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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4771e12cb2asm52407195e9.0.2025.10.29.07.46.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Oct 2025 07:46:36 -0700 (PDT) Message-ID: Date: Wed, 29 Oct 2025 15:46:36 +0100 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 3/3] ksm: replace function unmerge_ksm_pages with break_ksm To: Pedro Demarchi Gomes , Andrew Morton Cc: Xu Xin , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251028131945.26445-1-pedrodemargomes@gmail.com> <20251028131945.26445-4-pedrodemargomes@gmail.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20251028131945.26445-4-pedrodemargomes@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 28.10.25 14:19, Pedro Demarchi Gomes wrote: > Function unmerge_ksm_pages() is unnecessary since now break_ksm() walks > an address range. So replace it with break_ksm(). > > Suggested-by: David Hildenbrand > Signed-off-by: Pedro Demarchi Gomes > --- > mm/ksm.c | 39 ++++++++++++++++----------------------- > 1 file changed, 16 insertions(+), 23 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 1d1ef0554c7c..18c9e3bda285 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -669,6 +669,18 @@ static const struct mm_walk_ops break_ksm_lock_vma_ops = { > }; > > /* > + * Though it's very tempting to unmerge rmap_items from stable tree rather > + * than check every pte of a given vma, the locking doesn't quite work for > + * that - an rmap_item is assigned to the stable tree after inserting ksm > + * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing > + * rmap_items from parent to child at fork time (so as not to waste time > + * if exit comes before the next scan reaches it). > + * > + * Similarly, although we'd like to remove rmap_items (so updating counts > + * and freeing memory) when unmerging an area, it's easier to leave that > + * to the next pass of ksmd - consider, for example, how ksmd might be > + * in cmp_and_merge_page on one of the rmap_items we would be removing. > + * > * We use break_ksm to break COW on a ksm page by triggering unsharing, > * such that the ksm page will get replaced by an exclusive anonymous page. > * > @@ -1077,25 +1089,6 @@ static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list) > } > } > > -/* > - * Though it's very tempting to unmerge rmap_items from stable tree rather > - * than check every pte of a given vma, the locking doesn't quite work for > - * that - an rmap_item is assigned to the stable tree after inserting ksm > - * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing > - * rmap_items from parent to child at fork time (so as not to waste time > - * if exit comes before the next scan reaches it). > - * > - * Similarly, although we'd like to remove rmap_items (so updating counts > - * and freeing memory) when unmerging an area, it's easier to leave that > - * to the next pass of ksmd - consider, for example, how ksmd might be > - * in cmp_and_merge_page on one of the rmap_items we would be removing. > - */ > -static int unmerge_ksm_pages(struct vm_area_struct *vma, > - unsigned long start, unsigned long end, bool lock_vma) > -{ > - return break_ksm(vma, start, end, lock_vma); > -} > - > static inline > struct ksm_stable_node *folio_stable_node(const struct folio *folio) > { > @@ -1233,7 +1226,7 @@ static int unmerge_and_remove_all_rmap_items(void) > for_each_vma(vmi, vma) { > if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) > continue; > - err = unmerge_ksm_pages(vma, > + err = break_ksm(vma, > vma->vm_start, vma->vm_end, false); Move that all into a single line. With that Acked-by: David Hildenbrand Thanks for tackling this! -- Cheers David / dhildenb