From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 44174C61DE2 for ; Mon, 31 Aug 2026 09:34:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 373D56B0092; Mon, 31 Aug 2026 05:34:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 325A76B0095; Mon, 31 Aug 2026 05:34:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1EE306B0096; Mon, 31 Aug 2026 05:34:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 0207A6B0092 for ; Mon, 31 Aug 2026 05:34:44 -0400 (EDT) Received: from smtpin11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 6523DA03CE for ; Mon, 31 Aug 2026 09:34:44 +0000 (UTC) X-FDA: 85161054888.11.5B53539 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf16.hostedemail.com (Postfix) with ESMTP id B33CF180004 for ; Mon, 31 Aug 2026 09:34:42 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=fsxw37uq; spf=pass (imf16.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788168882; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=4aVpTeV09tl2ZIJXldYxie5+lftJRpDlFbGafsWVa/Y=; b=GNzuQLIu4XZ13FomEuMu+NpgpHugn/XqpfN/Sry9QZoaOkugGMpjfu2pBR1r0YhT4m239+ bYMO/A7Z/Mata+BXClGoAITntsUTJcsKyWW1ZjYqPMwoyvybST3Y/WX0kbCYyQdKNsx7IQ crrLWHlTIXs23sy6coWIV9k+AIeaFaU= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788168882; b=L4GUZDUqY/5lKFCQxk6xGPZvZBK/grTOj4PV0kwrN8GkRjaJsBXOXUDFkbXQjNHzXHZQ9d q3ZFPqVihtNGrZDqEKZLRjEov1XimqTbksBQTSk6t0sMS7cpUdJ9rk7/oFqXGtQlCY4nW9 c8u2GeJ2etT2llUdQkPAIaKkgyxEfQk= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=fsxw37uq; spf=pass (imf16.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id CEF5743E3E; Mon, 31 Aug 2026 09:34:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F112D1F000E9; Mon, 31 Aug 2026 09:34:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788168881; bh=4aVpTeV09tl2ZIJXldYxie5+lftJRpDlFbGafsWVa/Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=fsxw37uqF9+SavdgCPh+An6E7UFG+cjRuxWcGRktFZqKnC4w9ip1z+JAVeBVhkIdi SIb9cJoFNYGqjO58A/yKEOqHis8UQz8bmCY2mMLESyyRz7yk+RrqdnDMhcf95sbet1 sZBl5bfeBGq1uGtDGh42TUu9GJ4cf0R+TTRqZrnk09SGAJpljX69S0ddWTs8yawEZA kjXLUSVTzV69S9x6zYSvrMAqfXxQGev/jZpEzMmEh8cJ7fkX724Y8RSOEuYLpmPjt3 A5g95G7m9P9XDTm7ynujW3M0GPlBakvCDPMGSE3IOF6knLaBtlKEN/p/mucMMbo5VR ZSN2+W1pb7ukA== Date: Mon, 31 Aug 2026 10:34:32 +0100 From: "Lorenzo Stoakes (ARM)" To: Michal Hocko Cc: Nimrod Oren , Andrew Morton , David Hildenbrand , Jonathan Corbet , Vlastimil Babka , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Shuah Khan , Randy Dunlap , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Nirmoy Das , Dragos Tatulea , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/khugepaged: cap min_free_kbytes recommendation at 1 GiB Message-ID: References: <20260831075635.2244437-1-noren@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B33CF180004 X-Stat-Signature: zr6srdx434da6jn9cyx4ujag1r13tqrb X-HE-Tag: 1788168882-242213 X-HE-Meta: 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 BN9NyDZ9 CjNHhu7mA33x+ol91IAjHGGDT+kuN0pGtfpCkOpZoH24eLA2TVC3vFqaxdGyF2zVi+5yJss3A6ObMaAibWdManyYpDc3Ve3UVmXhpDKnqPGVq7d3gowDAW5vFwShrLRuxhdPXWO2leq8R9a4TEd2gxlI6OaHLU/WtbPjiEk/iqkc2ckBJxvmBlRbTyPZzoxaVJa4tq0S0KI3QxYoV69fZxqykvW2DKznGFE+oKzQ/Z6/cl6wAoR3JZtAX/W3kjNm52At7eXRltlhj1vnrCQj2lJueRmjxMqza3Lum33Mt+PkEBhY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 31, 2026 at 11:20:30AM +0200, Michal Hocko wrote: > On Mon 31-08-26 10:56:35, Nimrod Oren wrote: > > When THP is enabled, set_recommended_min_free_kbytes() may raise > > min_free_kbytes using a heuristic that scales with pageblock_nr_pages. > > With MIGRATE_PCPTYPES equal to 3, the formula accounts for 11 > > pageblocks for every eligible populated zone before capping the result > > at 5% of low memory. > > > > This is reasonable when a pageblock is 2 MiB, as on common 4 KiB page > > configurations, but scales poorly with larger base page sizes. With > > the default arm64 pageblock sizes, the contribution per eligible zone > > before the 5% cap is: > > > > 4 KiB pages: 2 MiB pageblock, 22 MiB per zone > > 16 KiB pages: 32 MiB pageblock, 352 MiB per zone > > 64 KiB pages: 512 MiB pageblock, 5.5 GiB per zone > > > > Consequently, min_free_kbytes can reach excessive and unwanted levels. > > > > Add an absolute 1 GiB cap to the recommendation, in addition to the > > existing percentage cap. This bounds the automatic recommendation to a > > sane value on systems with large pageblocks while preserving existing > > behavior for typical systems with 2 MiB pageblocks. > > I would argue that the whole model of increasing min_free_kbytes for THP > is wrong. This will trigger memory reclaim sooner and make the THP > availability more likely but this was at times where we didn't have > pro-active compaction and many changes in the compaction. So is this > actually needed in general resp. only large pageblocks systems? Ohh even better :) I did find it strange that we increased accordingly. I'm more than happy to see this just die altogether if people agree that's a sensible way forward... > > -- > Michal Hocko > SUSE Labs -- Cheers, Lorenzo