From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> Subject: mm/page_reporting: add budget limit on how many pages can be reported per pass In order to keep ourselves from reporting pages that are just going to be reused again in the case of heavy churn we can put a limit on how many total pages we will process per pass. Doing this will allow the worker thread to go into idle much more quickly so that we avoid competing with other threads that might be allocating or freeing pages. The logic added here will limit the worker thread to no more than one sixteenth of the total free pages in a given area per list. Once that limit is reached it will update the state so that at the end of the pass we will reschedule the worker to try again in 2 seconds when the memory churn has hopefully settled down. Again this optimization doesn't show much of a benefit in the standard case as the memory churn is minmal. However with page allocator shuffling enabled the gain is quite noticeable. Below are the results with a THP enabled version of the will-it-scale page_fault1 test showing the improvement in iterations for 16 processes or threads. Without: tasks processes processes_idle threads threads_idle 16 8283274.75 0.17 5594261.00 38.15 With: tasks processes processes_idle threads threads_idle 16 8767010.50 0.21 5791312.75 36.98 Link: http://lkml.kernel.org/r/20200211224719.29318.72113.stgit@localhost.localdomain Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> Acked-by: 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: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Nitesh Narayan Lal <nitesh@xxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Pankaj Gupta <pagupta@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Wei Wang <wei.w.wang@xxxxxxxxx> Cc: Yang Zhang <yang.zhang.wz@xxxxxxxxx> Cc: wei qi <weiqi4@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/page_reporting.h | 1 mm/page_reporting.c | 33 ++++++++++++++++++++++++++++++- 2 files changed, 33 insertions(+), 1 deletion(-) --- a/include/linux/page_reporting.h~mm-page_reporting-add-budget-limit-on-how-many-pages-can-be-reported-per-pass +++ a/include/linux/page_reporting.h @@ -5,6 +5,7 @@ #include <linux/mmzone.h> #include <linux/scatterlist.h> +/* This value should always be a power of 2, see page_reporting_cycle() */ #define PAGE_REPORTING_CAPACITY 32 struct page_reporting_dev_info { --- a/mm/page_reporting.c~mm-page_reporting-add-budget-limit-on-how-many-pages-can-be-reported-per-pass +++ a/mm/page_reporting.c @@ -114,6 +114,7 @@ page_reporting_cycle(struct page_reporti struct list_head *list = &area->free_list[mt]; unsigned int page_len = PAGE_SIZE << order; struct page *page, *next; + long budget; int err = 0; /* @@ -125,12 +126,39 @@ page_reporting_cycle(struct page_reporti spin_lock_irq(&zone->lock); + /* + * Limit how many calls we will be making to the page reporting + * device for this list. By doing this we avoid processing any + * given list for too long. + * + * The current value used allows us enough calls to process over a + * sixteenth of the current list plus one additional call to handle + * any pages that may have already been present from the previous + * list processed. This should result in us reporting all pages on + * an idle system in about 30 seconds. + * + * The division here should be cheap since PAGE_REPORTING_CAPACITY + * should always be a power of 2. + */ + budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16); + /* loop through free list adding unreported pages to sg list */ list_for_each_entry_safe(page, next, list, lru) { /* We are going to skip over the reported pages. */ if (PageReported(page)) continue; + /* + * If we fully consumed our budget then update our + * state to indicate that we are requesting additional + * processing and exit this list. + */ + if (budget < 0) { + atomic_set(&prdev->state, PAGE_REPORTING_REQUESTED); + next = page; + break; + } + /* Attempt to pull page from list and place in scatterlist */ if (*offset) { if (!__isolate_free_page(page, order)) { @@ -146,7 +174,7 @@ page_reporting_cycle(struct page_reporti } /* - * Make the first non-processed page in the free list + * Make the first non-reported page in the free list * the new head of the free list before we release the * zone lock. */ @@ -162,6 +190,9 @@ page_reporting_cycle(struct page_reporti /* reset offset since the full list was reported */ *offset = PAGE_REPORTING_CAPACITY; + /* update budget to reflect call to report function */ + budget--; + /* reacquire zone lock and resume processing */ spin_lock_irq(&zone->lock); _
