Re: [PATCH v4 2/4] mm/page_reporting: Export reporting order as module parameter

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

On Thu, Jun 24, 2021 at 4:46 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). MAX_ORDER is assigned to it initially,
> meaning the page reporting is disabled. It will be specified by driver
> if valid one is provided. Otherwise, it will fall back to @pageblock_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>
> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>

So this patch looks like it is technically broken. We need a line in
page_reporting_register that will overwrite the value with
pageblock_order if it is less than page_reporting_order.

> ---
>  Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
>  mm/page_reporting.c                             | 9 +++++++--
>  mm/page_reporting.h                             | 5 ++---
>  3 files changed, 15 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).
> +
>         panic=          [KNL] Kernel behaviour on panic: delay <timeout>
>                         timeout > 0: seconds before rebooting
>                         timeout = 0: wait forever
> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> index df9c5054e1b4..34bf4d26c2c4 100644
> --- a/mm/page_reporting.c
> +++ b/mm/page_reporting.c
> @@ -4,12 +4,17 @@
>  #include <linux/page_reporting.h>
>  #include <linux/gfp.h>
>  #include <linux/export.h>
> +#include <linux/module.h>
>  #include <linux/delay.h>
>  #include <linux/scatterlist.h>
>
>  #include "page_reporting.h"
>  #include "internal.h"
>
> +unsigned int page_reporting_order = MAX_ORDER;
> +module_param(page_reporting_order, uint, 0644);
> +MODULE_PARM_DESC(page_reporting_order, "Set page reporting order");
> +
>  #define PAGE_REPORTING_DELAY   (2 * HZ)
>  static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
>
> @@ -229,7 +234,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
>
>         /* Generate minimum watermark to be able to guarantee progress */
>         watermark = low_wmark_pages(zone) +
> -                   (PAGE_REPORTING_CAPACITY << PAGE_REPORTING_MIN_ORDER);
> +                   (PAGE_REPORTING_CAPACITY << page_reporting_order);
>
>         /*
>          * Cancel request if insufficient free memory or if we failed
> @@ -239,7 +244,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
>                 return err;
>
>         /* Process each free list starting from lowest order/mt */
> -       for (order = PAGE_REPORTING_MIN_ORDER; order < MAX_ORDER; order++) {
> +       for (order = page_reporting_order; order < MAX_ORDER; order++) {
>                 for (mt = 0; mt < MIGRATE_TYPES; mt++) {
>                         /* We do not pull pages from the isolate free list */
>                         if (is_migrate_isolate(mt))
> diff --git a/mm/page_reporting.h b/mm/page_reporting.h
> index 2c385dd4ddbd..c51dbc228b94 100644
> --- a/mm/page_reporting.h
> +++ b/mm/page_reporting.h
> @@ -10,10 +10,9 @@
>  #include <linux/pgtable.h>
>  #include <linux/scatterlist.h>
>
> -#define PAGE_REPORTING_MIN_ORDER       pageblock_order
> -
>  #ifdef CONFIG_PAGE_REPORTING
>  DECLARE_STATIC_KEY_FALSE(page_reporting_enabled);
> +extern unsigned int page_reporting_order;
>  void __page_reporting_notify(void);
>
>  static inline bool page_reported(struct page *page)
> @@ -38,7 +37,7 @@ static inline void page_reporting_notify_free(unsigned int order)
>                 return;
>
>         /* Determine if we have crossed reporting threshold */
> -       if (order < PAGE_REPORTING_MIN_ORDER)
> +       if (order < page_reporting_order)
>                 return;
>
>         /* This will add a few cycles, but should be called infrequently */
> --
> 2.23.0
>