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[2003:cb:c71a:2200:31c4:4d18:1bdd:fb7a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-35ef5d4729asm3794300f8f.25.2024.06.07.04.16.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 07 Jun 2024 04:16:04 -0700 (PDT) Message-ID: Date: Fri, 7 Jun 2024 13:16:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm: clear pte for folios that are zero filled To: Usama Arif , akpm@linux-foundation.org, shakeel.butt@linux.dev, yosryahmed@google.com, willy@infradead.org Cc: hannes@cmpxchg.org, 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> From: David Hildenbrand 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: 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: 8bit X-Rspamd-Queue-Id: 9740540025 X-Stat-Signature: a5ndwdoqyxpmcuri4baqkhhiy5bpko1u X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1717758968-880286 X-HE-Meta: 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 SEAe0joP 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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 07.06.24 12:24, Usama Arif wrote: > > On 04/06/2024 13:43, David Hildenbrand wrote: >> 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. >>> > Thanks for pointing this out David and Shakeel. This is a big issue in > this v2, and as Shakeel pointed out in [1] we need to do a second rmap > walk. Looking at how ksm deals with this in try_to_merge_one_page which > calls write_protect_page for each vma (i.e. basically an rmap walk), > this would be much more CPU expensive and complicated compared to v1 > [2], where the swap subsystem can handle all complexities. I will go > back to my v1 solution for the next revision as its much more simpler > and the memory usage is very low (0.003%) as pointed out by Johannes [3] > which would likely go away with the memory savings of not having a > zswap_entry for zero filled pages, and the solution being a lot simpler > than what a valid v2 approach would look like. Agreed. -- Cheers, David / dhildenb