Re: [PATCH v3 2/4] mm/page_reporting: Export reporting order as module parameter

[Alexander Duyck <alexander.duyck@gmail.com>]

On Tue, Jun 22, 2021 at 5:34 PM Gavin Shan <gshan@redhat.com> wrote:
>
> The macro PAGE_REPORTING_MIN_ORDER is defined as the page reporting
> threshold. It can't be adjusted at runtime.
>
> This introduces a variable (@page_reporting_order) to replace the
> marcro (PAGE_REPORTING_MIN_ORDER). It's also exported so that the
> page reporting order can be adjusted at runtime.
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
>  mm/page_reporting.c                             | 8 ++++++--
>  mm/page_reporting.h                             | 5 ++---
>  3 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index cb89dbdedc46..566c4b9af3cd 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3566,6 +3566,12 @@
>                         off: turn off poisoning (default)
>                         on: turn on poisoning
>
> +       page_reporting.page_reporting_order=
> +                       [KNL] Minimal page reporting order
> +                       Format: <integer>
> +                       Adjust the minimal page reporting order. The page
> +                       reporting is disabled when it exceeds (MAX_ORDER-1).
> +

Based on the issue found by Stephen I think we may need to tweak this
a bit. I think we may want to just default this value to MAX_ORDER. We
can override this value at registration time with the value provided
either by the reporting device or pageblock_order if prdev->order is
not set.

> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> index df9c5054e1b4..293a8713ef7c 100644
> --- a/mm/page_reporting.c
> +++ b/mm/page_reporting.c
> @@ -10,6 +10,10 @@
>  #include "page_reporting.h"
>  #include "internal.h"
>
> +unsigned int page_reporting_order = pageblock_order;

Rather than setting this to pageblock_order directly you can set this
to MAX_ORDER which should be constant. Then we can just add some
checks in page_reporting_register to update it when pageblock_order is
less than page_reporting_order.

Then in the next patch you could tweak it so that it will use
"prdev->order ? : pageblock_order" instead of just pageblock_order.