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 C43984B1B2D for ; Wed, 2 Sep 2026 17:01:03 +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=1788368465; cv=none; b=AMDH0iYM77ivdRkcZDOlyysIqkIqsTBPOnt2EhMja1h39RBkJYB/l4m7Ee0OBXlb1xOLYxb6OyCf34IGSE/hYat9UFSOquS4cjxpo2QjdHnRacKjUhkbLL2nWYB6VKREaSJoF3zYUIUJhmRxpFtsjJtmCvHx0SeL4djfsoyoQI8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788368465; c=relaxed/simple; bh=REz7hmB4Ijo/+yZ5Thr22+MHsTgzpM0b+E1MV7iMpaw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mZHuoHLbT9UfulklJm5eGg8Q0ICcRozi6Sd0qXfjBYYoGOIAbBR1+gw3Fgmm11TmZO3wCKdyF77eVEEc5V1w/WOKJrP3V2T1G6tMshOKrtgIqvGqfj6snanZP6/H8SOPQ+wKlFjFQAIRRwelW03iIQwlrkPBns17S+FcG6k35jM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=byKryE9L; 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="byKryE9L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11AC21F00A3A; Wed, 2 Sep 2026 17:00:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788368463; bh=21zjI9Xcw32ih4YadF8IlNWvz6bQgsRvY/kqV5dVaMA=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=byKryE9Lv5s3K+JQGJImtjfD0byGnvsScT87swdhpJeCwEPWHG+owbO+qreV2oMQq 4StXz9oJXoTMiM0g2daA4nVTRZFaC+1gJ6a2ZRFb7amP30a7Ta2uBGTqXK11tujQgn whuBbEpxT+A22/Tvbics4ozFKBw28z0t7Cd4mQ6cbq+fzpMhPl87TpLFzQV4CFkKut URsVju/ZM4vZyGFjLu4YRxSeyA2deg6ZSakhk+aKZ/QMiVsaEZVZbQAczjFaUExjNa NTqepT8RK/JQeDTHQyqksTP5r4jCOmmTiyGYdcJEcnSJwLJSyASUCg7/BTS0m65g+r f+cXQcDlwN4Pw== Date: Wed, 2 Sep 2026 18:00:55 +0100 From: "Lorenzo Stoakes (ARM)" To: Johannes Weiner Cc: Nimrod Oren , Andrew Morton , David Hildenbrand , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Hugh Dickins , Nirmoy Das , Dragos Tatulea , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm: remove min_free_kbytes adjustment for THP Message-ID: References: <20260901190123.3511535-1-noren@nvidia.com> <20260902162323.GO3004@cmpxchg.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 Content-Disposition: inline In-Reply-To: <20260902162323.GO3004@cmpxchg.org> On Wed, Sep 02, 2026 at 12:23:23PM -0400, Johannes Weiner wrote: > Just to summarize my take from the subthread with Zi: the premise of > this patch is to roll the regression dice on every THP setup out there > because certain ARM configurations result in a questionable pageblock size. > > I'm not against carefully evaluating and testing out today's need for > set_recommended_min_free_kbytes() in real world examples. But this is > not that. > > Nacked-by: Johannes Weiner Well you don't have to listen to me any more as ex-THP M ;) but my 2 pence... Isn't every possible change to address this kind of issue subject to exactly the same kind of constraint? I'd like to know what not rolling that dice looks like :) or what constitutes 'careful evaluation'. It feels like in certain areas we paint ourselves into a corner where everybody's too scared to change anything until we're sure nobody in the world is broken*. And so we continue to ride the merry-go-round of proposals/rejections indefinitely. All the while regressions in tip kernel are a regular occurrence (yes we don't want that, but they happen), and they are resolved as they arise. I wonder if we aren't limiting ourselves by thinking this way. Michal's proposal was that the original code was written _long_ before improvements in the compaction algorithm and fails to account for those. It seems odd to retain the same constraints given the rest of the kernel has changed. Perhaps a compromise would be to put the ability to disable this behind a config option or maybe a kernel arg? Of course that becomes something of a uAPI... but at least it gives the option to constrian this for those who want it. -- Cheers, Lorenzo * I think, for instance, about how the hell we can test changes to the compaction algorithm in a way that's sane and acceptable to people? Though that is something that really _does_ need it, as it's vastly more complicated and impactful than the proposed change here. I'm not sure what the answer is really :) ideally we'd have some vast farm of machines doing representative workloads with software that does careful statistically-signficant analysis of how they perform, but that seems rather like a pipe dream.