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From: Shakeel Butt <shakeelb@google.com>
To: SeongJae Park <sjpark@amazon.com>
Cc: Greg Thelen <gthelen@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	 SeongJae Park <sjpark@amazon.de>,
	Jonathan.Cameron@huawei.com,
	 Andrea Arcangeli <aarcange@redhat.com>,
	acme@kernel.org, alexander.shishkin@linux.intel.com,
	 amit@kernel.org, benh@kernel.crashing.org,
	brendan.d.gregg@gmail.com,
	 Brendan Higgins <brendanhiggins@google.com>,
	Qian Cai <cai@lca.pw>,  Colin Ian King <colin.king@canonical.com>,
	Jonathan Corbet <corbet@lwn.net>,
	 David Hildenbrand <david@redhat.com>,
	dwmw@amazon.com, foersleo@amazon.de,
	 Ian Rogers <irogers@google.com>,
	jolsa@redhat.com,  "Kirill A. Shutemov" <kirill@shutemov.name>,
	mark.rutland@arm.com, Mel Gorman <mgorman@suse.de>,
	 Minchan Kim <minchan@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	namhyung@kernel.org,
	 "Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	 Rik van Riel <riel@surriel.com>,
	David Rientjes <rientjes@google.com>,
	 Steven Rostedt <rostedt@goodmis.org>,
	rppt@kernel.org, sblbir@amazon.com, shuah@kernel.org,
	 sj38.park@gmail.com, snu@amazon.de,
	Vlastimil Babka <vbabka@suse.cz>,
	 Vladimir Davydov <vdavydov.dev@gmail.com>,
	Yang Shi <yang.shi@linux.alibaba.com>,
	 Huang Ying <ying.huang@intel.com>,
	linux-damon@amazon.com,  Linux MM <linux-mm@kvack.org>,
	linux-doc@vger.kernel.org,  LKML <linux-kernel@vger.kernel.org>
Subject: Re: Re: [PATCH v18 06/14] mm/damon: Implement callbacks for the virtual memory address spaces
Date: Tue, 28 Jul 2020 10:42:11 -0700
Message-ID: <CALvZod7fsGJMKC_oKbr6z_+N_WeGXYBSnMUx7xGxG8KrjY6a0Q@mail.gmail.com> (raw)
In-Reply-To: <20200727090255.24114-1-sjpark@amazon.com>

On Mon, Jul 27, 2020 at 2:03 AM SeongJae Park <sjpark@amazon.com> wrote:
>
> On Mon, 27 Jul 2020 00:34:54 -0700 Greg Thelen <gthelen@google.com> wrote:
>
> > SeongJae Park <sjpark@amazon.com> wrote:
> >
> > > From: SeongJae Park <sjpark@amazon.de>
> > >
> > > 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.
> [...]
> > > diff --git a/mm/damon.c b/mm/damon.c
> > > index b844924b9fdb..386780739007 100644
> > > --- a/mm/damon.c
> > > +++ b/mm/damon.c
> > > @@ -9,6 +9,9 @@
> [...]
> > > +/*
> > > + * Functions for the access checking of the regions
> > > + */
> > > +
> > > +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)) {
> > > +                   clear_page_idle(pte_page(*pte));
> > > +                   set_page_young(pte_page(*pte));
> >
> > While this compiles without support for PG_young and PG_idle, I assume
> > it won't work well because it'd clear pte.young without setting
> > PG_young.  And this would mess with vmscan.
>
> You're right, thanks for catching this up!  This definitely need to be fixed in
> the next spin.
>
> >
> > So this code appears to depend on PG_young and PG_idle, which are
> > currently only available via CONFIG_IDLE_PAGE_TRACKING.  DAMON could
> > depend on CONFIG_IDLE_PAGE_TRACKING via Kconfig.  But I assume that
> > CONFIG_IDLE_PAGE_TRACKING and CONFIG_DAMON cannot be concurrently used
> > because they'll stomp on each other's use of pte.young, PG_young,
> > PG_idle.
> > So I suspect we want:
> > 1. CONFIG_DAMON to depend on !CONFIG_IDLE_PAGE_TRACKING and vise-versa.
> > 2. PG_young,PG_idle and related helpers to depend on
> >    CONFIG_DAMON||CONFIG_IDLE_PAGE_TRACKING.
>
> Awesome insights and suggestions, thanks!
>
> I would like to note that DAMON could be interfered by IDLE_PAGE_TRACKING and
> vmscan, but not vice versa, as DAMON respects PG_idle and PG_young.  This
> design came from the weak goal of DAMON.  DAMON aims to provide not perfect
> monitoring but only best effort accuracy that would be sufficient for
> performance-centric DRAM level memory management.  So, at that time, I thought
> being interfered by IDLE_PAGE_TRACKING and the reclaim logic would not be a
> real problem but letting IDLE_PAGE_TRACKING coexist is somehow beneficial.
> That said, I couldn't find a real benefit of the coexistance yet, and the
> problem of being interference now seems bigger as we will support more cases
> including the page granularity.
>
> Maybe we could make IDLE_PAGE_TRACKING and DAMON coexist but mutual exclusive
> in runtime, if the beneficial of coexistance turns out big.  However, I would
> like to make it simple first and optimize the case later if real requirement
> found.

If you are planning to have support for tracking at page granularity
and physical memory monitoring in DAMON then I don't see any benefit
of coexistence of DAMON with IDLE_PAGE_TRACKING. Though I will not
push you to go that route if the code with coexistence is simple
enough.


  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-13  8:41 [PATCH v18 00/14] Introduce Data Access MONitor (DAMON) SeongJae Park
2020-07-13  8:41 ` [PATCH v18 01/14] mm/page_ext: Export lookup_page_ext() to GPL modules SeongJae Park
2020-07-13 12:08   ` Mike Rapoport
2020-07-13 12:21     ` SeongJae Park
2020-07-13 17:19       ` Mike Rapoport
2020-07-13 17:38         ` SeongJae Park
2020-07-17  9:59           ` SeongJae Park
2020-07-13  8:41 ` [PATCH v18 02/14] mm: Introduce Data Access MONitor (DAMON) SeongJae Park
2020-07-18  2:47   ` Shakeel Butt
2020-07-18 13:31     ` SeongJae Park
2020-07-29 15:31       ` Shakeel Butt
2020-07-29 17:29         ` SeongJae Park
2020-07-13  8:41 ` [PATCH v18 03/14] mm/damon: Implement region based sampling SeongJae Park
2020-07-13  8:41 ` [PATCH v18 04/14] mm/damon: Adaptively adjust regions SeongJae Park
2020-07-13  8:41 ` [PATCH v18 05/14] mm/damon: Track dynamic monitoring target regions update SeongJae Park
2020-07-13  8:41 ` [PATCH v18 06/14] mm/damon: Implement callbacks for the virtual memory address spaces SeongJae Park
2020-07-17  0:46   ` Shakeel Butt
2020-07-17  6:53     ` SeongJae Park
2020-07-17 15:17       ` Shakeel Butt
2020-07-17 16:24         ` SeongJae Park
2020-07-18  2:23           ` Shakeel Butt
2020-07-18  2:51             ` SeongJae Park
2020-07-27  7:34   ` Greg Thelen
2020-07-27  9:02     ` SeongJae Park
2020-07-28 17:42       ` Shakeel Butt [this message]
2020-07-29  6:20         ` SeongJae Park
2020-07-13  8:41 ` [PATCH v18 07/14] mm/damon: Implement access pattern recording SeongJae Park
2020-07-13  8:41 ` [PATCH v18 08/14] mm/damon: Add a tracepoint SeongJae Park
2020-07-13  8:41 ` [PATCH v18 09/14] mm/damon: Implement a debugfs interface SeongJae Park
2020-07-22 10:36   ` SeongJae Park
2020-07-13  8:41 ` [PATCH v18 10/14] tools: Introduce a minimal user-space tool for DAMON SeongJae Park
2020-07-13  8:41 ` [PATCH v18 11/14] Documentation: Add documents " SeongJae Park
2020-07-27  7:19   ` Greg Thelen
2020-07-27  7:38     ` SeongJae Park
2020-07-13  8:41 ` [PATCH v18 12/14] mm/damon: Add kunit tests SeongJae Park
2020-07-13  8:41 ` [PATCH v18 13/14] mm/damon: Add user space selftests SeongJae Park
2020-07-13  8:41 ` [PATCH v18 14/14] MAINTAINERS: Update for DAMON SeongJae Park

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