linux-kernel - Re: [RFC v2 7/9] mm/damon: Implement callbacks for physical memory monitoring

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Message-ID: <bd640661-143f-882f-ed92-3d2791b173aa@redhat.com>
Date:   Wed, 3 Jun 2020 18:09:21 +0200
From:   David Hildenbrand <david@...hat.com>
To:     SeongJae Park <sjpark@...zon.com>, akpm@...ux-foundation.org
Cc:     SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        aarcange@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, amit@...nel.org,
        benh@...nel.crashing.org, brendan.d.gregg@...il.com,
        brendanhiggins@...gle.com, cai@....pw, colin.king@...onical.com,
        corbet@....net, dwmw@...zon.com, foersleo@...zon.de,
        irogers@...gle.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, riel@...riel.com, rientjes@...gle.com,
        rostedt@...dmis.org, sblbir@...zon.com, shakeelb@...gle.com,
        shuah@...nel.org, sj38.park@...il.com, snu@...zon.de,
        vbabka@...e.cz, vdavydov.dev@...il.com, yang.shi@...ux.alibaba.com,
        ying.huang@...el.com, linux-damon@...zon.com, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 7/9] mm/damon: Implement callbacks for physical memory
 monitoring

On 03.06.20 16:11, SeongJae Park 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 page frames that
> supported by idle page tracking.  Acutally, most of the code is stollen
> from idle page tracking.  Users who want to use other access check
> primitives and monitor the frames that not supported with this
> implementation could implement their own callbacks on their own.
> 
> Signed-off-by: SeongJae Park <sjpark@...zon.de>
> ---
>  include/linux/damon.h |   5 ++
>  mm/damon.c            | 184 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 189 insertions(+)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 1a788bfd1b4e..f96503a532ea 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -216,6 +216,11 @@ void kdamond_update_vm_regions(struct damon_ctx *ctx);
>  void kdamond_prepare_vm_access_checks(struct damon_ctx *ctx);
>  unsigned int kdamond_check_vm_accesses(struct damon_ctx *ctx);
>  
> +void kdamond_init_phys_regions(struct damon_ctx *ctx);
> +void kdamond_update_phys_regions(struct damon_ctx *ctx);
> +void kdamond_prepare_phys_access_checks(struct damon_ctx *ctx);
> +unsigned int kdamond_check_phys_accesses(struct damon_ctx *ctx);
> +
>  int damon_set_pids(struct damon_ctx *ctx, int *pids, ssize_t nr_pids);
>  int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
>  		unsigned long aggr_int, unsigned long regions_update_int,
> diff --git a/mm/damon.c b/mm/damon.c
> index f5cbc97a3bbc..6a5c6d540580 100644
> --- a/mm/damon.c
> +++ b/mm/damon.c
> @@ -19,7 +19,9 @@
>  #include <linux/mm.h>
>  #include <linux/module.h>
>  #include <linux/page_idle.h>
> +#include <linux/pagemap.h>
>  #include <linux/random.h>
> +#include <linux/rmap.h>
>  #include <linux/sched/mm.h>
>  #include <linux/sched/task.h>
>  #include <linux/slab.h>
> @@ -480,6 +482,11 @@ void kdamond_init_vm_regions(struct damon_ctx *ctx)
>  	}
>  }
>  
> +/* Do nothing.  Users should set the initial regions by themselves */
> +void kdamond_init_phys_regions(struct damon_ctx *ctx)
> +{
> +}
> +
>  static void damon_mkold(struct mm_struct *mm, unsigned long addr)
>  {
>  	pte_t *pte = NULL;
> @@ -611,6 +618,178 @@ unsigned int kdamond_check_vm_accesses(struct damon_ctx *ctx)
>  	return max_nr_accesses;
>  }
>  
> +/* access check functions for physical address based regions */
> +
> +/* This code is stollen from page_idle.c */
> +static struct page *damon_phys_get_page(unsigned long pfn)
> +{
> +	struct page *page;
> +	pg_data_t *pgdat;
> +
> +	if (!pfn_valid(pfn))
> +		return NULL;
> +

Who provides these pfns? Can these be random pfns, supplied unchecked by
user space? Or are they at least mapped into some user space process?

IOW, do we need a pfn_to_online_page() to make sure the memmap even was
initialized?

-- 
Thanks,

David / dhildenb