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[2003:d8:2f19:9c00:568:7df7:e1:293d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-452730b9b3esm15826005e9.25.2025.06.06.03.08.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jun 2025 03:08:48 -0700 (PDT) Message-ID: <63145e68-76f7-44a1-b3fb-1213eaa959d0@redhat.com> Date: Fri, 6 Jun 2025 12:08:47 +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 1/1] mm/ksm: add ksm_pages_sharing for each process to calculate profit more accurately To: Longlong Xia , akpm@linux-foundation.org, xu.xin16@zte.com.cn Cc: chengming.zhou@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Stefan Roesch References: <20250606070314.3028593-1-xialonglong@kylinos.cn> 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: <20250606070314.3028593-1-xialonglong@kylinos.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06.06.25 09:03, Longlong Xia wrote: CCing Stefan. > The general_profit_show() function only considers ksm_pages_sharing, > while ksm_process_profit() includes both ksm_pages_sharing and > ksm_pages_shared for each process. This leads to a mismatch between > the total profits from ksm_process_profit() and general_profit_show(). > > Based on my tests, the sum of ksm_process_profit() for all processes > can be up to 20% higher than general_profit_show(), depending on > the size of page_shared. For individual processes, the ratio of > ksm_pages_sharing to ksm_merging_pages is usually not equal to 1. > > To resolve this, we suggest introducing ksm_pages_sharing for each > process to accurately calculate its pages_sharing, ensuring > ksm_process_profit() reflects shared memory benefits more accurately. > > Add a new proc file named as ksm_pages_sharing both under /proc// It's an entry in the file, not a new file. > and /proc/self/ksm_stat/ to indicate the saved pages of this process. > (not including ksm_zero_pages) Curious, why is updating ksm_process_profit() insufficient and we also have to expose ksm_pages_sharing? > > Suggested-by: Xu Xin > Signed-off-by: Longlong Xia > --- > Documentation/admin-guide/mm/ksm.rst | 5 +++-- > Documentation/filesystems/proc.rst | 8 ++++++++ > fs/proc/base.c | 18 ++++++++++++++++++ > include/linux/mm_types.h | 5 +++++ > mm/ksm.c | 12 ++++++++---- > 5 files changed, 42 insertions(+), 6 deletions(-) > > diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst > index ad8e7a41f3b5..0b33ef98930f 100644 > --- a/Documentation/admin-guide/mm/ksm.rst > +++ b/Documentation/admin-guide/mm/ksm.rst > @@ -256,9 +256,10 @@ several times, which are unprofitable memory consumed. > process_profit =~ ksm_saved_pages * sizeof(page) - > ksm_rmap_items * sizeof(rmap_item). > > - where ksm_saved_pages equals to the sum of ``ksm_merging_pages`` and > + where ksm_saved_pages equals to the sum of ``ksm_pages_sharing`` and > ``ksm_zero_pages``, both of which are shown under the directory > - ``/proc//ksm_stat``, and ksm_rmap_items is also shown in > + ``/proc//ksm_stat``, ksm_merging_pages and ksm_rmap_items are > + also shown in > ``/proc//ksm_stat``. The process profit is also shown in > ``/proc//ksm_stat`` as ksm_process_profit. > > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst > index 2a17865dfe39..e14ea8389500 100644 > --- a/Documentation/filesystems/proc.rst > +++ b/Documentation/filesystems/proc.rst > @@ -2290,6 +2290,7 @@ Example > / # cat /proc/self/ksm_stat > ksm_rmap_items 0 > ksm_zero_pages 0 > + ksm_pages_sharing 0 > ksm_merging_pages 0 > ksm_process_profit 0 > ksm_merge_any: no > @@ -2312,6 +2313,13 @@ ksm_zero_pages > When /sys/kernel/mm/ksm/use_zero_pages is enabled, it represent how many > empty pages are merged with kernel zero pages by KSM. > > +ksm_pages_sharing > +^^^^^^^^^^^^^^^^^ > + > +It represents how many pages saved of this process. > +(not including ksm_zero_pages). It is the same with what > +/proc//ksm_pages_sharing shows. > +> ksm_merging_pages > ^^^^^^^^^^^^^^^^^ > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index c667702dc69b..327bf82acf54 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -3262,6 +3262,21 @@ static int proc_pid_ksm_merging_pages(struct seq_file *m, struct pid_namespace * > > return 0; > } > + > +static int proc_pid_ksm_pages_sharing(struct seq_file *m, struct pid_namespace *ns, > + struct pid *pid, struct task_struct *task) > +{ > + struct mm_struct *mm; > + > + mm = get_task_mm(task); > + if (mm) { > + seq_printf(m, "%lu\n", mm->ksm_pages_sharing); > + mmput(mm); > + } > + > + return 0; > +} > + > static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns, > struct pid *pid, struct task_struct *task) > { > @@ -3272,6 +3287,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns, > if (mm) { > seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items); > seq_printf(m, "ksm_zero_pages %ld\n", mm_ksm_zero_pages(mm)); > + seq_printf(m, "ksm_pages_sharing %lu\n", mm->ksm_pages_sharing); > seq_printf(m, "ksm_merging_pages %lu\n", mm->ksm_merging_pages); > seq_printf(m, "ksm_process_profit %ld\n", ksm_process_profit(mm)); > seq_printf(m, "ksm_merge_any: %s\n", > @@ -3421,6 +3437,7 @@ static const struct pid_entry tgid_base_stuff[] = { > ONE("seccomp_cache", S_IRUSR, proc_pid_seccomp_cache), > #endif > #ifdef CONFIG_KSM > + ONE("ksm_pages_sharing", S_IRUSR, proc_pid_ksm_pages_sharing), > ONE("ksm_merging_pages", S_IRUSR, proc_pid_ksm_merging_pages), > ONE("ksm_stat", S_IRUSR, proc_pid_ksm_stat), > #endif > @@ -3758,6 +3775,7 @@ static const struct pid_entry tid_base_stuff[] = { > ONE("seccomp_cache", S_IRUSR, proc_pid_seccomp_cache), > #endif > #ifdef CONFIG_KSM > + ONE("ksm_pages_sharing", S_IRUSR, proc_pid_ksm_pages_sharing), > ONE("ksm_merging_pages", S_IRUSR, proc_pid_ksm_merging_pages), > ONE("ksm_stat", S_IRUSR, proc_pid_ksm_stat), > #endif > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index d6b91e8a66d6..d260cb09c10a 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -1176,6 +1176,11 @@ struct mm_struct { > * merging (not including ksm_zero_pages). > */ > unsigned long ksm_merging_pages; > + /* > + * Represents how many pages saved of this process. > + * (not including ksm_zero_pages). > + */ > + unsigned long ksm_pages_sharing; > /* > * Represent how many pages are checked for ksm merging > * including merged and not merged. > diff --git a/mm/ksm.c b/mm/ksm.c > index 8583fb91ef13..c2d85ea07b1c 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -824,6 +824,7 @@ static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node) > hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { > if (rmap_item->hlist.next) { > ksm_pages_sharing--; > + rmap_item->mm->ksm_pages_sharing--; > trace_ksm_remove_rmap_item(stable_node->kpfn, rmap_item, rmap_item->mm); > } else { > ksm_pages_shared--; > @@ -976,8 +977,10 @@ static void remove_rmap_item_from_tree(struct ksm_rmap_item *rmap_item) > folio_unlock(folio); > folio_put(folio); > > - if (!hlist_empty(&stable_node->hlist)) > + if (!hlist_empty(&stable_node->hlist)) { > ksm_pages_sharing--; > + rmap_item->mm->ksm_pages_sharing--; > + } Hm, I am wondering if that works. Stable nodes are not per MM, so can't we create an accounting imbalance for one MM somehow? (did not look into all the details, just something that came to mind) -- Cheers, David / dhildenb