Messages in this thread | | | Subject | Re: [PATCH v2 2/3] mm/page_reporting: Allow driver to specify threshold | From | Gavin Shan <> | Date | Wed, 23 Jun 2021 10:43:48 +1000 |
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On 6/23/21 3:39 AM, Alexander Duyck wrote: > On Mon, Jun 21, 2021 at 10:48 PM Gavin Shan <gshan@redhat.com> wrote: >> >> The page reporting threshold is currently sticky to @pageblock_order. >> The page reporting can never be triggered because the freeing page >> can't come up with a free area like that huge. The situation becomes >> worse when the system memory becomes heavily fragmented. >> >> For example, the following configurations are used on ARM64 when 64KB >> base page size is enabled. In this specific case, the page reporting >> won't be triggered until the freeing page comes up with a 512MB free >> area. That's hard to be met, especially when the system memory becomes >> heavily fragmented. >> >> PAGE_SIZE: 64KB >> HPAGE_SIZE: 512MB >> pageblock_order: 13 (512MB) >> MAX_ORDER: 14 >> >> This allows the drivers to specify the threshold when the page >> reporting device is registered. The threshold falls back to >> @pageblock_order if it's not specified by the driver. The existing >> users (hv_balloon and virtio_balloon) don't specify the threshold >> and @pageblock_order is still taken as their page reporting order. >> So this shouldn't introduce functional changes. >> >> Signed-off-by: Gavin Shan <gshan@redhat.com> >> --- >> include/linux/page_reporting.h | 3 +++ >> mm/page_reporting.c | 14 ++++++++++---- >> mm/page_reporting.h | 10 ++-------- >> 3 files changed, 15 insertions(+), 12 deletions(-) >> >> diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h >> index 3b99e0ec24f2..fe648dfa3a7c 100644 >> --- a/include/linux/page_reporting.h >> +++ b/include/linux/page_reporting.h >> @@ -18,6 +18,9 @@ struct page_reporting_dev_info { >> >> /* Current state of page reporting */ >> atomic_t state; >> + >> + /* Minimal order of page reporting */ >> + unsigned int order; >> }; >> >> /* Tear-down and bring-up for page reporting devices */ >> diff --git a/mm/page_reporting.c b/mm/page_reporting.c >> index df9c5054e1b4..27670360bae6 100644 >> --- a/mm/page_reporting.c >> +++ b/mm/page_reporting.c > > <snip> > >> @@ -324,6 +324,12 @@ int page_reporting_register(struct page_reporting_dev_info *prdev) >> goto err_out; >> } >> >> + /* >> + * We need to choose the minimal order of page reporting if it's >> + * not specified by the driver. >> + */ >> + prdev->order = prdev->order ? prdev->order : pageblock_order; >> + >> /* initialize state and work structures */ >> atomic_set(&prdev->state, PAGE_REPORTING_IDLE); >> INIT_DELAYED_WORK(&prdev->work, &page_reporting_process); > > Rather than using prdev->order directly it might be better to have a > reporting_order value you could export for use by > page_reporting_notify_free. That way you avoid the overhead of having > to make a function call per page freed. >
Yes, I obviously missed the point to reduce the overhead because of function call. In next revision, I will introduce @page_reporting_order for this. Besides, it will be exported as a module parameter so that it can be changed dynamically, as David suggested before.
>> diff --git a/mm/page_reporting.h b/mm/page_reporting.h >> index 2c385dd4ddbd..d9f972e72649 100644 >> --- a/mm/page_reporting.h >> +++ b/mm/page_reporting.h >> @@ -10,11 +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); >> -void __page_reporting_notify(void); >> +void __page_reporting_notify(unsigned int order); >> >> static inline bool page_reported(struct page *page) >> { >> @@ -37,12 +35,8 @@ static inline void page_reporting_notify_free(unsigned int order) >> if (!static_branch_unlikely(&page_reporting_enabled)) >> return; >> >> - /* Determine if we have crossed reporting threshold */ >> - if (order < PAGE_REPORTING_MIN_ORDER) >> - return; >> - >> /* This will add a few cycles, but should be called infrequently */ >> - __page_reporting_notify(); >> + __page_reporting_notify(order); >> } >> #else /* CONFIG_PAGE_REPORTING */ >> #define page_reported(_page) false > > With us making the function call per page freed we are likely to have > a much more significant impact on performance with page reporting > enabled. Ideally we want to limit this impact so that we only take the > cost for the conditional check on the lower order pages. >
Yep, thanks for the explanation, Alex.
Thanks, Gavin
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