linux-kernel - Re: [PATCH v5 02/14] mm/damon: Implement region based sampling

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Date:   Fri, 21 Feb 2020 14:51:42 +0100
From:   SeongJae Park <sjpark@...zon.com>
To:     SeongJae Park <sjpark@...zon.com>
CC:     <akpm@...ux-foundation.org>, SeongJae Park <sjpark@...zon.de>,
        <acme@...nel.org>, <alexander.shishkin@...ux.intel.com>,
        <amit@...nel.org>, <brendan.d.gregg@...il.com>,
        <brendanhiggins@...gle.com>, <cai@....pw>,
        <colin.king@...onical.com>, <corbet@....net>, <dwmw@...zon.com>,
        <jolsa@...hat.com>, <kirill@...temov.name>, <mark.rutland@....com>,
        <mgorman@...e.de>, <minchan@...nel.org>, <mingo@...hat.com>,
        <namhyung@...nel.org>, <peterz@...radead.org>,
        <rdunlap@...radead.org>, <rostedt@...dmis.org>, <shuah@...nel.org>,
        <sj38.park@...il.com>, <vdavydov.dev@...il.com>,
        <linux-mm@...ck.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 02/14] mm/damon: Implement region based sampling

On Mon, 17 Feb 2020 11:25:32 +0100 SeongJae Park <sjpark@...zon.com> wrote:

> From: SeongJae Park <sjpark@...zon.de>
> 
> This commit implements DAMON's basic access check and region based
> sampling mechanisms.  This change would seems make no sense, mainly
> because it is only a part of the DAMON's logics.  Following two commits
> will make more sense.
> 
[...]
> +/*
> + * Check whether the given region has accessed since the last check
> + *
> + * mm	'mm_struct' for the given virtual address space
> + * r	the region to be checked
> + */
> +static void kdamond_check_access(struct damon_ctx *ctx,
> +			struct mm_struct *mm, struct damon_region *r)
> +{
> +	pte_t *pte = NULL;
> +	pmd_t *pmd = NULL;
> +	spinlock_t *ptl;
> +
> +	if (follow_pte_pmd(mm, r->sampling_addr, NULL, &pte, &pmd, &ptl))
> +		goto mkold;
> +
> +	/* Read the page table access bit of the page */
> +	if (pte && pte_young(*pte))
> +		r->nr_accesses++;
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	else if (pmd && pmd_young(*pmd))
> +		r->nr_accesses++;
> +#endif	/* CONFIG_TRANSPARENT_HUGEPAGE */
> +
> +	spin_unlock(ptl);
> +
> +mkold:
> +	/* mkold next target */
> +	r->sampling_addr = damon_rand(ctx, r->vm_start, r->vm_end);
> +
> +	if (follow_pte_pmd(mm, r->sampling_addr, NULL, &pte, &pmd, &ptl))
> +		return;
> +
> +	if (pte) {
> +		if (pte_young(*pte)) {
> +			clear_page_idle(pte_page(*pte));
> +			set_page_young(pte_page(*pte));
> +		}
> +		*pte = pte_mkold(*pte);
> +	}
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	else if (pmd) {
> +		if (pmd_young(*pmd)) {
> +			clear_page_idle(pmd_page(*pmd));
> +			set_page_young(pte_page(*pte));

Oops, This should be `set_page_young(pmd_page(*pmd))`.  Will fix in next spin.


Thanks,
SeongJae Park