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[2003:cb:c735:1900:ac8b:7ae5:991f:54fc]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390cd86cb08sm150988f8f.29.2025.02.24.13.17.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Feb 2025 13:17:48 -0800 (PST) Message-ID: Date: Mon, 24 Feb 2025 22:17:46 +0100 Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 19/20] fs/proc/task_mmu: remove per-page mapcount dependency for smaps/smaps_rollup (CONFIG_NO_PAGE_MAPCOUNT) To: Zi Yan , linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, Andrew Morton , "Matthew Wilcox (Oracle)" , Tejun Heo , Zefan Li , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn References: <20250224165603.1434404-1-david@redhat.com> <20250224165603.1434404-20-david@redhat.com> From: David Hildenbrand Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 24.02.25 21:53, Zi Yan wrote: > On Mon Feb 24, 2025 at 11:56 AM EST, David Hildenbrand wrote: >> Let's implement an alternative when per-page mapcounts in large folios are >> no longer maintained -- soon with CONFIG_NO_PAGE_MAPCOUNT. >> >> When computing the output for smaps / smaps_rollups, in particular when >> calculating the USS (Unique Set Size) and the PSS (Proportional Set Size), >> we still rely on per-page mapcounts. >> >> To determine private vs. shared, we'll use folio_likely_mapped_shared(), >> similar to how we handle PM_MMAP_EXCLUSIVE. Similarly, we might now >> under-estimate the USS and count pages towards "shared" that are >> actually "private" ("exclusively mapped"). >> >> When calculating the PSS, we'll now also use the average per-page >> mapcount for large folios: this can result in both, an over-estimation >> and an under-estimation of the PSS. The difference is not expected to >> matter much in practice, but we'll have to learn as we go. >> >> We can now provide folio_precise_page_mapcount() only with >> CONFIG_PAGE_MAPCOUNT, and remove one of the last users of per-page >> mapcounts when CONFIG_NO_PAGE_MAPCOUNT is enabled. >> >> Document the new behavior. >> >> Signed-off-by: David Hildenbrand >> --- >> Documentation/filesystems/proc.rst | 13 +++++++++++++ >> fs/proc/internal.h | 8 ++++++++ >> fs/proc/task_mmu.c | 17 +++++++++++++++-- >> 3 files changed, 36 insertions(+), 2 deletions(-) >> >> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst >> index 1aa190017f796..57d55274a1f42 100644 >> --- a/Documentation/filesystems/proc.rst >> +++ b/Documentation/filesystems/proc.rst >> @@ -506,6 +506,19 @@ Note that even a page which is part of a MAP_SHARED mapping, but has only >> a single pte mapped, i.e. is currently used by only one process, is accounted >> as private and not as shared. >> >> +Note that in some kernel configurations, all pages part of a larger allocation >> +(e.g., THP) might be considered "shared" if the large allocation is >> +considered "shared": if not all pages are exclusive to the same process. >> +Further, some kernel configurations might consider larger allocations "shared", >> +if they were at one point considered "shared", even if they would now be >> +considered "exclusive". >> + >> +Some kernel configurations do not track the precise number of times a page part >> +of a larger allocation is mapped. In this case, when calculating the PSS, the >> +average number of mappings per page in this larger allocation might be used >> +as an approximation for the number of mappings of a page. The PSS calculation >> +will be imprecise in this case. >> + >> "Referenced" indicates the amount of memory currently marked as referenced or >> accessed. >> >> diff --git a/fs/proc/internal.h b/fs/proc/internal.h >> index 16aa1fd260771..70205425a2daa 100644 >> --- a/fs/proc/internal.h >> +++ b/fs/proc/internal.h >> @@ -143,6 +143,7 @@ unsigned name_to_int(const struct qstr *qstr); >> /* Worst case buffer size needed for holding an integer. */ >> #define PROC_NUMBUF 13 >> >> +#ifdef CONFIG_PAGE_MAPCOUNT >> /** >> * folio_precise_page_mapcount() - Number of mappings of this folio page. >> * @folio: The folio. >> @@ -173,6 +174,13 @@ static inline int folio_precise_page_mapcount(struct folio *folio, >> >> return mapcount; >> } >> +#else /* !CONFIG_PAGE_MAPCOUNT */ >> +static inline int folio_precise_page_mapcount(struct folio *folio, >> + struct page *page) >> +{ >> + BUILD_BUG(); >> +} >> +#endif /* CONFIG_PAGE_MAPCOUNT */ >> >> /** >> * folio_average_page_mapcount() - Average number of mappings per page in this >> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c >> index d7ee842367f0f..7ca0bc3bf417d 100644 >> --- a/fs/proc/task_mmu.c >> +++ b/fs/proc/task_mmu.c >> @@ -707,6 +707,8 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page, >> struct folio *folio = page_folio(page); >> int i, nr = compound ? compound_nr(page) : 1; >> unsigned long size = nr * PAGE_SIZE; >> + bool exclusive; >> + int mapcount; >> >> /* >> * First accumulate quantities that depend only on |size| and the type >> @@ -747,18 +749,29 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page, >> dirty, locked, present); >> return; >> } >> + >> + if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) { >> + mapcount = folio_average_page_mapcount(folio); > > This seems inconsistent with how folio_average_page_mapcount() is used > in patch 16 and 18. It only looks that way. Note that the code below only does >> if (mapcount >= 2) >> pss /= mapcount; Having it as 0 or 1 doesn't matter in that regard. Thanks! -- Cheers, David / dhildenb