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Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn References: <20250224165603.1434404-1-david@redhat.com> <20250224165603.1434404-18-david@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: <20250224165603.1434404-18-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 64bsfhmYFdQwRdxywl-P_krkyC6fEQI8czVbHGBFVFY_1740481014 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: D2284180008 X-Stat-Signature: 3offe45mdk3kjzyo3xrczukrxua5ycwx X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1740481016-427693 X-HE-Meta: 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 +R78XXae 2X+4DWY9aRtGX3Gg5kanwe+EXHakHJtQj88clkrDErMXwOyns6FmVJ+mlbOukUUKPjLwxCN9IO//Y/iTrWXOpLiTvKOSNa9Kg9+2y+eYRG1Twq+rAHNW/1aSHppCTsnzjBOhKfZ0vAgJqma/lbDGmq/H2GbJQJS61fjPWcSTerLg3vmpLacPe1SodJQ5V/npz9bMdbFqfC2GZ1Vow0C2y9gmFDhFlFlw9V88uw/UOY5zj+WzEpfcpuX0y8Uy3RvN29qUbShCyraA/ZcKNQvubhzfFH+di52ut75XoHswShonpjteTMU9Dl6s/hH5ffHo5CHwcPB+EiR+ey0XRKGmBu46Q6wnThoVZxu7LXOdxoLF/6U7UdPvKwOcC+3vxnFIO0BgGqUscncZXsljPMdYeKExafD8ktLh4uMRIgmFOlQgrEkJtXedlLB79/XBPJWef9zZxwgkNaFxWvsf5fXpPxF4utg== 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 24.02.25 17:55, 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. > > PM_MMAP_EXCLUSIVE will now be set if folio_likely_mapped_shared() is > true -- when the folio is considered "mapped shared", including when > it once was "mapped shared" but no longer is, as documented. > > This might result in and under-indication of "exclusively mapped", which > is considered better than over-indicating it: under-estimating the USS > (Unique Set Size) is better than over-estimating it. > > As an alternative, we could simply remove that flag with > CONFIG_NO_PAGE_MAPCOUNT completely, but there might be value to it. So, > let's keep it like that and document the behavior. > > Signed-off-by: David Hildenbrand > --- > Documentation/admin-guide/mm/pagemap.rst | 9 +++++++++ > fs/proc/task_mmu.c | 11 +++++++++-- > 2 files changed, 18 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst > index 49590306c61a0..131c86574c39a 100644 > --- a/Documentation/admin-guide/mm/pagemap.rst > +++ b/Documentation/admin-guide/mm/pagemap.rst > @@ -37,6 +37,15 @@ There are four components to pagemap: > precisely which pages are mapped (or in swap) and comparing mapped > pages between processes. > > + Note that in some kernel configurations, all pages part of a larger > + allocation (e.g., THP) might be considered "mapped shared" if the large > + allocation is considered "mapped shared": if not all pages are exclusive to > + the same process. Further, some kernel configurations might consider larger > + allocations "mapped shared", if they were at one point considered > + "mapped shared", even if they would now be considered "exclusively mapped". > + Consequently, in these kernel configurations, bit 56 might be set although > + the page is actually "exclusively mapped" I rewrote this yet another time to maybe make it clearer ... + Traditionally, bit 56 indicates that a page is mapped exactly once and bit + 56 is clear when a page is mapped multiple times, even when mapped in the + same process multiple times. In some kernel configurations, the semantics + for pages part of a larger allocation (e.g., THP) differ: bit 56 is set if + all pages part of the corresponding large allocation are *certainly* mapped + in the same process, even if the page is mapped multiple times in that + process. Bit 56 is clear when any page page of the larger allocation + is *maybe* mapped in a different process. In some cases, a large allocation + might be treated as "maybe mapped by multiple processes" even though this + is no longer the case. (talking about "process" is not completely correct, it's actually "MMs"; but that might add more confusion here) -- Cheers, David / dhildenb