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

[David Hildenbrand <david@redhat.com>]

On 03.06.20 16:11, SeongJae Park wrote:
> From: SeongJae Park <sjpark@amazon.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@amazon.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