linux-kernel - Re: [RFC v7 06/10] mm/damon: Implement callbacks for physical memory monitoring

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Message-ID: <CALvZod5ZRUHO+=Bvwj4aEKNL0Egwea2dZKuYDKhkvvUyezbgdg@mail.gmail.com>
Date:   Wed, 19 Aug 2020 17:26:15 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     SeongJae Park <sjpark@...zon.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        Andrea Arcangeli <aarcange@...hat.com>, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, amit@...nel.org,
        benh@...nel.crashing.org, brendan.d.gregg@...il.com,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Qian Cai <cai@....pw>,
        Colin Ian King <colin.king@...onical.com>,
        Jonathan Corbet <corbet@....net>,
        David Hildenbrand <david@...hat.com>, dwmw@...zon.com,
        "Du, Fan" <fan.du@...el.com>, foersleo@...zon.de,
        Greg Thelen <gthelen@...gle.com>,
        Ian Rogers <irogers@...gle.com>, jolsa@...hat.com,
        "Kirill A. Shutemov" <kirill@...temov.name>, mark.rutland@....com,
        Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, namhyung@...nel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        David Rientjes <rientjes@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>, rppt@...nel.org,
        sblbir@...zon.com, shuah@...nel.org, sj38.park@...il.com,
        snu@...zon.de, Vlastimil Babka <vbabka@...e.cz>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Huang Ying <ying.huang@...el.com>, zgf574564920@...il.com,
        linux-damon@...zon.com, Linux MM <linux-mm@...ck.org>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v7 06/10] mm/damon: Implement callbacks for physical memory monitoring

On Tue, Aug 18, 2020 at 12:27 AM SeongJae Park <sjpark@...zon.com> wrote:
>
> From: SeongJae Park <sjpark@...zon.de>
>
> This commit implements the four callbacks (->init_target_regions,
> ->update_target_regions, ->prepare_access_check, and ->check_accesses)
> for the basic access monitoring of the physical memory address space.
> By setting the callback pointers to point those, users can easily
> monitor the accesses to the physical memory.
>
> Internally, it uses the PTE Accessed bit, as similar to that of the
> virtual memory support.  Also, it supports only user memory pages, as
> idle page tracking also does, for the same reason.  If the monitoring
> target physical memory address range contains non-user memory pages,
> access check of the pages will do nothing but simply treat the pages as
> not accessed.
>
> Users who want to use other access check primitives and/or monitor the
> non-user memory regions could implement and use their own callbacks.
>
> Signed-off-by: SeongJae Park <sjpark@...zon.de>
[snip]
> +static void damon_phys_mkold(unsigned long paddr)
> +{
> +       struct page *page = damon_phys_get_page(PHYS_PFN(paddr));
> +       struct rmap_walk_control rwc = {
> +               .rmap_one = damon_page_mkold,
> +               .anon_lock = page_lock_anon_vma_read,
> +       };
> +       bool need_lock;
> +
> +       if (!page)
> +               return;
> +
> +       if (!page_mapped(page) || !page_rmapping(page))
> +               return;

I don't think you want to skip the unmapped pages. The point of
physical address space monitoring was to include the monitoring of
unmapped pages, so, skipping them invalidates the underlying
motivation.

> +
> +       need_lock = !PageAnon(page) || PageKsm(page);
> +       if (need_lock && !trylock_page(page))
> +               return;
> +
> +       rmap_walk(page, &rwc);
> +
> +       if (need_lock)
> +               unlock_page(page);
> +       put_page(page);
> +}
> +
[snip]
> +
> +static bool damon_phys_young(unsigned long paddr, unsigned long *page_sz)
> +{
> +       struct page *page = damon_phys_get_page(PHYS_PFN(paddr));
> +       struct damon_phys_access_chk_result result = {
> +               .page_sz = PAGE_SIZE,
> +               .accessed = false,
> +       };
> +       struct rmap_walk_control rwc = {
> +               .arg = &result,
> +               .rmap_one = damon_page_accessed,
> +               .anon_lock = page_lock_anon_vma_read,
> +       };
> +       bool need_lock;
> +
> +       if (!page)
> +               return false;
> +
> +       if (!page_mapped(page) || !page_rmapping(page))
> +               return false;

Same here.

> +
> +       need_lock = !PageAnon(page) || PageKsm(page);
> +       if (need_lock && !trylock_page(page))
> +               return false;
> +
> +       rmap_walk(page, &rwc);
> +
> +       if (need_lock)
> +               unlock_page(page);
> +       put_page(page);
> +
> +       *page_sz = result.page_sz;
> +       return result.accessed;
> +}
> +