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Mon, 15 Dec 2025 18:23:09 -0800 (PST) Message-ID: <09d2d256-2eba-41ea-a397-dca4df5d5a2a@kernel.dk> Date: Mon, 15 Dec 2025 19:23:07 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: retiring laptop_mode? was Re: [PATCH] mm: vmscan: always allow writeback during memcg reclaim To: Johannes Weiner , Christoph Hellwig Cc: Deepanshu Kartikey , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org References: <20251213083639.364539-1-kartikey406@gmail.com> <20251215041200.GB905277@cmpxchg.org> <20251215200838.GC905277@cmpxchg.org> Content-Language: en-US From: Jens Axboe In-Reply-To: <20251215200838.GC905277@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: bcq73ctzxyxjgxhfg783m5fex76erprf X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 3A88D1C000E X-Rspam-User: X-HE-Tag: 1765851791-510213 X-HE-Meta: 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 Y3Bpb16/ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/15/25 1:08 PM, Johannes Weiner wrote: > On Sun, Dec 14, 2025 at 10:59:11PM -0800, Christoph Hellwig wrote: >> On Sun, Dec 14, 2025 at 11:12:00PM -0500, Johannes Weiner wrote: >>> That reasoning doesn't make sense to me. Reclaim is always in response >>> to an allocation need. The laptop_mode idea applies to cgroup reclaim >>> as much as any other reclaim. >>> >>> Now obviously all of this is pretty dated. Reclaim doesn't do >>> filesystem writes anymore, and I'm not sure there are a whole lot of >>> laptops with rotational drives left, either. Also I doubt anybody is >>> still using zone_reclaim_mode (which is where the may_unmap is from). >> >> Yeah. I wonder if we should retire laptop_mode. It was a cute hack >> back then, but it has it's ugly fingers in way to many places and >> should be mostly obsolete by how writeback works these days. > > Yes, that makes sense to me. How about the below? > > It doesn't actually get rid of the reclaim toggles - I added comments > for the other usecases. But it's a nice diffstat nonetheless. > > Debated whether to add some sort of deprecation sysctl handler, but at > least systemd-sysctl just prints a warning and still applies other > settings from the same config file. > > --- > > From 868f67e9d0d4465a6c22d8a147084944e7569c8d Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Mon, 15 Dec 2025 12:57:53 -0500 > Subject: [PATCH] mm/block/fs: remove laptop_mode > > Laptop mode was introduced to save battery, by delaying and > consolidating writes and maximize the time rotating hard drives > wouldn't have to spin. Needless to say, this is a scenario of the > (in)glorious past. > > The footprint of the feature is small, but nevertheless it's a > complicating factor in mm, block, filesystems. Developers don't think > about it, and the decision-making in reclaim looks dubious. It likely > hasn't been tested in years while the surrounding code has evolved. >From a quick glance, looks good to me: Acked-by: Jens Axboe -- Jens Axboe