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[2003:cb:c74b:bf00:182c:d606:87cf:6fea]) by smtp.gmail.com with ESMTPSA id l27-20020a05600c1d1b00b0041c5151dc1csm20990620wms.29.2024.05.06.13.53.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 May 2024 13:53:29 -0700 (PDT) Message-ID: Date: Mon, 6 May 2024 22:53:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: do not update memcg stats for NR_{FILE/SHMEM}_PMDMAPPED To: Yosry Ahmed Cc: Andrew Morton , Shakeel Butt , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+9319a4268a640e26b72b@syzkaller.appspotmail.com References: <20240506192924.271999-1-yosryahmed@google.com> <42b09dc5-cfb1-4bd7-b5e3-8b631498d08f@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; 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Commit >>>>> 14e0f6c957e39 ("memcg: reduce memory for the lruvec and memcg stats") >>>>> changed this such that we only maintain the stats we actually expose >>>>> per-memcg via a translation table. >>>>> >>>>> Additionally, commit 514462bbe927b ("memcg: warn for unexpected events >>>>> and stats") added a warning if a per-memcg stat update is attempted for >>>>> a stat that is not in the translation table. The warning started firing >>>>> for the NR_{FILE/SHMEM}_PMDMAPPED stat updates in the rmap code. These >>>>> stats are not maintained per-memcg, and hence are not in the translation >>>>> table. >>>>> >>>>> Do not use __lruvec_stat_mod_folio() when updating NR_FILE_PMDMAPPED and >>>>> NR_SHMEM_PMDMAPPED. Use __mod_node_page_state() instead, which updates >>>>> the global per-node stats only. >>>>> >>>>> Reported-by: syzbot+9319a4268a640e26b72b@syzkaller.appspotmail.com >>>>> Closes: https://lore.kernel.org/lkml/0000000000001b9d500617c8b23c@google.com >>>>> Fixes: 514462bbe927 ("memcg: warn for unexpected events and stats") >>>>> Acked-by: Shakeel Butt >>>>> Signed-off-by: Yosry Ahmed >>>>> --- >>>>> mm/rmap.c | 15 +++++++++------ >>>>> 1 file changed, 9 insertions(+), 6 deletions(-) >>>>> >>>>> diff --git a/mm/rmap.c b/mm/rmap.c >>>>> index 12be4241474ab..ed7f820369864 100644 >>>>> --- a/mm/rmap.c >>>>> +++ b/mm/rmap.c >>>>> @@ -1435,13 +1435,14 @@ static __always_inline void __folio_add_file_rmap(struct folio *folio, >>>>> struct page *page, int nr_pages, struct vm_area_struct *vma, >>>>> enum rmap_level level) >>>>> { >>>>> + pg_data_t *pgdat = folio_pgdat(folio); >>>>> int nr, nr_pmdmapped = 0; >>>>> VM_WARN_ON_FOLIO(folio_test_anon(folio), folio); >>>>> nr = __folio_add_rmap(folio, page, nr_pages, level, &nr_pmdmapped); >>>>> if (nr_pmdmapped) >>>>> - __lruvec_stat_mod_folio(folio, folio_test_swapbacked(folio) ? >>>>> + __mod_node_page_state(pgdat, folio_test_swapbacked(folio) ? >>>>> NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped); >>>>> if (nr) >>>>> __lruvec_stat_mod_folio(folio, NR_FILE_MAPPED, nr); >>>>> @@ -1493,6 +1494,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio, >>>>> enum rmap_level level) >>>>> { >>>>> atomic_t *mapped = &folio->_nr_pages_mapped; >>>>> + pg_data_t *pgdat = folio_pgdat(folio); >>>>> int last, nr = 0, nr_pmdmapped = 0; >>>>> bool partially_mapped = false; >>>>> enum node_stat_item idx; >>>>> @@ -1540,13 +1542,14 @@ static __always_inline void __folio_remove_rmap(struct folio *folio, >>>>> } >>>>> if (nr_pmdmapped) { >>>>> + /* NR_{FILE/SHMEM}_PMDMAPPED are not maintained per-memcg */ >>>>> if (folio_test_anon(folio)) >>>>> - idx = NR_ANON_THPS; >>>>> - else if (folio_test_swapbacked(folio)) >>>>> - idx = NR_SHMEM_PMDMAPPED; >>>>> + __lruvec_stat_mod_folio(folio, NR_ANON_THPS, -nr_pmdmapped); >>>>> else >>>>> - idx = NR_FILE_PMDMAPPED; >>>>> - __lruvec_stat_mod_folio(folio, idx, -nr_pmdmapped); >>>>> + __mod_node_page_state(pgdat, >>>> >>>> folio_pgdat(folio) should fit here easily. :) >>>> >>>> But I would actually suggest something like the following in mm/rmap.c >>> >>> I am not a big fan of this. Not because I don't like the abstraction, >>> but because I think it doesn't go all the way. It abstracts a very >>> certain case: updating nr_pmdmapped for file folios. >>> >> >> Right. It only removes some of the ugliness ;) > > I think if we do this we just add one unnecessary layer of indirection > to one case. If anything people will wonder why we have a helper only > for this case. Just my 2c :) > >> >>> I think if we opt for abstracting the stats updates in mm/rmap.c, we >>> should go all the way with something like the following (probably split >>> as two patches: refactoring then bug fix). WDYT about the below? >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index 12be4241474ab..70d6f6309da01 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1269,6 +1269,28 @@ static void __page_check_anon_rmap(struct folio *folio, struct page *page, >>> page); >>> } >>> >>> +static void __foio_mod_stat(struct folio *folio, int nr, int nr_pmdmapped) >>> +{ >>> + int idx; >>> + >>> + if (nr) { >>> + idx = folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED; >>> + __lruvec_stat_mod_folio(folio, idx, nr); >>> + } >>> + if (nr_pmdmapped) { >>> + if (folio_test_anon(folio)) { >>> + idx = NR_ANON_THPS; >>> + __lruvec_stat_mod_folio(folio, idx, nr_pmdmapped); >>> + } else { >>> + /* NR_*_PMDMAPPED are not maintained per-memcg */ >>> + idx = folio_test_swapbacked(folio) ? >>> + NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED; >>> + __mod_node_page_state(folio_pgdat(folio), idx, >>> + nr_pmdmapped); >>> + } >>> + } >>> +} >>> + >> >> I didn't suggest that, because in the _anon and _file functions we'll >> end up introducing unnecessary folio_test_anon() checks that the >> compiler cannot optimize out. > > I convinced myself that the folio_test_anon() will be #free because > the struct folio should be already in the cache at this point, of > course I may be delusional :) Well, nothing is free :) But yes, likely it won't matter much. > > We can pass in an @anon boolean parameter, but it becomes an ugliness > tradeoff at this point :) Agreed. > > Anyway, I don't feel strongly either way. I am fine with keeping the > patch as-is, the diff I proposed above, or the diff I proposed with an > @anon parameter of folio_test_anon(). The only option I don't really > like is adding a helper just for the file pmdmapped case. Let's go with your cleanup here (could do as separate cleanup on top of v2, whatever you prefer). -- Cheers, David / dhildenb