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[2003:cb:c73a:3a00:a025:9b06:549e:c16b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4212f9b9ef1sm142213095e9.9.2024.06.04.05.43.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Jun 2024 05:43:51 -0700 (PDT) Message-ID: Date: Tue, 4 Jun 2024 14:43:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm: clear pte for folios that are zero filled From: David Hildenbrand To: Usama Arif , akpm@linux-foundation.org Cc: hannes@cmpxchg.org, willy@infradead.org, yosryahmed@google.com, nphamcs@gmail.com, chengming.zhou@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20240604105950.1134192-1-usamaarif642@gmail.com> <20240604105950.1134192-2-usamaarif642@gmail.com> <6b1485b6-c2a1-45b8-8afe-7b211689070b@redhat.com> Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <6b1485b6-c2a1-45b8-8afe-7b211689070b@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E4C4E18000C X-Stat-Signature: 6ffw8adbhuswofccnh5414ysb44f7wmt X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1717505037-236418 X-HE-Meta: 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 EV8aGjyV 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 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: List-Subscribe: List-Unsubscribe: On 04.06.24 14:30, David Hildenbrand wrote: > On 04.06.24 12:58, Usama Arif wrote: >> Approximately 10-20% of pages to be swapped out are zero pages [1]. >> Rather than reading/writing these pages to flash resulting >> in increased I/O and flash wear, the pte can be cleared for those >> addresses at unmap time while shrinking folio list. When this >> causes a page fault, do_pte_missing will take care of this page. >> With this patch, NVMe writes in Meta server fleet decreased >> by almost 10% with conventional swap setup (zswap disabled). >> >> [1] https://lore.kernel.org/all/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1/ >> >> Signed-off-by: Usama Arif >> --- >> include/linux/rmap.h | 1 + >> mm/rmap.c | 163 ++++++++++++++++++++++--------------------- >> mm/vmscan.c | 89 ++++++++++++++++------- >> 3 files changed, 150 insertions(+), 103 deletions(-) >> >> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >> index bb53e5920b88..b36db1e886e4 100644 >> --- a/include/linux/rmap.h >> +++ b/include/linux/rmap.h >> @@ -100,6 +100,7 @@ enum ttu_flags { >> * do a final flush if necessary */ >> TTU_RMAP_LOCKED = 0x80, /* do not grab rmap lock: >> * caller holds it */ >> + TTU_ZERO_FOLIO = 0x100,/* zero folio */ >> }; >> >> #ifdef CONFIG_MMU >> diff --git a/mm/rmap.c b/mm/rmap.c >> index 52357d79917c..d98f70876327 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1819,96 +1819,101 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> */ >> dec_mm_counter(mm, mm_counter(folio)); >> } else if (folio_test_anon(folio)) { >> - swp_entry_t entry = page_swap_entry(subpage); >> - pte_t swp_pte; >> - /* >> - * Store the swap location in the pte. >> - * See handle_pte_fault() ... >> - */ >> - if (unlikely(folio_test_swapbacked(folio) != >> - folio_test_swapcache(folio))) { >> + if (flags & TTU_ZERO_FOLIO) { >> + pte_clear(mm, address, pvmw.pte); >> + dec_mm_counter(mm, MM_ANONPAGES); > > Is there an easy way to reduce the code churn and highlight the added code? > > Like > > } else if (folio_test_anon(folio) && (flags & TTU_ZERO_FOLIO)) { > > } else if (folio_test_anon(folio)) { > > > > Also to concerns that I want to spell out: > > (a) what stops the page from getting modified in the meantime? The CPU > can write it until the TLB was flushed. > > (b) do you properly handle if the page is pinned (or just got pinned) > and we must not discard it? Oh, and I forgot, are you handling userfaultd as expected? IIRC there are some really nasty side-effects with userfaultfd even when userfaultfd is currently not registered for a VMA [1]. [1] https://lore.kernel.org/linux-mm/3a4b1027-df6e-31b8-b0de-ff202828228d@redhat.com/ What should work is replacing all-zero anonymous pages by the shared zeropage iff the anonymous page is not pinned and we synchronize against GUP fast. Well, and we handle possible concurrent writes accordingly. KSM does essentially that when told to de-duplicate the shared zeropage, and I was thinking a while ago if we would want a zeropage-only KSM version that doesn't need stable tress and all that, but only deduplicates zero-filled pages into the shared zeropage in a safe way. -- Cheers, David / dhildenb