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[2003:d8:2f4f:2b00:69b5:3684:56c:6dd5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-422870e9676sm88408935e9.24.2024.06.14.02.04.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Jun 2024 02:04:19 -0700 (PDT) Message-ID: Date: Fri, 14 Jun 2024 11:04:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 3/3] mm: remove folio_test_anon(folio)==false path in __folio_add_anon_rmap() To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, chrisl@kernel.org, linux-kernel@vger.kernel.org, mhocko@suse.com, ryan.roberts@arm.com, baolin.wang@linux.alibaba.com, yosryahmed@google.com, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, ying.huang@intel.com, yuzhao@google.com References: <20240613000721.23093-1-21cnbao@gmail.com> <20240613000721.23093-4-21cnbao@gmail.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-Server: rspam07 X-Rspamd-Queue-Id: 121A9180007 X-Stat-Signature: a5ot1cew7mwt5dwcozkb4qjmxwb339he X-Rspam-User: X-HE-Tag: 1718355863-388926 X-HE-Meta: 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 4CGL/vpy 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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 14.06.24 10:58, Barry Song wrote: > On Fri, Jun 14, 2024 at 8:56 PM Barry Song <21cnbao@gmail.com> wrote: >> >> On Fri, Jun 14, 2024 at 8:51 PM David Hildenbrand wrote: >>> >>> On 14.06.24 09:56, Barry Song wrote: >>>> On Thu, Jun 13, 2024 at 9:12 PM David Hildenbrand wrote: >>>>> >>>>> On 13.06.24 11:06, Barry Song wrote: >>>>>> On Thu, Jun 13, 2024 at 8:49 PM David Hildenbrand wrote: >>>>>>> >>>>>>> On 13.06.24 10:46, Barry Song wrote: >>>>>>>> On Thu, Jun 13, 2024 at 12:08 PM Barry Song <21cnbao@gmail.com> wrote: >>>>>>>>> >>>>>>>>> From: Barry Song >>>>>>>>> >>>>>>>>> The folio_test_anon(folio)==false case within do_swap_page() has been >>>>>>>>> relocated to folio_add_new_anon_rmap(). Additionally, two other callers >>>>>>>>> consistently pass anonymous folios. >>>>>>>>> >>>>>>>>> stack 1: >>>>>>>>> remove_migration_pmd >>>>>>>>> -> folio_add_anon_rmap_pmd >>>>>>>>> -> __folio_add_anon_rmap >>>>>>>>> >>>>>>>>> stack 2: >>>>>>>>> __split_huge_pmd_locked >>>>>>>>> -> folio_add_anon_rmap_ptes >>>>>>>>> -> __folio_add_anon_rmap >>>>>>>>> >>>>>>>>> __folio_add_anon_rmap() only needs to handle the cases >>>>>>>>> folio_test_anon(folio)==true now. >>>>>>>> >>>>>>>> My team reported a case where swapoff() is calling >>>>>>>> folio_add_anon_rmap_pte *not* folio_add_anon_rmap_ptes >>>>>>>> with one new anon (!folio_test_anon(folio)). >>>>>>>> >>>>>>>> I will double check all folio_add_anon_rmap_pte() cases. >>>>>>> >>>>>>> Right, swapoff() path is a bit special (e.g., we don't do any kind of >>>>>>> batching on the swapoff() path). >>>>>>> >>>>>>> But we should never get a new large anon folio there, or could that now >>>>>>> happen? >>>>>> >>>>>> My team encountered the following issue while testing this RFC >>>>>> series on real hardware. Let me take a look to identify the >>>>>> problem. >>>>>> >>>>>> [ 261.214195][T11285] page:000000004cdd779e refcount:4 mapcount:1 >>>>>> mapping:00000000ba142c22 index:0x1 pfn:0x1b30a6 >>>>>> [ 261.214213][T11285] memcg:ffffff8003678000 >>>>>> [ 261.214217][T11285] aops:swap_aops >>>>>> [ 261.214233][T11285] flags: >>>>>> 0x2000000000081009(locked|uptodate|owner_priv_1|swapbacked|zone=1|kasantag=0x0) >>>>>> [ 261.214241][T11285] page_type: 0x0() >>>>>> [ 261.214246][T11285] raw: 2000000000081009 0000000000000000 >>>>>> dead000000000122 0000000000000000 >>>>>> [ 261.214251][T11285] raw: 0000000000000001 00000000000d84b3 >>>>>> 0000000400000000 ffffff8003678000 >>>>>> [ 261.214254][T11285] page dumped because: >>>>>> VM_WARN_ON_FOLIO(!folio_test_anon(folio)) >>>>>> [ 261.214257][T11285] page_owner tracks the page as allocated >>>>>> [ 261.214260][T11285] page last allocated via order 0, migratetype >>>>>> Movable, gfp_mask 0x2140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid >>>>>> 11285, tgid 11285 (swapoff), ts 261214177545, free_ts 261151875699 >>>>>> [ 261.214268][T11285] post_alloc_hook+0x1b8/0x1c0 >>>>>> [ 261.214284][T11285] prep_new_page+0x28/0x13c >>>>>> [ 261.214291][T11285] get_page_from_freelist+0x198c/0x1aa4 >>>>>> [ 261.214298][T11285] __alloc_pages+0x15c/0x330 >>>>>> [ 261.214304][T11285] __folio_alloc+0x1c/0x4c >>>>>> [ 261.214310][T11285] __read_swap_cache_async+0xd8/0x48c >>>>>> [ 261.214320][T11285] swap_cluster_readahead+0x158/0x324 >>>>>> [ 261.214326][T11285] swapin_readahead+0x64/0x448 >>>>>> [ 261.214331][T11285] __arm64_sys_swapoff+0x6ec/0x14b0 >>>>>> [ 261.214337][T11285] invoke_syscall+0x58/0x114 >>>>>> [ 261.214353][T11285] el0_svc_common+0xac/0xe0 >>>>>> [ 261.214360][T11285] do_el0_svc+0x1c/0x28 >>>>>> [ 261.214366][T11285] el0_svc+0x38/0x68 >>>>>> [ 261.214372][T11285] el0t_64_sync_handler+0x68/0xbc >>>>>> [ 261.214376][T11285] el0t_64_sync+0x1a8/0x1ac >>>>>> [ 261.214381][T11285] page last free pid 90 tgid 90 stack trace: >>>>>> [ 261.214386][T11285] free_unref_page_prepare+0x338/0x374 >>>>>> [ 261.214395][T11285] free_unref_page_list+0x84/0x378 >>>>>> [ 261.214400][T11285] shrink_folio_list+0x1234/0x13e4 >>>>>> [ 261.214409][T11285] evict_folios+0x1458/0x19b4 >>>>>> [ 261.214417][T11285] try_to_shrink_lruvec+0x1c8/0x264 >>>>>> [ 261.214422][T11285] shrink_one+0xa8/0x234 >>>>>> [ 261.214427][T11285] shrink_node+0xb38/0xde0 >>>>>> [ 261.214432][T11285] balance_pgdat+0x7a4/0xdb4 >>>>>> [ 261.214437][T11285] kswapd+0x290/0x4e4 >>>>>> [ 261.214442][T11285] kthread+0x114/0x1bc >>>>>> [ 261.214459][T11285] ret_from_fork+0x10/0x20 >>>>>> [ 261.214477][T11285] ------------[ cut here ]------------ >>>>>> [ 261.214480][T11285] WARNING: CPU: 3 PID: 11285 at mm/rmap.c:1305 >>>>>> folio_add_anon_rmap_ptes+0x2b4/0x330 >>>>>> >>>>>> [ 261.215403][T11285] pstate: 63400005 (nZCv daif +PAN -UAO +TCO +DIT >>>>>> -SSBS BTYPE=--) >>>>>> [ 261.215423][T11285] pc : folio_add_anon_rmap_ptes+0x2b4/0x330 >>>>>> [ 261.215428][T11285] lr : folio_add_anon_rmap_ptes+0x2b4/0x330 >>>>>> [ 261.215433][T11285] sp : ffffffc0a7dbbbf0 >>>>>> [ 261.215437][T11285] x29: ffffffc0a7dbbbf0 x28: ffffff8040860a08 >>>>>> x27: ffffff80db480000 >>>>>> [ 261.215445][T11285] x26: fffffffe04cc2980 x25: ffffff808f77f120 >>>>>> x24: 0000007b44941000 >>>>>> [ 261.215452][T11285] x23: 0000000000000001 x22: 0000000000000001 >>>>>> x21: fffffffe04cc2980 >>>>>> [ 261.215459][T11285] x20: ffffff80db480000 x19: fffffffe04cc2980 >>>>>> x18: ffffffed011dae80 >>>>>> [ 261.215465][T11285] x17: 0000000000000001 x16: ffffffffffffffff >>>>>> x15: 0000000000000004 >>>>>> [ 261.215471][T11285] x14: ffffff82fb73fac0 x13: 0000000000000003 >>>>>> x12: 0000000000000003 >>>>>> [ 261.215476][T11285] x11: 00000000fffeffff x10: c0000000fffeffff x9 >>>>>> : 0d46c0889b468e00 >>>>>> [ 261.215483][T11285] x8 : 0d46c0889b468e00 x7 : 545b5d3935343431 x6 >>>>>> : 322e31363220205b >>>>>> [ 261.215489][T11285] x5 : ffffffed013de407 x4 : ffffffed00698967 x3 >>>>>> : 0000000000000000 >>>>>> [ 261.215495][T11285] x2 : 0000000000000000 x1 : ffffffc0a7dbb8c0 x0 >>>>>> : ffffff8068c15c80 >>>>>> [ 261.215501][T11285] Call trace: >>>>>> [ 261.215504][T11285] folio_add_anon_rmap_ptes+0x2b4/0x330 >>>>>> [ 261.215509][T11285] __arm64_sys_swapoff+0x8cc/0x14b0 >>>>>> [ 261.215516][T11285] invoke_syscall+0x58/0x114 >>>>>> [ 261.215526][T11285] el0_svc_common+0xac/0xe0 >>>>>> [ 261.215532][T11285] do_el0_svc+0x1c/0x28 >>>>>> [ 261.215539][T11285] el0_svc+0x38/0x68 >>>>>> [ 261.215544][T11285] el0t_64_sync_handler+0x68/0xbc >>>>>> [ 261.215548][T11285] el0t_64_sync+0x1a8/0x1ac >>>>>> [ 261.215552][T11285] ---[ end trace 0000000000000000 ]--- >>>>> >>>>> Ah, yes. in unuse_pte(), you'll have to do the right thing if >>>>> !folio_test(anon) before doing the folio_add_anon_rmap_pte(). >>>>> >>>>> You might have a fresh anon folio in the swapcache that was never mapped >>>>> (hopefully order-0, otherwise we'd likely be in trouble). >>>> >>>> Yes. It is order-0 >>>> >>>> [ 261.214260][T11285] page last allocated via order 0, migratetype >>>> >>>> Otherwise, we would have encountered this VM_WARN_ON_FOLIO? >>>> >>>> __folio_add_anon_rmap() >>>> { >>>> ... >>>> VM_WARN_ON_FOLIO(folio_test_large(folio) && >>>> level != RMAP_LEVEL_PMD, folio); >>>> ... >>>> } >>>> >>>> Given that nobody has ever reported this warning, I assume all callers >>>> using folio_add_anon_rmap_pte(s) are right now safe to move to ? >>> >>> Yes, and we should likely add a VM_WARN_ON_ONCE() here that we have a >>> small folio if !anon. If that ever changes, we can assess the situation. >>> >> >> this patch actually has a WARN_ON for all !anon, so it extends the WARN >> to small. Not what I mean, see below: >> >> - if (unlikely(!folio_test_anon(folio))) { >> - VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); >> - /* >> - * For a PTE-mapped large folio, we only know that the single >> - * PTE is exclusive. Further, __folio_set_anon() might not get >> - * folio->index right when not given the address of the head >> - * page. >> - */ >> - VM_WARN_ON_FOLIO(folio_test_large(folio) && >> - level != RMAP_LEVEL_PMD, folio); >> - __folio_set_anon(folio, vma, address, >> - !!(flags & RMAP_EXCLUSIVE)); >> - } else if (likely(!folio_test_ksm(folio))) { >> + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); >> + >> >>> Only swap created "new" anon folios without properly calling the right >>> function so far, all other code handles that correctly. > > as I assume patch2/3 should have moved all !anon to > folio_add_new_anon_rmap() > > diff --git a/mm/ksm.c b/mm/ksm.c > index d2641bc2efc9..c913ba8c37eb 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -1420,7 +1420,14 @@ static int replace_page(struct vm_area_struct > *vma, struct page *page, > */ > if (!is_zero_pfn(page_to_pfn(kpage))) { > folio_get(kfolio); > - folio_add_anon_rmap_pte(kfolio, kpage, vma, addr, RMAP_NONE); > + /* > + * We currently ensure that new folios cannot be partially > + * exclusive: they are either fully exclusive or fully shared. > + */ > + if (!folio_test_anon(kfolio)) > + folio_add_new_anon_rmap(kfolio, vma, addr, RMAP_NONE); > + else > + folio_add_anon_rmap_pte(kfolio, kpage, vma, > addr, RMAP_NONE); I don't think that is required? We are only working with anon folios. Or were you able to trigger this? (which would be weird) [...] > - folio_add_anon_rmap_pte(folio, page, vma, addr, rmap_flags); > + /* > + * We currently ensure that new folios cannot be partially > + * exclusive: they are either fully exclusive or fully shared. > + */ > + if (!folio_test_anon(folio)) Here I suggest changing the comment to (and adding the VM_WARN_ON_ONCE): /* * We currently only expect small !anon folios, for which we now that * they are either fully exclusive or fully shared. If we ever get large * folios here, we have to be careful. */ if (!folio_test_anon(folio) { VM_WARN_ON_ONCE(folio_test_large(folio)); folio_add_new_anon_rmap(folio, vma, addr, rmap_flags); } else { ... -- Cheers, David / dhildenb