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 C8778C7EE2E for ; Wed, 24 May 2023 15:32:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 35563900002; Wed, 24 May 2023 11:32:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1F4FB900007; Wed, 24 May 2023 11:32:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F37F1900002; Wed, 24 May 2023 11:32:56 -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 DC07A900007 for ; Wed, 24 May 2023 11:32:56 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id A6A87C09F4 for ; Wed, 24 May 2023 15:32:56 +0000 (UTC) X-FDA: 80825541552.24.49B53B6 Received: from mail-qk1-f182.google.com (mail-qk1-f182.google.com [209.85.222.182]) by imf28.hostedemail.com (Postfix) with ESMTP id BEDCBC0014 for ; Wed, 24 May 2023 15:32:53 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=joelfernandes.org header.s=google header.b=On7I5ayO; dmarc=none; spf=pass (imf28.hostedemail.com: domain of joel@joelfernandes.org designates 209.85.222.182 as permitted sender) smtp.mailfrom=joel@joelfernandes.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1684942373; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=TYAWyrxgPtqWXYxm6cJhdFwBx5wHciPZ/aYd0labdNY=; b=BMMGGCrlORCilfn/NP1v3qTPlgbAkieCL+tyD+zVggqEVIUQ8ILu3Jya64zcAAmE+8KETt bcJMEIt/QQVLSZiC+otvhwc/T+D26f1PTR3NMQu3oe4NLA1nw3D1rI26DbTqzPCBIISXQs PCdzXZ7XEgIbBxiL7dOD/p/7nLxnFWQ= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=joelfernandes.org header.s=google header.b=On7I5ayO; dmarc=none; spf=pass (imf28.hostedemail.com: domain of joel@joelfernandes.org designates 209.85.222.182 as permitted sender) smtp.mailfrom=joel@joelfernandes.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1684942373; a=rsa-sha256; cv=none; b=Qt3UnNg62YzkUG/IxKac9TMc2lf4xKUgY4+zFsZoIdwIJ87pnQZM4Iun/wzJlBurVHxqMQ gcpAJJspSfMyVQC/TW97IrCAStWT5VIqNreBMgcS/dQNLII+HUjuYdCOTG4rAG2VnaRuBb rAQ2Xey7ztMV9sZj9wliiiVGYOi5LLI= Received: by mail-qk1-f182.google.com with SMTP id af79cd13be357-75b04e897a5so152586185a.2 for ; Wed, 24 May 2023 08:32:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; t=1684942372; x=1687534372; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=TYAWyrxgPtqWXYxm6cJhdFwBx5wHciPZ/aYd0labdNY=; b=On7I5ayOaYhi5YG/GPdB9nxaPm77pHmMCGllRGYcQUbOR9RaWe8+E1kwIyz/Gm1IO2 lzlpVKQhkPTjP/JCXbURVFFWQ3jgbHYHGgepr9uzBOnTK1CeaL3pkQv0Y3ntC9d96Fw5 Q/V2PreQmRTT8rUh3sL+unZfL9jgCw+Ofoan0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1684942372; x=1687534372; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=TYAWyrxgPtqWXYxm6cJhdFwBx5wHciPZ/aYd0labdNY=; b=EtlN3cxPZO68aiK9+5XrhgFJHa/ZaesndaV+MDR/n+XfgNtPzs7Pqmvu6GUqS6IDg/ b3qYP4FeaSLKftnYwvoXArLWUNGq3oVVuPfQklmLZrqWMTNVHVJJ1Xuwi/CpQA4G9c6V YZCQBP1tuYHAiMm2JsPjf2tS4rQVoSYjbaWJyPYD9Uhbsk23DSRBMWiGW2zyG3SfQ4B5 RSPNMLHQQITIm8tolj0an5mork8H2GwDMGi0KNnSVYbjGky0vkukifxgJvz2Dm4AL3CL IKtywCgzmWXZgbwSVOyXTLgOIY8ZB0FUzR4nEPBGvTVk2Fo+Numv7HxL8GVSKyRgCnj2 6C4g== X-Gm-Message-State: AC+VfDyJAFi+yJ5JasTzgCqCWVFXieEIQSWrMQ6v+9Jgp1Orp1KmhiNh QKgVs+BJ+dLP3hgqv0Sffx82bA== X-Google-Smtp-Source: ACHHUZ5whL3pswyeHoY7J7ITOmoL7n/+ckLUp2U8dIz21/Y207+W8uQinoe+VqHo2CMLKpf+5MBPGQ== X-Received: by 2002:a05:620a:172a:b0:75b:23a1:3634 with SMTP id az42-20020a05620a172a00b0075b23a13634mr9248078qkb.69.1684942372538; Wed, 24 May 2023 08:32:52 -0700 (PDT) Received: from joelboxx.c.googlers.com.com (129.239.188.35.bc.googleusercontent.com. [35.188.239.129]) by smtp.gmail.com with ESMTPSA id v18-20020a05620a123200b007590aa4b115sm3296906qkj.87.2023.05.24.08.32.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 May 2023 08:32:51 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" , Linus Torvalds , linux-kselftest@vger.kernel.org, linux-mm@kvack.org, Shuah Khan , Vlastimil Babka , Michal Hocko , Lorenzo Stoakes , Kirill A Shutemov , "Liam R. Howlett" , "Paul E. McKenney" , Suren Baghdasaryan , Kalesh Singh , Lokesh Gidra Subject: [PATCH v3 1/6] mm/mremap: Optimize the start addresses in move_page_tables() Date: Wed, 24 May 2023 15:32:34 +0000 Message-ID: <20230524153239.3036507-2-joel@joelfernandes.org> X-Mailer: git-send-email 2.40.1.698.g37aff9b760-goog In-Reply-To: <20230524153239.3036507-1-joel@joelfernandes.org> References: <20230524153239.3036507-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: BEDCBC0014 X-Stat-Signature: tatcmqcuepi73bpkacyegzzzdk1hkt45 X-HE-Tag: 1684942373-925510 X-HE-Meta: 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 fQga1gJf 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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: Recently, we see reports [1] of a warning that triggers due to move_page_tables() doing a downward and overlapping move on a mutually-aligned offset within a PMD. By mutual alignment, I mean the source and destination addresses of the mremap are at the same offset within a PMD. This mutual alignment along with the fact that the move is downward is sufficient to cause a warning related to having an allocated PMD that does not have PTEs in it. This warning will only trigger when there is mutual alignment in the move operation. A solution, as suggested by Linus Torvalds [2], is to initiate the copy process at the PMD level whenever such alignment is present. Implementing this approach will not only prevent the warning from being triggered, but it will also optimize the operation as this method should enhance the speed of the copy process whenever there's a possibility to start copying at the PMD level. Some more points: a. The optimization can be done only when both the source and destination of the mremap do not have anything mapped below it up to a PMD boundary. I add support to detect that. b. #1 is not a problem for the call to move_page_tables() from exec.c as nothing is expected to be mapped below the source. However, for non-overlapping mutually aligned moves as triggered by mremap(2), I added support for checking such cases. c. I currently only optimize for PMD moves, in the future I/we can build on this work and do PUD moves as well if there is a need for this. But I want to take it one step at a time. d. We need to be careful about mremap of ranges within the VMA itself. For this purpose, I added checks to determine if the address after alignment falls within its VMA itself. [1] https://lore.kernel.org/all/ZB2GTBD%2FLWTrkOiO@dhcp22.suse.cz/ [2] https://lore.kernel.org/all/CAHk-=whd7msp8reJPfeGNyt0LiySMT0egExx3TVZSX3Ok6X=9g@mail.gmail.com/ Suggested-by: Linus Torvalds Signed-off-by: Joel Fernandes (Google) --- mm/mremap.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+) diff --git a/mm/mremap.c b/mm/mremap.c index 411a85682b58..184d52f83b19 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -478,6 +478,53 @@ static bool move_pgt_entry(enum pgt_entry entry, struct vm_area_struct *vma, return moved; } +/* + * A helper to check if a previous mapping exists. Required for + * move_page_tables() and realign_addr() to determine if a previous mapping + * exists before we can do realignment optimizations. + */ +static bool can_align_down(struct vm_area_struct *vma, unsigned long addr_to_align, + unsigned long mask) +{ + unsigned long addr_masked = addr_to_align & mask; + struct vm_area_struct *prev = NULL, *cur = NULL; + + /* If the masked address is within vma, we cannot align the address down. */ + if (vma->vm_start <= addr_masked) + return false; + + /* + * Attempt to find VMA before prev that contains the address. + * On any issue finding prev, assume there is a mapping and return false + * which will turn off any optimizations. Yes, we're conservative! + * The mmap write lock is held here, so the lookup is safe. + */ + cur = find_vma_prev(vma->vm_mm, vma->vm_start, &prev); + if (!cur || cur != vma || !prev) + return false; + + /* The masked address fell within some previous mapping. */ + if (prev->vm_end > addr_masked) + return false; + + return true; +} + +/* Opportunistically realign to specified boundary for faster copy. */ +static void realign_addr(unsigned long *old_addr, struct vm_area_struct *old_vma, + unsigned long *new_addr, struct vm_area_struct *new_vma, + unsigned long mask) +{ + bool mutually_aligned = (*old_addr & ~mask) == (*new_addr & ~mask); + + if ((*old_addr & ~mask) && mutually_aligned + && can_align_down(old_vma, *old_addr, mask) + && can_align_down(new_vma, *new_addr, mask)) { + *old_addr = *old_addr & mask; + *new_addr = *new_addr & mask; + } +} + unsigned long move_page_tables(struct vm_area_struct *vma, unsigned long old_addr, struct vm_area_struct *new_vma, unsigned long new_addr, unsigned long len, @@ -493,6 +540,15 @@ unsigned long move_page_tables(struct vm_area_struct *vma, old_end = old_addr + len; + /* + * If possible, realign addresses to PMD boundary for faster copy. + * Don't align for intra-VMA moves as we may destroy existing mappings. + */ + if ((vma != new_vma) + && (len >= PMD_SIZE - (old_addr & ~PMD_MASK))) { + realign_addr(&old_addr, vma, &new_addr, new_vma, PMD_MASK); + } + if (is_vm_hugetlb_page(vma)) return move_hugetlb_page_tables(vma, new_vma, old_addr, new_addr, len); @@ -565,6 +621,13 @@ unsigned long move_page_tables(struct vm_area_struct *vma, mmu_notifier_invalidate_range_end(&range); + /* + * Prevent negative return values when {old,new}_addr was realigned + * but we broke out of the above loop for the first PMD itself. + */ + if (len + old_addr < old_end) + return 0; + return len + old_addr - old_end; /* how much done */ } -- 2.40.1.698.g37aff9b760-goog