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 414DDCD128A for ; Mon, 8 Apr 2024 10:39:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 629366B0085; Mon, 8 Apr 2024 06:39:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5D8FF6B0087; Mon, 8 Apr 2024 06:39:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4C6D16B0088; Mon, 8 Apr 2024 06:39:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 34C306B0085 for ; Mon, 8 Apr 2024 06:39:56 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id B599E1C0286 for ; Mon, 8 Apr 2024 10:39:55 +0000 (UTC) X-FDA: 81986019150.16.FD9417C Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf20.hostedemail.com (Postfix) with ESMTP id A270B1C000F for ; Mon, 8 Apr 2024 10:39:53 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf20.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1712572794; 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; bh=/UAVlOfw12QoCZS/26M3nRaUPDrQJICILLNc/4HVigM=; b=WbqqOT2jVbXGnwd9BPDc4c70XnBW14KU/dGBDn8rlERmZHcRLDi9xT9mbd0BHj089vST53 Hcimm+xnoGWV2pLg93bdTKjBCEXlJsE107AVZayTIfa0Bmk8Kt36E2jvZ8uGHSDX17Y0it 2n/5Y696SqGOTX6HbTBST7KbblxuuGU= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf20.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1712572794; a=rsa-sha256; cv=none; b=lPqNtmaIuC+LVeTiMuDN6yUVEj5At/avApEexHzvQdpFPZIkPv6ivbCV7CNl7xfyyc9PrJ s5COQ77QzeqwGWyCxfm6ZorF9GNqW8NeCITnJ85lqZtySKL3wK9JtquI7JvjQcfK8Am5m2 fSNeLvxm7yx9VlNXQJFy+QEZXVNGrlo= 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 2031F339; Mon, 8 Apr 2024 03:40:23 -0700 (PDT) Received: from [10.57.73.169] (unknown [10.57.73.169]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AA9FC3F766; Mon, 8 Apr 2024 03:39:50 -0700 (PDT) Message-ID: Date: Mon, 8 Apr 2024 11:39:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/6] mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache() Content-Language: en-GB To: David Hildenbrand , Andrew Morton , Matthew Wilcox , Huang Ying , Gao Xiang , Yu Zhao , Yang Shi , Michal Hocko , Kefeng Wang , Barry Song <21cnbao@gmail.com>, Chris Li , Lance Yang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240403114032.1162100-1-ryan.roberts@arm.com> <20240403114032.1162100-3-ryan.roberts@arm.com> <051052af-3b56-4290-98d3-fd5a1eb11ce1@redhat.com> <73adae65-4429-41d7-bbb6-4c58156060d3@arm.com> <7d3d3c58-1bb1-4d70-9ae3-fa96f6d624d8@redhat.com> <79c5513b-b3f2-4fbb-a3c7-a09894d54d22@redhat.com> From: Ryan Roberts In-Reply-To: <79c5513b-b3f2-4fbb-a3c7-a09894d54d22@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: A270B1C000F X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 38dokd8mgq3p7gpyjarrsur18jjjns6i X-HE-Tag: 1712572793-213788 X-HE-Meta: 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 tfhu5QFg +79yQJ8BZIL2+I6VyRhm6SGoQymptelHjMJ6coULSSv22NbG4JD/4w+zBdGmnd+E4cnZRkggBtuw8kRt/ouG7nMRzzbZ2vYfLhLYCAj8Uz8eeeMxfOYT/L/f97KJ564O9XWBaMVYmVRXVbvKOv7YFueobQWFl8o9uEjDYIelivRg2aqns6/IOwh7guA3LmG8ab8cm 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 08/04/2024 11:24, David Hildenbrand wrote: > On 08.04.24 12:07, Ryan Roberts wrote: >> On 08/04/2024 10:43, David Hildenbrand wrote: >>> >>>>>> + >>>>>> +/** >>>>>> + * swap_pte_batch - detect a PTE batch for a set of contiguous swap entries >>>>>> + * @start_ptep: Page table pointer for the first entry. >>>>>> + * @max_nr: The maximum number of table entries to consider. >>>>>> + * @entry: Swap entry recovered from the first table entry. >>>>>> + * >>>>>> + * Detect a batch of contiguous swap entries: consecutive (non-present) PTEs >>>>>> + * containing swap entries all with consecutive offsets and targeting the >>>>>> same >>>>>> + * swap type. >>>>>> + * >>>>> >>>>> Likely you should document that any swp pte bits are ignored? () >>>> >>>> Sorry I don't understand this comment. I thought any non-none, non-present PTE >>>> was always considered to contain only a "swap entry" and a swap entry consists >>>> of a "type" and an "offset" only. (and its a special "non-swap" swap entry if >>>> type > SOME_CONSTANT) Are you saying there are additional fields in the PTE >>>> that >>>> are not part of the swap entry? >>> >>> >>> pte_swp_soft_dirty() >>> pte_swp_clear_exclusive() >>> pte_swp_uffd_wp() >>> >>> Are PTE bits used for swp PTE. >> >> Ahh wow. mind blown. Looks like a massive hack... why not store them in the >> arch-independent swap entry, rather than have them squat independently in the >> PTE? > > I think that was discussed at some point, but it not only requires quite some > churn to change it (all that swp entry code is a mess), these bits are > conceptually really per PTE and not something you would want to pass into actual > swap handling code that couldn't care less about all of these. > > I looked at this when I added SWP exclusive, but accidentally losing the SWP > exclusive marker when converting back and forth made me go the PTE route instead. > > Then, the available PTE bits are a bit scattered on some architectures, and > converting entry<->PTE gets even uglier if we don't want to "lose" available bits. > > Probably the whole "unsigned long swp_entry" stuff should be replaced by a > proper struct where we could more easily add flags and have the arch code handle > the conversion to the PTE just once. The arch-specific swp_entry stuff is > another nasty thing IMHO. Yep understood. I'll file this under "there be dragons". Thanks for the explanation. > >> >> OK, my implementation is buggy. I'll re-spin to fix this. >> >> >>> >>> There is also dirty/young for migration entries, but that's not of a concern >>> here, because we stop for non_swap_entry(). >> >> Looks like these are part of the offset field in the arch-independent swap entry >> - much cleaner ;-). > > Note that it only applies to migration entries, and only when we have some spare > bits due to PFN < offset. Yep got it. Thanks!