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 X-Spam-Level: X-Spam-Status: No, score=-14.6 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B7950C433DF for ; Sat, 18 Jul 2020 02:29:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7D46A2073E for ; Sat, 18 Jul 2020 02:29:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="DWhiCCM1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728097AbgGRC3I (ORCPT ); Fri, 17 Jul 2020 22:29:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42066 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726817AbgGRC3I (ORCPT ); Fri, 17 Jul 2020 22:29:08 -0400 Received: from mail-lj1-x241.google.com (mail-lj1-x241.google.com [IPv6:2a00:1450:4864:20::241]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A905C0619D3 for ; Fri, 17 Jul 2020 19:23:41 -0700 (PDT) Received: by mail-lj1-x241.google.com with SMTP id z24so14783696ljn.8 for ; Fri, 17 Jul 2020 19:23:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=XBucRQmCckIgxAe4iGxrOI2VlPNSVQ5MjS//BrXowl8=; b=DWhiCCM1mnXVLmZLPyQ6TLmp/Q0ghflV02R2+vtAPtIA9LTV1RJ/nGkyLkaJZ5gA9V Uav/qtwiDBMDpFHPsoRNhgkPswShxw45BV+DcbcuqvpqiD8+Rgf4pLKyWx9Lu1ndRk13 Gq/HcKMLOEHfAKSQX4N86VOIRwMqK0j5A/GgsoA1IVFJr/t1CBb0/uBMzpr2ZAkY0NhS emzBdjCgZCI/FASzk4k50h5DIg2LRqG5EydbN/wkcN8vzJ19o9B2bHx8mS2HDJNP3L5K D+hf/SVmLT7OFsSDNO/asNRcLi6ErqXNOcIm46+yfkkaI/tmfFeeLhcjDj6/nbpbBuZr RkIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=XBucRQmCckIgxAe4iGxrOI2VlPNSVQ5MjS//BrXowl8=; b=ZYbuvrr/bKO5WlKDM+/xISPw1zk8BAqY5dHmLzmivy1b/BCnkuVeNOzGJ2/d/EGFut 7yRSaSi9poo0KxV0T9elU+F7BwG8URNlb2f594anMIzcX+1e9cMQ5DZ2rBFVQh3XG4J/ mb8pnmjJQhsTv+ghWboKRjG+SLxG3fx79NTsfu15S95EJSoxxoEKE2uB0nWzNDyxrukH QF4iRoDd57FQKlP/ZXFqZDwS7ZPWxGVeeCVcUeVe33RD7EtbF6iz7jfp4FjIzXNG4psN vkspHdtGE3KtkyJzmDscP6uCCfDx+dnrgFx0SDAx5aUYMcuy+oZjC9WyUsu6lUuQIl4G dAKw== X-Gm-Message-State: AOAM5337kmC3PtiK3qfWjEUgtpW0b20GVvtgXQueyeTckBFLLkk9FLW5 JZ7d/qfOasdUugyM59CjCFlmlqDNIepQAlKzNooJcQ== X-Google-Smtp-Source: ABdhPJxFG8TTBZ82BF8vGQkuEhRSdSEt3eb+PZCn0Nq6rXD0Z3WCgnNAvZRbIyXi2wJ4me/K4jteUFrv80+ubMuZ4is= X-Received: by 2002:a2e:9907:: with SMTP id v7mr5743009lji.347.1595039019412; Fri, 17 Jul 2020 19:23:39 -0700 (PDT) MIME-Version: 1.0 References: <20200717162403.26170-1-sjpark@amazon.com> In-Reply-To: <20200717162403.26170-1-sjpark@amazon.com> From: Shakeel Butt Date: Fri, 17 Jul 2020 19:23:28 -0700 Message-ID: Subject: Re: Re: Re: [PATCH v18 06/14] mm/damon: Implement callbacks for the virtual memory address spaces To: SeongJae Park Cc: Andrew Morton , SeongJae Park , Jonathan.Cameron@huawei.com, Andrea Arcangeli , acme@kernel.org, alexander.shishkin@linux.intel.com, amit@kernel.org, benh@kernel.crashing.org, brendan.d.gregg@gmail.com, Brendan Higgins , Qian Cai , Colin Ian King , Jonathan Corbet , David Hildenbrand , dwmw@amazon.com, foersleo@amazon.de, Ian Rogers , jolsa@redhat.com, "Kirill A. Shutemov" , mark.rutland@arm.com, Mel Gorman , Minchan Kim , Ingo Molnar , namhyung@kernel.org, "Peter Zijlstra (Intel)" , Randy Dunlap , Rik van Riel , David Rientjes , Steven Rostedt , rppt@kernel.org, sblbir@amazon.com, shuah@kernel.org, sj38.park@gmail.com, snu@amazon.de, Vlastimil Babka , Vladimir Davydov , Yang Shi , Huang Ying , linux-damon@amazon.com, Linux MM , linux-doc@vger.kernel.org, LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Fri, Jul 17, 2020 at 9:24 AM SeongJae Park wrote: > > 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. > > Hmm, I will think more about it. Somehow I feel if we want to monitor at the page sized region granularity then this will be really helpful. Anyways, it needs more brainstorming. BTW I am still going over the series and my humble request would be to wait till I have gone through the series completely and provided the feedback then you can send the next version after incorporating the feedback. Shakeel