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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id m11-20020a05620a290b00b006e702033b15sm1275350qkp.66.2022.12.09.06.39.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Dec 2022 06:39:32 -0800 (PST) Date: Fri, 9 Dec 2022 09:39:30 -0500 From: Peter Xu To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song , John Hubbard , Andrea Arcangeli , James Houghton , Jann Horn , Rik van Riel , Miaohe Lin , Andrew Morton , Mike Kravetz , Nadav Amit Subject: Re: [PATCH v2 08/10] mm/hugetlb: Make walk_hugetlb_range() safe to pmd unshare Message-ID: References: <20221207203034.650899-1-peterx@redhat.com> <20221207203034.650899-9-peterx@redhat.com> <72a62bf5-7633-f35f-75fd-0222fd0ab49f@redhat.com> MIME-Version: 1.0 In-Reply-To: <72a62bf5-7633-f35f-75fd-0222fd0ab49f@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D6EEC140004 X-Rspam-User: X-Stat-Signature: gpx3do5hnahr6ddzfmtepgz7y366ycss X-HE-Tag: 1670596776-757725 X-HE-Meta: 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 xlmwa1jh GtU3BK869Vln9+ambo1uyZ1iUU4kjKYOzbeFsH6HKU29ZGqHeIckFBHV3lvCiyWupNKmCjt0oGJDq/JlEFcfvv2booFYl6N/j1/GyPU2TwuAG0c6j8hIJaiLHSMxbd6EvWYykUO4OpRnjf5k7dGfnBHorwOtBZlqpIBv1O46LZU1qa972sGimp/2Rg7ZS7fe6S9BwT8z/QDzlLAw7HCKZ74GmXp5nXjDVTbUg 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 Fri, Dec 09, 2022 at 11:24:55AM +0100, David Hildenbrand wrote: > For such cases, it would be good to have any evidence that it really helps. I don't know much on the s390 path, but if a process has a large hugetlb vma, even MADV_DONTNEED will be blocked for whatever long time if there's another process or thread scanning pagemap for this vma. Would this justify a bit? It's just that the vma lock is taken write far more than mmap_lock taken write I think, meanwhile what we need here is only release the lock and retake, nothing else. It didn't make things over complicated, IMO. No strong ipinion from my side, as I said to me it's really low hanging fruit. If you still think that doesn't justify and if Mike doesn't have a preference either I can just drop it for later. -- Peter Xu