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From:   SeongJae Park <sjpark@amazon.com>
To:     David Hildenbrand <david@redhat.com>
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Subject: Re: Re: [RFC v2 7/9] mm/damon: Implement callbacks for physical memory monitoring
Date:   Thu, 4 Jun 2020 09:26:11 +0200
Message-ID: <20200604072611.11049-1-sjpark@amazon.com>
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On Wed, 3 Jun 2020 18:09:21 +0200 David Hildenbrand <david@redhat.com> wrote:

> 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?

Your guess is right, users can give random physical address and that will be
translated into pfn.

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

Thank you for pointing out this!  I will use it in the next spin.  Also, this
code is stollen from page_idle_get_page().  Seems like it should also be
modified to use it.  I will send the patch for it, either.


Thanks,
SeongJae Park

> 
> -- 
> Thanks,
> 
> David / dhildenb