Re: [PATCH] mm/damon: Add access checking for hugetlb pages

[SeongJae Park <sj@kernel.org>]

On Thu, 16 Dec 2021 09:23:13 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:

> Hi,
> 
> On 12/16/2021 1:16 AM, SeongJae Park wrote:
> > On Wed, 15 Dec 2021 23:23:25 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:
> > 
> >> The process's VMAs can be mapped by hugetlb page, but now the DAMON
> >> did not implement the access checking for hugetlb pte, so we can not
> >> get the actual access count like below if a process VMAs were mapped
> >> by hugetlb.
> >>
> >> damon_aggregated: target_id=18446614368406014464
> >> nr_regions=12 4194304-5476352: 0 545
[...]
> >>
> >> Thus this patch adds hugetlb access checking support, with this patch
> >> we can see below VMA mapped by hugetlb access count.
> >>
> >> damon_aggregated: target_id=18446613056935405824
> >> nr_regions=12 140296486649856-140296489914368: 1 3
[...]
> >> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> >> index 78ff2bc..ee116e5 100644
> >> --- a/mm/damon/vaddr.c
> >> +++ b/mm/damon/vaddr.c
> >> @@ -14,6 +14,7 @@
> >>   #include <linux/page_idle.h>
> >>   #include <linux/pagewalk.h>
> >>   #include <linux/sched/mm.h>
> >> +#include <linux/hugetlb.h>
> >>   
> >>   #include "prmtv-common.h"
> >>   
> >> @@ -386,8 +387,33 @@ static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
> >>   	return 0;
> >>   }
> >>   
> >> +#ifdef CONFIG_HUGETLB_PAGE
> >> +static int damon_mkold_hugetlb_entry(pte_t *pte, unsigned long hmask,
> >> +				     unsigned long addr, unsigned long end,
> >> +				     struct mm_walk *walk)
> >> +{
> >> +	struct hstate *h = hstate_vma(walk->vma);
> >> +	spinlock_t *ptl;
> >> +	pte_t entry;
> >> +
> >> +	ptl = huge_pte_lock(h, walk->mm, pte);
> >> +	entry = huge_ptep_get(pte);
> > 
> > Could we do above assignments in the variables definitions?
> 
> Since we need get the hugetlb pte under the pte lock, I still perfer to 
> declare the lock region explicitly in the code instead in the variables 
> definitions.

Ok, that makes sense.

[...]
> >> +#ifdef CONFIG_HUGETLB_PAGE
> >> +static int damon_young_hugetlb_entry(pte_t *pte, unsigned long hmask,
> >> +				     unsigned long addr, unsigned long end,
> >> +				     struct mm_walk *walk)
> >> +{
> >> +	struct damon_young_walk_private *priv = walk->private;
> >> +	struct hstate *h = hstate_vma(walk->vma);
> >> +	struct page *page;
> >> +	spinlock_t *ptl;
> >> +	pte_t entry;
> >> +
> >> +	ptl = huge_pte_lock(h, walk->mm, pte);
> >> +	entry = huge_ptep_get(pte);
> > 
> > Could we do these assignments in the above variables definitions?
> 
> Ditto.

Again, agreed.

> 
> Thanks for your comments.

My pleaseure!


Thanks,
SJ