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b=AtIJfCqK2EPsOxsIOKQyQgg52/CWyUR1WE+DjPwboxmxtAJ3nSQXYnT8srGlgrkCg e1OafIHm9kaK65lHNPIAVCX0ylYVJIwKKlvx0Lp2XD+/zkMiGFVnvC26a9OxDdgXTB r+I2V4DhiFd6GGSGlkWUxXMiuQnhnXvf24KLBo7s6GvJ55SLXQH+b79p4FNHrVzv7a uuUB+U74YN5ey9aRgMO/GyBrOi2y3Mq+Cb+WoHntP1NvBFSzTmDsRZ3uy/axh185dk Nuv5tQkfYl6NSKR7jKhKSgoDDZP5dAfY3cZ5oTfZLffNVWruiR02l3q3BAjj9LGVJ2 JUjSo4IyajBKg== Message-ID: <8332aedb-e499-4789-8f46-832df8d60224@kernel.org> Date: Wed, 8 Apr 2026 14:57:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] ksm: Optimize rmap_walk_ksm by passing a suitable address range To: "Lorenzo Stoakes (Oracle)" , xu.xin16@zte.com.cn Cc: hughd@google.com, akpm@linux-foundation.org, chengming.zhou@linux.dev, wang.yaxin@zte.com.cn, yang.yang29@zte.com.cn, michel@lespinasse.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <9950c6c1-f960-58c0-4312-e4f5ac122043@google.com> <20260407142141059pWDasxUAknP5rqvAMl28K@zte.com.cn> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 81354C0014 X-Stat-Signature: u4md5a9n5oiqogqpyezx4sucfuieob4u X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1775653034-215385 X-HE-Meta: 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 GG2SXPvC ojP0f4EUz+J7kyLoXpZNL/GH3HUVu5tWgLZqDxKHLMSKXVJAQxPwFVF5r0k9mGFlSUqKP4PrY7jGi+zxfaXbnhGNNXe3AFf96fdRTmHZaVmz6M5xpTaPfoBv8UWRg8glfIHV8YBE31aJNG7XqV4r0aPDY2HgIkI4RSgGfpa5DrHK0C2uGgYY0PTs6r74ghfx0Fjccbb8UjX8xDN81F1f7iINq4dWhwrlEgwKgz0RmaGLPZTXLn2iNIDpbUKJ7Wbrau+EGGH7IArnURBYcswsTPaLEb+dHQtjvehBo86CzXgj4wRjH2sNV4o95cYQLGWkl63myiq9BgJvL5l30uHXnPX03bNVAT4jJvbMCS4olCr224cE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/7/26 11:36, Lorenzo Stoakes (Oracle) wrote: > On Tue, Apr 07, 2026 at 02:21:41PM +0800, xu.xin16@zte.com.cn wrote: >>> >>> I'd completely forgotten that patch by now! But it's dealing with a >>> different issue; and note how it's intentionally leaving MADV_MERGEABLE >>> on the vma itself, just using MADV_UNMERGEABLE (with &dummy) as an >>> interface to CoW the KSM pages at that time, letting them be remerged after. > > Hmm yeah, we mark them unmergeable but don't update the VMA flags (since using > &dummy), so they can just be merged later right? > > And then the: > > void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc) > { > ... > const pgoff_t pgoff = rmap_item->address >> PAGE_SHIFT; > ... > anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, > pgoff, pgoff) { > ... > } > ... > } > > Would _assume_ that folio->pgoff == addr >> PAGE_SHIFT, which will no longer be > the case here? I'm wondering whether we could figure the pgoff out, somehow, so we wouldn't have to store it elsewhere. What we need is essentially what __folio_set_anon() would have done for the original folio we replaced. folio->index = linear_page_index(vma, address); Could we obtain that from the anon_vma assigned to our rmap_item? pgoff_t pgoff; pgoff = (rmap_item->address - anon_vma->vma->vm_start) >> PAGE_SHIFT; pgoff += anon_vma->vma->vm_pgoff; It would be the same adjustment everywhere we look in child processes, because the moment they would mremap() would be where we would have unshared. Just a thought after reading avc_start_pgoff ... -- Cheers, David