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 6572F40BCBC for ; Tue, 8 Sep 2026 11:55:03 +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=1788868504; cv=none; b=nJw6mO3yq4b/5utDia8+470xdI7SiudXSZSfb63/hUPiAkQWoSKJeWvJEUJglvgtoqIaLuMBYNL60iTVWrXZDlMbLHkH8LAyTfe3VxrxnNXZ6A6QL+Xs1ar4hDUY/yghaW9LrZGIUV0tS2hvniJu5pgc6I8zXcGU4eRPZEdxP9Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788868504; c=relaxed/simple; bh=vSwPl4QbnbnFWmj+AcDas4V0ov5zQlYQbWMorXWOeqI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Fxjh/DnMhmNvOLh/LOZd292QPAnTWkT30fNiFYvEERJBDGuDMC6sVLuy1bkZRcz41ocfKOScWKDkV05YmT2cJEdTctDki3K02ui4NhrEyaUKKJSQJlbdq1blpKdqph6Rgifn/XB36+Xqi8gE1+Kq02BAORQq4yojcLRRErA4WS8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=O3u+q7i6; 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="O3u+q7i6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A4B91F00A3A; Tue, 8 Sep 2026 11:54:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788868503; bh=A8fGRJH1FYroE0NYq5pSQ/cdoutdIPA6KQGFv2lno1c=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=O3u+q7i6QeyYtTqdVxTUmL8k11LRAGHiZTHWhr6k+T3QWv6q7uS4HDzW9FXq1Vocr SfFiOd7fqggCnDd2KFkF97idrc43LCaE5VM4g73AC4KFodCx9IS8NVTRZ1KwUon5dx sOPyvNX1DYrdEcKIRct65bFM1sBOPHn1EK5RaRsYsZLLxKPMV52QrFC2VPhVP+HAGW wtRPwv0O3QLICXC6EzOUSW6JiBETKuWAGceK1oJLhtLPEK0ku3vozxteWTTI3oeqid wTKMiFWoWF95fUnjr0pHc3MnXao3Wsq4WWSN979SZ3M7GC0Ay8nzXRdbC638/yfE27 7hZMc/MF618PQ== Message-ID: Date: Tue, 8 Sep 2026 13:54:56 +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] mm: remove min_free_kbytes adjustment for THP Content-Language: en-US To: Nimrod Oren , Andrew Morton , David Hildenbrand , Lorenzo Stoakes Cc: Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Hugh Dickins , Nirmoy Das , Dragos Tatulea , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260901190123.3511535-1-noren@nvidia.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260901190123.3511535-1-noren@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/1/26 21:01, 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. > Commit f000565adb77 ("thp: set recommended min free kbytes") added this > heuristic to help keep pageblocks free and reduce fragmentation for THP > allocations. > > The recommendation scales poorly with larger base page sizes. With the > default arm64 pageblock sizes, the contribution per eligible zone > before applying the existing cap of 5% of low memory 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 > > Even with that cap, min_free_kbytes can reach excessive levels. > > The automatic min_free_kbytes increase predates proactive compaction > and many subsequent changes to compaction. Given those changes, > increasing min_free_kbytes for THP by default is no longer clearly > justified. > > Remove set_recommended_min_free_kbytes() and all associated > recalculation paths. With this policy gone, min_free_kbytes is > controlled only by the page allocator's default calculation and the > vm.min_free_kbytes sysctl. Users who want additional headroom may set a > higher value via that sysctl. > > Link: https://lore.kernel.org/r/20260831075635.2244437-1-noren@nvidia.com/ > Suggested-by: Michal Hocko > Signed-off-by: Nimrod Oren > --- > v3: > * Replace the 1 GiB cap with removal of the THP-driven min_free_kbytes > increase as suggested by Michal. > * Remove all associated recalculation paths. > * Make min_free_kbytes, user_min_free_kbytes, > calculate_min_free_kbytes(), and setup_per_zone_wmarks() static. > * Drop the now-unused declarations and khugepaged's page_alloc.h include. > * Drop the obsolete v2 documentation addition. > > v2: > * Use a named constant for the cap. > * Drop explicit linux/sizes.h include. > * Update min_free_kbytes documentation. > https://lore.kernel.org/r/20260831075635.2244437-1-noren@nvidia.com/ > > v1: > * Cap the final recommendation at 1 GiB as suggested by Lorenzo. > https://lore.kernel.org/r/20260728202014.2517142-1-noren@nvidia.com/ > > RFC v1: > https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ > --- > include/linux/khugepaged.h | 5 ---- > mm/huge_memory.c | 14 --------- > mm/internal.h | 8 ----- > mm/khugepaged.c | 60 -------------------------------------- > mm/page_alloc.c | 11 +++---- > mm/page_alloc.h | 2 -- > mm/shmem.c | 7 ----- > 7 files changed, 4 insertions(+), 103 deletions(-) Given neither of the patchset versions achieved universal acceptance, could we try just disabling all the automatic (re)calculations of min_free_kbytes the first moment the sysctl gets adjusted from userspace?