From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1F0262638BC for ; Wed, 8 Apr 2026 12:57:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775653034; cv=none; b=A4y94nO73TpOw293A4DLOKEDykj/K27A8JXZoSZHR+mwm9gJNDzG1R3xfl3xQotoJTZ3Arn8C3lQosPooCB7SGLHon0Tr2NPyYrPoeL4gAJ2eVzEQE5Mz0Ca/YG5Xjp6QdXuiM8RTXsaYJSAJkgEjVr5G8GfZxwyMLeiLz1q7v8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775653034; c=relaxed/simple; bh=rr1xzx2Eh6OHGsQ46VBfmOaRm2wD/OwQmkGUmzL5x/I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Nzn/zA3hzFFpH4ArWHXiXTVAD5VjYbuUgy2XR+v1DJiXu/Ip+PUXe5EWG0rHTK3l3FZ3thDhx6GXM0RVq13f01TRxz6JHW2iK5gg/jyPax0Mrfg0+gSHH6BNdrZHyw70Qt0en9vnPhL31e1+4OChhHx+XVkTzk+SEWz2BLP/Lys= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AtIJfCqK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AtIJfCqK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E70E0C19421; Wed, 8 Apr 2026 12:57:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775653033; bh=rr1xzx2Eh6OHGsQ46VBfmOaRm2wD/OwQmkGUmzL5x/I=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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 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 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 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