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 1080A42BE9F for ; Wed, 15 Jul 2026 09:30:33 +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=1784107836; cv=none; b=jAL+rKcZcH3cIFe7dxi1KXjUFygKPLHKXAAiW69KblYOmJ1vx+4+sfVu9T4tkrSOz6bTT2CrjoW1OjVCOZ0Uj9Zp8M3KUr3gf6Du6taiy93sVJ9YeGhpdMZu4ybpgbov2CN6smlHSvUBHZm+VEsbBB9Vh5x1+vCSvyJ2EdPs6pg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784107836; c=relaxed/simple; bh=6Asi0oR0FebC7fhmp3qEwY/+INQvyoe1ctYsjE7f8vw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z9f9ZehoZ2/IJUOb0dIlQ2NAM1LsIXbpd54I/Fp7rSt2ctAzlW8YbZyBWUrEJekWRC69sFqbRqDSYGiJBD2UJ1ctb8eiCf9EbQG0XnBVD3xFK4uurjAEkjrmJxeYxrYLbqZbR9NxAZbe1vH3cPVTE/oRNHhwg0QAHV364YipYOI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LyyhsV9w; 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="LyyhsV9w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C29191F000E9; Wed, 15 Jul 2026 09:30:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784107832; bh=SxmBN2YyPQXkR0PveykDVKFXZD0EBVAJwRMkvKAPslI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LyyhsV9w+Zck/2I7SvrMxnOufubJ0ASkafhPmxiOZjBd3yGkk93mzuT4TawSfawR6 JG3WQIWonJzy4ZrhYPsRUWEOkWqpfwF4JtbrfaJFl8hupjyWww5GdT8faE7VPYZKPg CDt7fm+ecyEyJATuXNWGsDBNQ2hjNyYkLE5H19OIUoDByin4tm/5d6U7by7s7iEJgf 1+l6s8P8inVhGAhGEXFE4BtI4Z04ZCjs2hJxH+i1LivAXNjA7aHklMNLU3qwAbMbRz KxjDRoGlZaSIkns3J275fIJqX0J4F+HxrmSClq5gUozsgsVbt1RcQqWZu3zhpnDHlN R24jcU39EhKrg== Message-ID: Date: Wed, 15 Jul 2026 11:30:27 +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 mm-unstable v1 2/3] mm/migrate.c: Prevent folio splitting from interacting with KSM To: Nico Pache , Usama Arif , Zi Yan , ljs@kernel.org Cc: xu.xin16@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org, usamaarif642@gmail.com, yuzhao@google.com, aarcange@redhat.com, akpm@linux-foundation.org, chengming.zhou@linux.dev, baolin.wang@linux.alibaba.com, liam@infradead.org, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com References: <18102ABA-0D8E-4DA0-AC30-544E34E445D5@nvidia.com> <20260609172719.803537-1-usama.arif@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/15/26 06:05, Nico Pache wrote: > On Tue, Jun 9, 2026 at 11:27 AM Usama Arif wrote: >> >> On Tue, 09 Jun 2026 10:07:20 -0400 Zi Yan wrote: >> >>> > > This would be a good intermediate solution while allowing backward > compatibility. And an absolute horrible user-visible toggle :) > >>> >>> Just think out loud. Or just skip huge pages all the time unless memory pressure >>> is present. Basically treat KSM as a way of reducing memory pressure by merging >>> pages. > > Hmm interesting. We should decide on future changes before committing > to one direction; however, i think the immediate solution would be > what I currently have prepped for v2. > > My v2 follows my RFC alternative approach: skip zeropage remapping if > the split comes from KSM. It also contains the patch (3) from this > version, which skips zeropage remapping if the shrinker is disabled. > >> >> I do agree with this. I questioned about if it even makes sense to split THP >> with KSM in RFC (https://lore.kernel.org/all/20260510114001.600681-1-usama.arif@linux.dev/) > > This is indeed a good question but I don't know the right solution. > > Perhaps we can discuss it here. > > So far here are the potential solutions: > a) skip zeropage remapping if the split comes from KSM > b) skip zeropage remapping completely if the shrinker is disabled > c) Disable KSM THP splitting completely > d) add a skip_huge_page sysfs toggle > e) only scan THPs when memory pressure is present > > (a)+(b) would be my V2 which I can send out whenever. > > (c) is the nuclear option, but perhaps KSM for THP is rather > inefficient and pointless > > (d) could be used with (a) and (b) and allows more flexibility than (c) > > (e) is a more dynamic approach, and could be combined with (b) and (d) > > Let me know what you think :) Where does the current patch set fall into and what's the problem with it? -- Cheers, David