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[2003:cb:c707:3500:5cd0:78d9:ca49:21f3]) by smtp.gmail.com with ESMTPSA id 11-20020a05600c020b00b00412d68dbf75sm5152399wmi.35.2024.03.08.01.03.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Mar 2024 01:03:07 -0800 (PST) Message-ID: <4392e407-b9cf-4785-a926-3eb143708260@redhat.com> Date: Fri, 8 Mar 2024 10:03:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: prohibit the last subpage from reusing the entire large folio To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: minchan@kernel.org, fengwei.yin@intel.com, linux-kernel@vger.kernel.org, mhocko@suse.com, peterx@redhat.com, ryan.roberts@arm.com, shy828301@gmail.com, songmuchun@bytedance.com, wangkefeng.wang@huawei.com, xiehuan09@gmail.com, zokeefe@google.com, chrisl@kernel.org, yuzhao@google.com, Barry Song , Lance Yang References: <20240308085653.124180-1-21cnbao@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: <20240308085653.124180-1-21cnbao@gmail.com> 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: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: C505840016 X-Stat-Signature: 6a8jr7nij555j6hx7mhi31fcdzj9d35f X-HE-Tag: 1709888593-687541 X-HE-Meta: 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 D+kUgn2e 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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 08.03.24 09:56, Barry Song wrote: > From: Barry Song > > In a Copy-on-Write (CoW) scenario, the last subpage will reuse the entire > large folio, resulting in the waste of (nr_pages - 1) pages. This wasted > memory remains allocated until it is either unmapped or memory > reclamation occurs. > > The following small program can serve as evidence of this behavior > > main() > { > #define SIZE 1024 * 1024 * 1024UL > void *p = malloc(SIZE); > memset(p, 0x11, SIZE); > if (fork() == 0) > _exit(0); > memset(p, 0x12, SIZE); > printf("done\n"); > while(1); > } > > For example, using a 1024KiB mTHP by: > echo always > /sys/kernel/mm/transparent_hugepage/hugepages-1024kB/enabled > > (1) w/o the patch, it takes 2GiB, > > Before running the test program, > / # free -m > total used free shared buff/cache available > Mem: 5754 84 5692 0 17 5669 > Swap: 0 0 0 > > / # /a.out & > / # done > > After running the test program, > / # free -m > total used free shared buff/cache available > Mem: 5754 2149 3627 0 19 3605 > Swap: 0 0 0 > > (2) w/ the patch, it takes 1GiB only, > > Before running the test program, > / # free -m > total used free shared buff/cache available > Mem: 5754 89 5687 0 17 5664 > Swap: 0 0 0 > > / # /a.out & > / # done > > After running the test program, > / # free -m > total used free shared buff/cache available > Mem: 5754 1122 4655 0 17 4632 > Swap: 0 0 0 > > This patch migrates the last subpage to a small folio and immediately > returns the large folio to the system. It benefits both memory availability > and anti-fragmentation. > > Cc: David Hildenbrand > Cc: Ryan Roberts > Cc: Lance Yang > Signed-off-by: Barry Song > --- > mm/memory.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index e17669d4f72f..0200bfc15f94 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3523,6 +3523,14 @@ static bool wp_can_reuse_anon_folio(struct folio *folio, > folio_unlock(folio); > return false; > } > + /* > + * If the last subpage reuses the entire large folio, it would > + * result in a waste of (nr_pages - 1) pages > + */ > + if (folio_ref_count(folio) == 1 && folio_test_large(folio)) { > + folio_unlock(folio); > + return false; > + } > /* > * Ok, we've got the only folio reference from our mapping > * and the folio is locked, it's dark out, and we're wearing Why not simply: diff --git a/mm/memory.c b/mm/memory.c index e17669d4f72f7..46d286bd450c6 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3498,6 +3498,10 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf, struct folio *folio) static bool wp_can_reuse_anon_folio(struct folio *folio, struct vm_area_struct *vma) { + + if (folio_test_large(folio)) + return false; + /* * We have to verify under folio lock: these early checks are * just an optimization to avoid locking the folio and freeing We could only possibly succeed if we are the last one mapping a PTE either way. No we simply give up right away for the time being. -- Cheers, David / dhildenb