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Tue, 22 Sep 2020 18:44:09 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.146]) by smtp.corp.redhat.com (Postfix) with SMTP id CC09B1A800; Tue, 22 Sep 2020 18:44:01 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 22 Sep 2020 20:44:08 +0200 (CEST) Date: Tue, 22 Sep 2020 20:44:00 +0200 From: Oleg Nesterov To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linus Torvalds , Michal Hocko , Kirill Shutemov , Jann Horn , Kirill Tkhai , Hugh Dickins , Leon Romanovsky , Jan Kara , John Hubbard , Christoph Hellwig , Andrew Morton , Jason Gunthorpe , Andrea Arcangeli Subject: Re: [PATCH 4/5] mm: Do early cow for pinned pages during fork() for ptes Message-ID: <20200922184359.GI11679@redhat.com> References: <20200921211744.24758-1-peterx@redhat.com> <20200921212028.25184-1-peterx@redhat.com> <20200922114839.GC11679@redhat.com> <20200922124013.GD11679@redhat.com> <20200922155842.GG19098@xz-x1> <20200922165216.GF11679@redhat.com> <20200922183438.GL19098@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200922183438.GL19098@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09/22, Peter Xu wrote: > > Or I can also do it in inverted order if you think better: > > if (unlikely(copy_ret == COPY_MM_BREAK_COW)) { > WARN_ON_ONCE(!data.cow_new_page); > ... > } Peter, let me say this again. I don't understand this code enough, you can safely ignore me ;) However. Personally I strongly prefer the above. Personally I really dislike this part of 4/5: again: + /* We don't reset this for COPY_MM_BREAK_COW */ + memset(&data, 0, sizeof(data)); + +again_break_cow: If we rely on "copy_ret == COPY_MM_BREAK_COW" we can unify "again" and "again_break_cow", we don't need to clear ->cow_new_page, this makes the logic more understandable. To me at least ;) Oleg.