On Tue, Jan 5, 2021 at 7:47 PM Liang Li <liliang324@xxxxxxxxx> wrote:
>
> Use the page order as the only threshold for page reporting
> is not flexible and has some flaws. Because scan a long free
> list is not cheap, it's better to wake up the page reporting
> worker when there are more pages, wake it up for a sigle page
> may not worth.
> This patch add a batch size as another threshold to control the
> waking up of reporting worker.
>
> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Liang Li <liliang324@xxxxxxxxx>
> Signed-off-by: Liang Li <liliangleo@xxxxxxxxxxxxxx>
So you are going to need a lot more explanation for this. Page
reporting already had the concept of batching as you could only scan
once every 2 seconds as I recall. Thus the "PAGE_REPORTING_DELAY". The
change you are making doesn't make any sense without additional
context.
> ---
> mm/page_reporting.c | 1 +
> mm/page_reporting.h | 12 ++++++++++--
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> index cd8e13d41df4..694df981ddd2 100644
> --- a/mm/page_reporting.c
> +++ b/mm/page_reporting.c
> @@ -12,6 +12,7 @@
>
> #define PAGE_REPORTING_DELAY (2 * HZ)
> static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
> +unsigned long page_report_batch_size __read_mostly = 16 * 1024 * 1024UL;
>
> enum {
> PAGE_REPORTING_IDLE = 0,
> diff --git a/mm/page_reporting.h b/mm/page_reporting.h
> index 2c385dd4ddbd..b8fb3bbb345f 100644
> --- a/mm/page_reporting.h
> +++ b/mm/page_reporting.h
> @@ -12,6 +12,8 @@
>
> #define PAGE_REPORTING_MIN_ORDER pageblock_order
>
> +extern unsigned long page_report_batch_size;
> +
> #ifdef CONFIG_PAGE_REPORTING
> DECLARE_STATIC_KEY_FALSE(page_reporting_enabled);
> void __page_reporting_notify(void);
> @@ -33,6 +35,8 @@ static inline bool page_reported(struct page *page)
> */
> static inline void page_reporting_notify_free(unsigned int order)
> {
> + static long batch_size;
> +
I'm not sure this makes a tone of sense to place the value in an
inline function. It might make more sense to put this new code in
__page_reporting_notify so that all callers would be referring to the
same batch_size value and you don't have to bother with the export of
the page_report_batch_size value.
> /* Called from hot path in __free_one_page() */
> if (!static_branch_unlikely(&page_reporting_enabled))
> return;
> @@ -41,8 +45,12 @@ static inline void page_reporting_notify_free(unsigned int order)
> if (order < PAGE_REPORTING_MIN_ORDER)
> return;
>
> - /* This will add a few cycles, but should be called infrequently */
> - __page_reporting_notify();
> + batch_size += (1 << order) << PAGE_SHIFT;
> + if (batch_size >= page_report_batch_size) {
> + batch_size = 0;
I would probably run this in the opposite direction. Rather than
running batch_size to zero I would look at adding a "batch_remaining"
and then when it is < 0 you could then reset it back to
page_report_batch_size. Doing that you only have to read one variable
most of the time instead of doing a comparison against two.
> + /* This add a few cycles, but should be called infrequently */
> + __page_reporting_notify();
> + }
> }
> #else /* CONFIG_PAGE_REPORTING */
> #define page_reported(_page) false
> --
> 2.18.2
>
>
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