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[2003:cb:c713:2a00:f151:50f1:7164:32e6]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36d2716caadsm1171764f8f.39.2024.08.08.01.51.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Aug 2024 01:51:33 -0700 (PDT) Message-ID: <03a7c798-7a0d-4873-8fcb-8940d8dadc00@redhat.com> Date: Thu, 8 Aug 2024 10:51:31 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 01/10] mm: vmscan: add validation before spliting shmem large folio To: Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, wangkefeng.wang@huawei.com, chrisl@kernel.org, ying.huang@intel.com, 21cnbao@gmail.com, ryan.roberts@arm.com, shy828301@gmail.com, ziy@nvidia.com, ioworker0@gmail.com, da.gomez@samsung.com, p.raghav@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christian Brauner , Luis Chamberlain References: <8a8c6dc9df0bc9f6f7f937bea446062be19611b3.1723012159.git.baolin.wang@linux.alibaba.com> <9b45a0dc-fa12-428a-8702-c7690c26aedc@redhat.com> <770190a2-3938-4ba9-9aaf-7320b34addf4@linux.alibaba.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: <770190a2-3938-4ba9-9aaf-7320b34addf4@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 08.08.24 04:36, Baolin Wang wrote: > > > On 2024/8/7 23:53, David Hildenbrand wrote: >> On 07.08.24 09:31, Baolin Wang wrote: >>> Page reclaim will not scan anon LRU if no swap space, however >>> MADV_PAGEOUT >>> can still split shmem large folios even without a swap device. Thus add >>> swap available space validation before spliting shmem large folio to >>> avoid redundant split. >>> >>> Signed-off-by: Baolin Wang >>> --- >>>   mm/vmscan.c | 8 ++++++++ >>>   1 file changed, 8 insertions(+) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index 31d13462571e..796f65781f4f 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1259,6 +1259,14 @@ static unsigned int shrink_folio_list(struct >>> list_head *folio_list, >>>               } >>>           } else if (folio_test_swapbacked(folio) && >>>                  folio_test_large(folio)) { >>> + >>> +            /* >>> +             * Do not split shmem folio if no swap memory >>> +             * available. >>> +             */ >>> +            if (!total_swap_pages) >>> +                goto activate_locked; >>> + >>>               /* Split shmem folio */ >>>               if (split_folio_to_list(folio, folio_list)) >>>                   goto keep_locked; >> >> Reminds me of >> >> commit 9a976f0c847b67d22ed694556a3626ed92da0422 >> Author: Luis Chamberlain >> Date:   Thu Mar 9 15:05:43 2023 -0800 >> >>     shmem: skip page split if we're not reclaiming >>     In theory when info->flags & VM_LOCKED we should not be getting >>     shem_writepage() called so we should be verifying this with a >>     WARN_ON_ONCE().  Since we should not be swapping then best to >> ensure we >>     also don't do the folio split earlier too.  So just move the check >> early >>     to avoid folio splits in case its a dubious call. >>     We also have a similar early bail when !total_swap_pages so just >> move that >>     earlier to avoid the possible folio split in the same situation. >> >> >> But indeed, pageout() -> writepage() is called *after* the split in the >> vmscan path. >> >> In that "noswap" context, I wonder if we also want to skip folios part >> of shmem >> with disabled swapping? > > Yes, I think so. > >> >> But now I am wondering under which circumstances we end up calling >> shmem_writepage() with a large folio. And I think the answer is the >> comment of >> folio_test_large(): via drivers/gpu/drm/i915/gem/i915_gem_shmem.c. >> >> >> ... so if shmem_writepage() handles+checks that, could we do >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index a332cb80e928..7dfa3d6e8ba7 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1257,11 +1257,6 @@ static unsigned int shrink_folio_list(struct >> list_head *folio_list, >>                                                 goto >> activate_locked_split; >>                                 } >>                         } >> -               } else if (folio_test_swapbacked(folio) && >> -                          folio_test_large(folio)) { >> -                       /* Split shmem folio */ >> -                       if (split_folio_to_list(folio, folio_list)) >> -                               goto keep_locked; >>                 } >> >>                 /* >> >> instead? > > Seems reasonable to me. But we should pass the 'folio_list' to > shmem_writepage() to list the subpages of the large folio. Let me try. Ah, yes, good point. Alternatively, we'd have to split and try writing all subpages in there. I wonder what to do if we fail to write some, and if we could handle that transparently, without the folio_list. -- Cheers, David / dhildenb