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 8DBE92A1CF; Tue, 16 Sep 2025 04:33:11 +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=1757997191; cv=none; b=NbQ0nVWWm7IdA5iFchW2rzMGTxfNi/SAy2ODhlweg3HAfyhDNZgjhXew/up9wWK1bis+vgB67a/u4nNrQT0nVPEXKu92ENW+TTMEYGizmKJe/nC6deUe/8cHCHxC6+ARPOSKJb8zvaV1N+Xae4snUTQLBZkkQCUFTkOvjmB1F/M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757997191; c=relaxed/simple; bh=XUv2PggEgcd7aiSvIefqjmLXrdWBq5ZtfvsjcSnF6Ts=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jlZLfVGQksd9lEltBSL+p0VvyboS07thVd68EeiQqzjYLwWBfp8yYah5LVJMJskKjKcjUC2K48kwYklfoyE4RwI/6lfedLeKHUihsipoIH2gp8HPVa/1ZEm569yXaYWbHUwD/JPhoGllLlYZvZYGJG0T3Pgp9WKtpx+C8UqE1UU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UA4pT+Xx; 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="UA4pT+Xx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA138C4CEEB; Tue, 16 Sep 2025 04:33:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757997191; bh=XUv2PggEgcd7aiSvIefqjmLXrdWBq5ZtfvsjcSnF6Ts=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=UA4pT+XxdcvTwEXm0XQVMVK4IeeqDbY7dO/AZA7fAeL9BZlVOrkBtl9586nWqhkit fEkVxPoPy009mzMJg2WqrM7m5GFCL161QrthTG+XB1OHtQ/sncY+fKBcq9IWtfaFdv 4Zos33vOsW2M9yPRjEznTzzxr6vPBWDL5Kiopuql9MOcVGBJ3PrzJOA0RiPiJMwGDp TX3sx9Sqd43Lm344yY4+U2wvV5fYdb00S3j/giclSX62pecxjwbq0lkY/wEzyO2LJQ 8bJ7BpxlVNzY/ZtqSab19+Ggpge+n2hOyyJq1VzrYQhCdqldnvwgAa+ANrZJo8Y+Cu zrQw1c1t8/Kmg== Date: Tue, 16 Sep 2025 00:33:09 -0400 From: Sasha Levin To: Andrew Morton Cc: Donet Tom , David Hildenbrand , Ritesh Harjani , Xu Xin , Chengming Zhou , Wei Yang , Aboorva Devarajan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Giorgi Tchankvetadze , stable@vger.kernel.org, Joe Perches Subject: Re: [PATCH v2 1/3] mm/ksm: Fix incorrect KSM counter handling in mm_struct during fork Message-ID: References: <4044e7623953d9f4c240d0308cf0b2fe769ee553.1757946863.git.donettom@linux.ibm.com> <20250915164248.788601c4dc614913081ec7d7@linux-foundation.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20250915164248.788601c4dc614913081ec7d7@linux-foundation.org> On Mon, Sep 15, 2025 at 04:42:48PM -0700, Andrew Morton wrote: >On Mon, 15 Sep 2025 20:33:04 +0530 Donet Tom wrote: > >> Currently, the KSM-related counters in `mm_struct`, such as >> `ksm_merging_pages`, `ksm_rmap_items`, and `ksm_zero_pages`, are >> inherited by the child process during fork. This results in inconsistent >> accounting. >> >> When a process uses KSM, identical pages are merged and an rmap item is >> created for each merged page. The `ksm_merging_pages` and >> `ksm_rmap_items` counters are updated accordingly. However, after a >> fork, these counters are copied to the child while the corresponding >> rmap items are not. As a result, when the child later triggers an >> unmerge, there are no rmap items present in the child, so the counters >> remain stale, leading to incorrect accounting. >> >> A similar issue exists with `ksm_zero_pages`, which maintains both a >> global counter and a per-process counter. During fork, the per-process >> counter is inherited by the child, but the global counter is not >> incremented. Since the child also references zero pages, the global >> counter should be updated as well. Otherwise, during zero-page unmerge, >> both the global and per-process counters are decremented, causing the >> global counter to become inconsistent. >> >> To fix this, ksm_merging_pages and ksm_rmap_items are reset to 0 >> during fork, and the global ksm_zero_pages counter is updated with the >> per-process ksm_zero_pages value inherited by the child. This ensures >> that KSM statistics remain accurate and reflect the activity of each >> process correctly. >> >> Fixes: 7609385337a4 ("ksm: count ksm merging pages for each process") > >Linux-v5.19 > >> Fixes: cb4df4cae4f2 ("ksm: count allocated ksm rmap_items for each process") > >Linux-v6.1 > >> Fixes: e2942062e01d ("ksm: count all zero pages placed by KSM") > >Linux-v6.10 > >> cc: stable@vger.kernel.org # v6.6 > >So how was Linux-v6.6 arrived at? e2942062e01d is in v6.6, not in v6.10 - I suspect that this is why the "# v6.6" part was added. >I think the most important use for Fixes: is to tell the -stable >maintainers which kernel version(s) we believe should receive the >patch. So listing multiple Fixes: targets just causes confusion. Right - there's no way of communicating if all the commits listed in multiple Fixes tags should exist in the tree, or any one of them, for the new fix to be applicable. -- Thanks, Sasha