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]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEA79C04FFE for ; Wed, 8 May 2024 09:02:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 65D726B008C; Wed, 8 May 2024 05:02:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 60DFB6B0098; Wed, 8 May 2024 05:02:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4D6716B009B; Wed, 8 May 2024 05:02:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 319016B008C for ; Wed, 8 May 2024 05:02:48 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id C1C29C1447 for ; 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s=arc-20220608; d=hostedemail.com; t=1715158966; a=rsa-sha256; cv=none; b=WkzZTQLlKfzBCwZ6ohE6aeRYSGTfP2sQxbldoSK2dNvFxphCsPsza345vHVitaJoX1mhhN sG1Hu51+AL53EPsnVOWh5LMRVuddExG3ILOz0B6FR/L3Y6cNr/31jab1/DDMgMZRXo3QBC 7eAvFlwrxWk8llbCdCmb1IaEL/f0aaI= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=none; spf=pass (imf01.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9ECFD1063; Wed, 8 May 2024 02:03:10 -0700 (PDT) Received: from [10.57.67.194] (unknown [10.57.67.194]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 43F0C3F6A8; Wed, 8 May 2024 02:02:43 -0700 (PDT) Message-ID: Date: Wed, 8 May 2024 10:02:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/8] mm: shmem: add multi-size THP sysfs interface for anonymous shmem Content-Language: en-GB To: David Hildenbrand , Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com, shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <6b4afed1ef26dbd08ae9ec58449b329564dcef3e.1714978902.git.baolin.wang@linux.alibaba.com> <30329a82-45b9-4e78-8c48-bd56af113786@arm.com> <0b3735bc-2ad7-44f8-808b-37fc90d57199@linux.alibaba.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: atqxw3geanrx3cyaeyox3qforu191da3 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D7F704001E X-HE-Tag: 1715158965-639141 X-HE-Meta: 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 kwmTv9Jo m0rhOg7RuEZmR5M5R9g7qEZC2KI/Q3YabCzc2iSYxPz65tjdELn26pSVs+z9pf0Oj8iWfsPFYg779aNq0zYcrdbUmu8VlrF5+arG4XhZ2wFsnX4N651FXGDQ53CpD7aQuKFfZ/u9h0UUT6Fr72APPm6DwWWOtOIeZ/1/Uzgq0b/tObgrk61lH7+rlBD8zckxgTY6z0wUurKpMY8WK3/OsQnp+ty3Cn7v080Ky 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 08/05/2024 08:12, David Hildenbrand wrote: > On 08.05.24 09:08, David Hildenbrand wrote: >> On 08.05.24 06:45, Baolin Wang wrote: >>> >>> >>> On 2024/5/7 18:52, Ryan Roberts wrote: >>>> On 06/05/2024 09:46, Baolin Wang wrote: >>>>> To support the use of mTHP with anonymous shmem, add a new sysfs interface >>>>> 'shmem_enabled' in the '/sys/kernel/mm/transparent_hugepage/hugepages-kB/' >>>>> directory for each mTHP to control whether shmem is enabled for that mTHP, >>>>> with a value similar to the top level 'shmem_enabled', which can be set to: >>>>> "always", "inherit (to inherit the top level setting)", "within_size", >>>>> "advise", >>>>> "never", "deny", "force". These values follow the same semantics as the top >>>>> level, except the 'deny' is equivalent to 'never', and 'force' is equivalent >>>>> to 'always' to keep compatibility. >>>> >>>> We decided at [1] to not allow 'force' for non-PMD-sizes. >>>> >>>> [1] >>>> https://lore.kernel.org/linux-mm/533f37e9-81bf-4fa2-9b72-12cdcb1edb3f@redhat.com/ >>>> >>>> However, thinking about this a bit more, I wonder if the decision we made to >>>> allow all hugepages-xxkB/enabled controls to take "inherit" was the wrong one. >>>> Perhaps we should have only allowed the PMD-sized enable=inherit (this is just >>>> for legacy back compat after all, I don't think there is any use case where >>>> changing multiple mTHP size controls atomically is actually useful). Applying >>> >>> Agree. This is also our usage of 'inherit'. > > Missed that one: there might be use cases in the future once we would start > defaulting to "inherit" for all knobs (a distro might default to that) and > default-enable THP in the global knob. Then, it would be easy to disable any THP > by disabling the global knob. (I think that's the future we're heading to, where > we'd have an "auto" mode that can be set on the global toggle). > > But I am just making up use cases ;) I think it will be valuable and just doing > it consistently now might be cleaner. I agree that consistency between enabled and shmem_enabled is top priority. And yes, I had forgotten about the glorious "auto" future. So probably continuing all sizes to select "inherit" is best. But for shmem_enabled, that means we need the following error checking: - It is an error to set "force" for any size except PMD-size - It is an error to set "force" for the global control if any size except PMD- size is set to "inherit" - It is an error to set "inherit" for any size except PMD-size if the global control is set to "force". Certainly not too difficult to code and prove to be correct, but not the nicest UX from the user's point of view when they start seeing errors. I think we previously said this would likely be temporary, and if/when tmpfs gets mTHP support, we could simplify and allow all sizes to be set to "force". But I wonder if tmpfs would ever need explicit mTHP control? Maybe it would be more suited to the approach the page cache takes to transparently ramp up the folio size as it faults more in. (Just saying there is a chance that this error checking becomes permanent).