From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 3F1DD480974 for ; Mon, 6 Jul 2026 06:49:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783320587; cv=none; b=AR0NU1hQgAFxaAIWBTeGRL/cM7OrXnSgzUMpE+S1tc7hypb5++Rb68vd+aH1VTYTyzhv48Wsi0Km0HI8BWzDkneT5RTObQ3RRoP7wrKucoWifO2PEMTWkDv2VXok9gPOBBCj5GkxGNo4GxYMIPxYNr94JPI2KpneZsT/t1d/8eM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783320587; c=relaxed/simple; bh=IyDF4idxCF7PhW7B+pO0vI+V/o9K4UqN7vgediYMKTE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HQuIyrxDbQ3lfSm8dm13p8kGMbkkon/y/D+Llgn7ExpMwOxPgMjL6z6BTQFaKIATd6hlp3bVYXpmz4UOt1Y75tDUbLbG5hRtBN7KGCSfnR5IDNDUqbUeJs+UpaTq9XcW70KxOGTc5t5eFeO/v68oo6f7KTtBTLZFyaTu9r+xlGo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UZp7lfRv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UZp7lfRv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3B2E1F000E9; Mon, 6 Jul 2026 06:49:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783320578; bh=ZtCnYnyv7Hmpt8mLmtELq780NxRlJZLQ0qZI2absRDw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=UZp7lfRv15shr5/jiCnRRh8gt6f7FZR2Voy9nBq1Wf7WL/bVFyoFGFdtnLtFZT/RW VlvsDgVXq1HJCUsIBprHl+OZ4v7RpuZmSGSgUXuJkExqqTQzP8wEri/PN+o6bct97h qFP4NRemhz/tESWdlkezBlOrw+I4SCdpLSWFkH6b8uXt2SWOCMhIuuhIm7d7aMIc9p KXEhTP01uiDoHqSd3QcZPkLToisJ6pOh0QzrjvR/VXWaDZZvF9qCpjvW4ug5Y88boy 88PB0wis58ArZBogah1C8iHnAGH8zDzCWCr75+deippDfJhEupejKo3Oe5xSmnsXgZ eMji33rOSG36w== Message-ID: Date: Mon, 6 Jul 2026 08:49:34 +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 v11 0/3] KSM: performance optimizations for rmap_walk_ksm To: xu.xin16@zte.com.cn, akpm@linux-foundation.org Cc: chengming.zhou@linux.dev, hughd@google.com, wang.yaxin@zte.com.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ljs@kernel.org References: <20260706124039747M7gtCsrOvuzDyfLMXIJ2B@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 7/6/26 06:40, xu.xin16@zte.com.cn wrote: >> Again, thanks for persisting with this. Great improvement and I'd love >> to see us get this finished off. >> >> Please have a look through the AI review: >> >> https://sashiko.dev/#/patchset/20260703162253688u8Str9eFLR8TGCmo7nIOF@zte.com.cn >> >> That 32-bit thing looks legit, kinda fatal but easy to address. >> > > Hi, Andrew, This is not a major issue. I think it's acceptable and detailed > analysis is as follows: > > The sashiko said: > " >> Looking at struct ksm_rmap_item in mm/ksm.c, the linear_page_index (unsigned >> long) is placed in a union with an anonymous struct containing oldchecksum >> (unsigned int), age (rmap_age_t, 1 byte), and remaining_skips (rmap_age_t, >> 1 byte). >> On 32-bit platforms, an unsigned long is only 4 bytes, while the anonymous >> struct is at least 6 bytes. When break_cow(), remove_node_from_stable_tree(), >> and remove_rmap_item_from_tree() assign rmap_item->linear_page_index = 0 to >> reset the age-related information, it appears this will only zero the first 4 >> bytes (clearing oldchecksum). The age and remaining_skips fields would retain >> their stale historical values from before the page was originally merged. > > Indeed, on 32-bit CPU, that patch doesn't clear age-related information, but it > doesn't introduce any issue because at this point the linear_page_index and > age-related information do not overlap, and there is no conflict between them. > This is clearly consistent with the logic before applying the patch, so there > won't be any problem. It keeps bringing that up, and we clearly document "might overlay age-related information". So just ignore this. -- Cheers, David