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[23.128.96.18]) by mx.google.com with ESMTP id n27si5567359eje.543.2020.07.17.09.26.54; Fri, 17 Jul 2020 09:27:18 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@amazon.com header.s=amazon201209 header.b="HtlLfLg/"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=amazon.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726359AbgGQQYy (ORCPT + 99 others); Fri, 17 Jul 2020 12:24:54 -0400 Received: from smtp-fw-4101.amazon.com ([72.21.198.25]:40900 "EHLO smtp-fw-4101.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726013AbgGQQYy (ORCPT ); Fri, 17 Jul 2020 12:24:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1595003092; x=1626539092; h=from:to:cc:subject:date:message-id:in-reply-to: mime-version; bh=RHrkZufRMjuhRrtp+fu64P8S022XMgDUnpDRw0BJDtw=; b=HtlLfLg/Mf6dXcS1cl5WN+bGLoYI5iiNxui2uLkCqpdzTEb80HIsOiZ3 cVKL/p8lViOOYNp05tIRGCT7TJyuYXHle6DFdm+BpR5uYI/L0UaHdv/Sq kF31rLgxYIL9vFoeXB33cGEL+Y1PWdgbOODWCfRmshL+vzdNFqVVU2ik/ M=; IronPort-SDR: jGCdmuiqviVKS7LNe01Af37ZHTXzusL6v2JeQsNwoZ2Ls0nTNd5naQLykLDp0fWbiRgLeFhu+K mYbNk+xaAAOQ== X-IronPort-AV: E=Sophos;i="5.75,362,1589241600"; d="scan'208";a="42609914" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-1d-37fd6b3d.us-east-1.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-4101.iad4.amazon.com with ESMTP; 17 Jul 2020 16:24:49 +0000 Received: from EX13MTAUEA002.ant.amazon.com (iad55-ws-svc-p15-lb9-vlan3.iad.amazon.com [10.40.159.166]) by email-inbound-relay-1d-37fd6b3d.us-east-1.amazon.com (Postfix) with ESMTPS id A7FE9282349; Fri, 17 Jul 2020 16:24:38 +0000 (UTC) Received: from EX13D31EUA004.ant.amazon.com (10.43.165.161) by EX13MTAUEA002.ant.amazon.com (10.43.61.77) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 17 Jul 2020 16:24:37 +0000 Received: from u886c93fd17d25d.ant.amazon.com (10.43.160.100) by EX13D31EUA004.ant.amazon.com (10.43.165.161) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 17 Jul 2020 16:24:21 +0000 From: SeongJae Park To: Shakeel Butt CC: SeongJae Park , Andrew Morton , SeongJae Park , , Andrea Arcangeli , , , , , , Brendan Higgins , Qian Cai , Colin Ian King , Jonathan Corbet , "David Hildenbrand" , , , Ian Rogers , , "Kirill A. Shutemov" , , Mel Gorman , Minchan Kim , Ingo Molnar , , "Peter Zijlstra (Intel)" , Randy Dunlap , Rik van Riel , David Rientjes , Steven Rostedt , , , , , , Vlastimil Babka , Vladimir Davydov , Yang Shi , Huang Ying , , Linux MM , , LKML Subject: Re: Re: Re: [PATCH v18 06/14] mm/damon: Implement callbacks for the virtual memory address spaces Date: Fri, 17 Jul 2020 18:24:03 +0200 Message-ID: <20200717162403.26170-1-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: (raw) MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.43.160.100] X-ClientProxiedBy: EX13D05UWB003.ant.amazon.com (10.43.161.26) To EX13D31EUA004.ant.amazon.com (10.43.165.161) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Jul 2020 08:17:09 -0700 Shakeel Butt wrote: > On Thu, Jul 16, 2020 at 11:54 PM SeongJae Park wrote: > > > > On Thu, 16 Jul 2020 17:46:54 -0700 Shakeel Butt wrote: > > > > > On Mon, Jul 13, 2020 at 1:44 AM SeongJae Park wrote: > > > > > > > > From: SeongJae Park > > > > > > > > This commit introduces a reference implementation of the address space > > > > specific low level primitives for the virtual address space, so that > > > > users of DAMON can easily monitor the data accesses on virtual address > > > > spaces of specific processes by simply configuring the implementation to > > > > be used by DAMON. > > > > > > > > The low level primitives for the fundamental access monitoring are > > > > defined in two parts: > > > > 1. Identification of the monitoring target address range for the address > > > > space. > > > > 2. Access check of specific address range in the target space. > > > > > > > > The reference implementation for the virtual address space provided by > > > > this commit is designed as below. > > > > > > > > PTE Accessed-bit Based Access Check > > > > ----------------------------------- > > > > > > > > The implementation uses PTE Accessed-bit for basic access checks. That > > > > is, it clears the bit for next sampling target page and checks whether > > > > it set again after one sampling period. To avoid disturbing other > > > > Accessed bit users such as the reclamation logic, the implementation > > > > adjusts the ``PG_Idle`` and ``PG_Young`` appropriately, as same to the > > > > 'Idle Page Tracking'. > > > > > > > > VMA-based Target Address Range Construction > > > > ------------------------------------------- > > > > > > > > Only small parts in the super-huge virtual address space of the > > > > processes are mapped to physical memory and accessed. Thus, tracking > > > > the unmapped address regions is just wasteful. However, because DAMON > > > > can deal with some level of noise using the adaptive regions adjustment > > > > mechanism, tracking every mapping is not strictly required but could > > > > even incur a high overhead in some cases. That said, too huge unmapped > > > > areas inside the monitoring target should be removed to not take the > > > > time for the adaptive mechanism. > > > > > > > > For the reason, this implementation converts the complex mappings to > > > > three distinct regions that cover every mapped area of the address > > > > space. Also, the two gaps between the three regions are the two biggest > > > > unmapped areas in the given address space. The two biggest unmapped > > > > areas would be the gap between the heap and the uppermost mmap()-ed > > > > region, and the gap between the lowermost mmap()-ed region and the stack > > > > in most of the cases. Because these gaps are exceptionally huge in > > > > usual address spacees, excluding these will be sufficient to make a > > > > reasonable trade-off. Below shows this in detail:: > > > > > > > > > > > > > > > > > > > > (small mmap()-ed regions and munmap()-ed regions) > > > > > > > > > > > > > > > > > > > > Signed-off-by: SeongJae Park > > > > Reviewed-by: Leonard Foerster > > > [snip] > > > > + > > > > +static void damon_mkold(struct mm_struct *mm, unsigned long addr) > > > > +{ > > > > + pte_t *pte = NULL; > > > > + pmd_t *pmd = NULL; > > > > + spinlock_t *ptl; > > > > + > > > > + if (follow_pte_pmd(mm, addr, NULL, &pte, &pmd, &ptl)) > > > > + return; > > > > + > > > > + if (pte) { > > > > + if (pte_young(*pte)) { > > > > > > Any reason for skipping mmu_notifier_clear_young()? Why exclude VMs as > > > DAMON's target applications? > > > > Obviously my mistake, thank you for pointing this! I will add the function > > call in the next spin. > > > > Similarly mmu_notifier_test_young() for the damon_young(). Yes, indeed. Thanks for pointing this, either :) > BTW I think we can combine ctx->prepare_access_checks() and > ctx->check_accesses() into one i.e. get the young state for the previous > cycle and mkold for the next cycle in a single step. Yes, we could. But, I'm unsure what is the advantage of doing that. First of all, if the combined implementation is required, peopld could simply implement the two logics in the combined way in one of the callbacks and leave the other one blank. Also, I'm worrying if combining those could make the code a little bit hard to read. IMHO, I think separating those makes the 'kdamond_fn()' code little bit easier to read. Actually, I started from the combined approach but separated the two logics since v7 after Jonathan's comment[1]. [1] https://lore.kernel.org/linux-mm/20200310085721.00000a0f@Huawei.com/ > > I am wondering if there is any advantage to having "Page Idle > Tracking" beside DAMON. I think we can make them mutually exclusive. > Once we have established that I think DAMON can steal the two page > flag bits from it and can make use of them. What do you think? Again, yes, I think we could. But I don't see clear advantage of it for now. Thanks, SeongJae Park