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(p200300cbc7092700cdd8dcb02a698783.dip0.t-ipconnect.de. [2003:cb:c709:2700:cdd8:dcb0:2a69:8783]) by smtp.gmail.com with ESMTPSA id w8sm20054277wre.83.2022.01.26.06.36.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Jan 2022 06:36:43 -0800 (PST) Message-ID: <683d7a13-70a5-6ba9-e290-9ac4db309535@redhat.com> Date: Wed, 26 Jan 2022 15:36:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH RFC v2 2/9] mm: optimize do_wp_page() for fresh pages in local LRU pagevecs To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Vlastimil Babka , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , linux-mm@kvack.org References: <20220126095557.32392-1-david@redhat.com> <20220126095557.32392-3-david@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 60392140018 X-Rspam-User: nil Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Isz0DZJh; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf09.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com X-Stat-Signature: t16m49md7mc1nru9i9ibwj4xd385acwt X-Rspamd-Server: rspam08 X-HE-Tag: 1643207813-181421 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 26.01.22 15:31, Matthew Wilcox wrote: > On Wed, Jan 26, 2022 at 10:55:50AM +0100, David Hildenbrand wrote: >> diff --git a/mm/memory.c b/mm/memory.c >> index bcd3b7c50891..61d67ceef734 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -3298,7 +3298,17 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) >> * >> * PageKsm() doesn't necessarily raise the page refcount. >> */ >> - if (PageKsm(page) || page_count(page) > 1 + PageSwapCache(page)) >> + if (PageKsm(page)) >> + goto copy; >> + if (page_count(page) > 1 + PageSwapCache(page) + !PageLRU(page)) >> + goto copy; >> + if (!PageLRU(page)) >> + /* >> + * Note: We cannot easily detect+handle references from >> + * remote LRU pagevecs or references to PageLRU() pages. >> + */ >> + lru_add_drain(); >> + if (page_count(page) > 1 + PageSwapCache(page)) >> goto copy; > > I worry we're starting to get too accurate here. How about: > In that simplified case we'll essentially trylock_page() and for most pages that are ordinarily shared by e.g., 2 processes. > if (PageKsm(page) || page_count(page) > 3) > goto copy; > if (!PageLRU(page)) > lru_add_drain(); > if (!trylock_page(page)) > goto copy; > ... > I think we might at least want the if (page_count(page) > 1 + PageSwapCache(page)) goto copy; check here. >> if (!trylock_page(page)) >> goto copy; >> -- >> 2.34.1 >> > -- Thanks, David / dhildenb