Re: [RFC PATCH v3 04/37] mm/damon/core: implement damon_report_page_fault()

[JaeJoon Jung]

On Mon, 8 Dec 2025 at 15:33, SeongJae Park <sj@xxxxxxxxxx> wrote:
>
> Implement a DAMON core API for reporting page fault events to DAMON.  It
> is a wrapper of damon_report_access().
>
> This is a temporal hack.  In future versions that will have no RFC tag,
> only damon_report_access() may be used.

It's a minor, but git am throws an error when applying the [RFC PATCH v3 04/37]
patch file.  I am testing it by modifying it as follows.
damon_report_access() is
called by damon_report_page_fault(), so they depend on each other.

#ifdef CONFIG_MMU
void damon_report_access(struct damon_access_report *report);
void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd);
#else
static inline void damon_report_access(struct damon_access_report *report)
{
}
static inline void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd)
{
}
#endif

Thanks,
JaeJoon

>
> Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
> ---
>  include/linux/damon.h | 10 ++++++++++
>  mm/damon/core.c       | 17 +++++++++++++++++
>  2 files changed, 27 insertions(+)
>
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index b9359c76a6f1..b8ebb2aa02c8 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -1017,6 +1017,13 @@ int damon_call(struct damon_ctx *ctx, struct damon_call_control *control);
>  int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control);
>
>  void damon_report_access(struct damon_access_report *report);
> +#ifdef CONFIG_MMU
> +void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd);
> +#else
> +static inline void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd)
> +{
> +}
> +#endif
>
>  int damon_set_region_biggest_system_ram_default(struct damon_target *t,
>                                 unsigned long *start, unsigned long *end,
> @@ -1027,6 +1034,9 @@ int damon_set_region_biggest_system_ram_default(struct damon_target *t,
>  static inline void damon_report_access(struct damon_access_report *report)
>  {
>  }
> +static inline void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd)
> +{
> +}
>
>  #endif /* CONFIG_DAMON */
>
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 89305d42e116..296117d5e7f7 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -1579,6 +1579,23 @@ void damon_report_access(struct damon_access_report *report)
>         mutex_unlock(&damon_access_reports_lock);
>  }
>
> +#ifdef CONFIG_MMU
> +void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd)
> +{
> +       struct damon_access_report access_report = {
> +               .size = 1,      /* todo: set appripriately */
> +       };
> +
> +       if (huge_pmd)
> +               access_report.addr = PFN_PHYS(pmd_pfn(vmf->orig_pmd));
> +       else
> +               access_report.addr = PFN_PHYS(pte_pfn(vmf->orig_pte));
> +       /* todo: report vmf->address as virtual address */
> +
> +       damon_report_access(&access_report);
> +}
> +#endif
> +
>  /*
>   * Warn and fix corrupted ->nr_accesses[_bp] for investigations and preventing
>   * the problem being propagated.
> --
> 2.47.3
>