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[91.12.107.195]) by smtp.gmail.com with ESMTPSA id d34-20020a0565123d2200b0051ef1d658bcsm2530237lfv.51.2024.05.08.05.36.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 May 2024 05:36:28 -0700 (PDT) Message-ID: <7cac6762-4486-4c42-885d-dd5715eb6ba4@redhat.com> Date: Wed, 8 May 2024 14:36:26 +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 2/4] mm/ksm: fix ksm_zero_pages accounting To: Chengming Zhou , Andrew Morton , Stefan Roesch , xu xin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com References: <20240508-b4-ksm-counters-v1-0-e2a9b13f70c5@linux.dev> <20240508-b4-ksm-counters-v1-2-e2a9b13f70c5@linux.dev> 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: <20240508-b4-ksm-counters-v1-2-e2a9b13f70c5@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 08.05.24 11:55, Chengming Zhou wrote: > We normally ksm_zero_pages++ in ksmd when page is merged with zero page, > but ksm_zero_pages-- is done from page tables side, which can't protected > by the ksmd mutex. > > So we can read very exceptional value of ksm_zero_pages in rare cases, > such as -1, which is very confusing to users. > > Fix it by changing to use atomic_long_t, and the same case with the > mm->ksm_zero_pages. > > Signed-off-by: Chengming Zhou > --- > fs/proc/base.c | 2 +- > include/linux/ksm.h | 22 +++++++++++++++++++--- > include/linux/mm_types.h | 2 +- > mm/ksm.c | 11 +++++------ > 4 files changed, 26 insertions(+), 11 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 18550c071d71..72a1acd03675 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -3214,7 +3214,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns, > mm = get_task_mm(task); > if (mm) { > seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items); > - seq_printf(m, "ksm_zero_pages %lu\n", mm->ksm_zero_pages); > + seq_printf(m, "ksm_zero_pages %ld\n", mm_ksm_zero_pages(mm)); > seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages); > seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm)); > mmput(mm); > diff --git a/include/linux/ksm.h b/include/linux/ksm.h > index 52c63a9c5a9c..bfc2cf756b0d 100644 > --- a/include/linux/ksm.h > +++ b/include/linux/ksm.h > @@ -33,16 +33,32 @@ void __ksm_exit(struct mm_struct *mm); > */ > #define is_ksm_zero_pte(pte) (is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte)) > > -extern unsigned long ksm_zero_pages; > +extern atomic_long_t ksm_zero_pages; > + > +static inline void ksm_map_zero_page(struct mm_struct *mm) > +{ > + atomic_long_inc(&ksm_zero_pages); > + atomic_long_inc(&mm->ksm_zero_pages); > +} > > static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte) > { > if (is_ksm_zero_pte(pte)) { > - ksm_zero_pages--; > - mm->ksm_zero_pages--; > + atomic_long_dec(&ksm_zero_pages); > + atomic_long_dec(&mm->ksm_zero_pages); > } > } > > +static inline long get_ksm_zero_pages(void) > +{ > + return atomic_long_read(&ksm_zero_pages); > +} I suggest inlining that one. The naming of the function also is a bit inconsistent staring at the others. > + > +static inline long mm_ksm_zero_pages(struct mm_struct *mm) > +{ > + return atomic_long_read(&mm->ksm_zero_pages); > +} > + Apart from that LGTM Acked-by: David Hildenbrand -- Cheers, David / dhildenb