page table entry, we are very careful to only free the
> page after we have flushed the TLB, because other CPUs could still be
> using the page through stale TLB entries until after the flush.

The patches (all 4) look fine to me.

I mean there are minor issues here and there, like s390’s tlb_flush_rmaps()
that can have VM_WARN_ON(1);the generic tlb_flush_rmaps() that is missing an
empty line after the ‘page' variable definition; or perhaps using __bitwise
for sparse (as David pointed) — but it can all be addressed later.