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Fri, 11 Nov 2022 17:40:54 -0800 (PST) Message-ID: Date: Sat, 12 Nov 2022 10:40:53 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.1 Subject: Re: Deprecating and removing SLOB Content-Language: en-US To: Conor Dooley , Vlastimil Babka Cc: Pasha Tatashin , Christoph Lameter , David Rientjes , Joonsoo Kim , Pekka Enberg , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Matthew Wilcox , Roman Gushchin , Linus Torvalds , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Catalin Marinas , Rustam Kovhaev , Andrew Morton , Josh Triplett , Arnd Bergmann , Russell King , Alexander Shiyan , Aaro Koskinen , Janusz Krzysztofik , Tony Lindgren , Yoshinori Sato , Rich Felker , Jonas Bonn , Stefan Kristiansson , Stafford Horne , "linux-arm-kernel@lists.infradead.org" , openrisc@lists.librecores.org, linux-riscv@lists.infradead.org, linux-sh@vger.kernel.org, Geert Uytterhoeven , Conor.Dooley@microchip.com, Paul Cercueil References: From: Damien Le Moal Organization: Western Digital Research In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668217264; a=rsa-sha256; cv=none; b=MJT/1kDm1vqYE4PvsQvtsOb53+MEFxIQJdgsJvzTvrlJtb+acfof62h12fnPW/0wLgFTcL xXAeP26tBVbtdIh7gTebMsHbLpxQzjfDPspb//s4r4Gdck+58NKydxrPUuHfcPhumWUSt7 t4xx9+Jg+XtOZjTjUEbIoqZBJl713J8= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=none ("invalid DKIM record") header.d=wdc.com header.s=dkim.wdc.com header.b=ScenQSV7; dkim=pass header.d=opensource.wdc.com header.s=dkim header.b=acKB5rby; dmarc=pass (policy=quarantine) header.from=opensource.wdc.com; spf=pass (imf14.hostedemail.com: domain of "prvs=308c9b51b=damien.lemoal@opensource.wdc.com" designates 216.71.154.42 as permitted sender) smtp.mailfrom="prvs=308c9b51b=damien.lemoal@opensource.wdc.com" ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668217264; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=zPJqZuv7toGDxxVKoInaied4TLhx4xsa8W/uWdIq2hc=; b=UdWcegoyHiKiSs8hqR+pgw8084+8kaX0l8nm3OPEhxXvDi+UrQ4fi6RzTB+fizRtx5kFud iNG2JqQs1wg5MWyv9xNh/tFGQiRiibnzY7T0JBcFxeCv8a+yGPkrBMEqDlma1RRXAkMl3+ 6uN1j4eqrevIbbVRTSRMRtwylpVAQps= X-Rspam-User: X-Stat-Signature: rf4s3339c3ku3du5h9oujq1fakr31sq1 X-Rspamd-Queue-Id: 3B493100004 Authentication-Results: imf14.hostedemail.com; dkim=none ("invalid DKIM record") header.d=wdc.com header.s=dkim.wdc.com header.b=ScenQSV7; dkim=pass header.d=opensource.wdc.com header.s=dkim header.b=acKB5rby; dmarc=pass (policy=quarantine) header.from=opensource.wdc.com; spf=pass (imf14.hostedemail.com: domain of "prvs=308c9b51b=damien.lemoal@opensource.wdc.com" designates 216.71.154.42 as permitted sender) smtp.mailfrom="prvs=308c9b51b=damien.lemoal@opensource.wdc.com" X-Rspamd-Server: rspam03 X-HE-Tag: 1668217263-70271 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: On 11/12/22 05:46, Conor Dooley wrote: > On Fri, Nov 11, 2022 at 11:33:30AM +0100, Vlastimil Babka wrote: >> On 11/8/22 22:44, Pasha Tatashin wrote: >>> On Tue, Nov 8, 2022 at 10:55 AM Vlastimil Babka wrote: >>>> >>>> Hi, >>>> >>>> as we all know, we currently have three slab allocators. As we discussed >>>> at LPC [1], it is my hope that one of these allocators has a future, and >>>> two of them do not. >>>> >>>> The unsurprising reasons include code maintenance burden, other features >>>> compatible with only a subset of allocators (or more effort spent on the >>>> features), blocking API improvements (more on that below), and my >>>> inability to pronounce SLAB and SLUB in a properly distinguishable way, >>>> without resorting to spelling out the letters. >>>> >>>> I think (but may be proven wrong) that SLOB is the easier target of the >>>> two to be removed, so I'd like to focus on it first. >>>> >>>> I believe SLOB can be removed because: >>>> >>>> - AFAIK nobody really uses it? It strives for minimal memory footprint >>>> by putting all objects together, which has its CPU performance costs >>>> (locking, lack of percpu caching, searching for free space...). I'm not >>>> aware of any "tiny linux" deployment that opts for this. For example, >>>> OpenWRT seems to use SLUB and the devices these days have e.g. 128MB >>>> RAM, not up to 16 MB anymore. I've heard anecdotes that the performance >>>> SLOB impact is too much for those who tried. Googling for >>>> "CONFIG_SLOB=y" yielded nothing useful. >>> >>> I am all for removing SLOB. >>> >>> There are some devices with configs where SLOB is enabled by default. >>> Perhaps, the owners/maintainers of those devices/configs should be >>> included into this thread: >>> >>> tatashin@soleen:~/x/linux$ git grep SLOB=y > >>> arch/riscv/configs/nommu_k210_defconfig:CONFIG_SLOB=y >>> arch/riscv/configs/nommu_k210_sdcard_defconfig:CONFIG_SLOB=y >>> arch/riscv/configs/nommu_virt_defconfig:CONFIG_SLOB=y > >> >> Turns out that since SLOB depends on EXPERT, many of those lack it so >> running make defconfig ends up with SLUB anyway, unless I miss something. >> Only a subset has both SLOB and EXPERT: >> >>> git grep CONFIG_EXPERT `git grep -l "CONFIG_SLOB=y"` > >> arch/riscv/configs/nommu_virt_defconfig:CONFIG_EXPERT=y > > I suppose there's not really a concern with the virt defconfig, but I > did check the output of `make nommu_k210_defconfig" and despite not > having expert it seems to end up CONFIG_SLOB=y in the generated .config. > > I do have a board with a k210 so I checked with s/SLOB/SLUB and it still > boots etc, but I have no workloads or w/e to run on it. I will try with SLUB over the weekend. -- Damien Le Moal Western Digital Research