// SPDX-License-Identifier: GPL-2.0 #include <linux/mm.h> #include <linux/mmzone.h> #include <linux/page_reporting.h> #include <linux/gfp.h> #include <linux/export.h> #include <linux/delay.h> #include <linux/scatterlist.h> #include "page_reporting.h" #include "internal.h" #define PAGE_REPORTING_DELAY (2 * HZ) static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly; enum { PAGE_REPORTING_IDLE = 0, PAGE_REPORTING_REQUESTED, PAGE_REPORTING_ACTIVE }; /* request page reporting */ static void __page_reporting_request(struct page_reporting_dev_info *prdev) { unsigned int state; /* Check to see if we are in desired state */ state = atomic_read(&prdev->state); if (state == PAGE_REPORTING_REQUESTED) return; /* * If reporting is already active there is nothing we need to do. * Test against 0 as that represents PAGE_REPORTING_IDLE. */ state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED); if (state != PAGE_REPORTING_IDLE) return; /* * Delay the start of work to allow a sizable queue to build. For * now we are limiting this to running no more than once every * couple of seconds. */ schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY); } /* notify prdev of free page reporting request */ void __page_reporting_notify(void) { struct page_reporting_dev_info *prdev; /* * We use RCU to protect the pr_dev_info pointer. In almost all * cases this should be present, however in the unlikely case of * a shutdown this will be NULL and we should exit. */ rcu_read_lock(); prdev = rcu_dereference(pr_dev_info); if (likely(prdev)) __page_reporting_request(prdev); rcu_read_unlock(); } static void page_reporting_drain(struct page_reporting_dev_info *prdev, struct scatterlist *sgl, unsigned int nents, bool reported) { struct scatterlist *sg = sgl; /* * Drain the now reported pages back into their respective * free lists/areas. We assume at least one page is populated. */ do { struct page *page = sg_page(sg); int mt = get_pageblock_migratetype(page); unsigned int order = get_order(sg->length); __putback_isolated_page(page, order, mt); /* If the pages were not reported due to error skip flagging */ if (!reported) continue; /* * If page was not comingled with another page we can * consider the result to be "reported" since the page * hasn't been modified, otherwise we will need to * report on the new larger page when we make our way * up to that higher order. */ if (PageBuddy(page) && buddy_order(page) == order) __SetPageReported(page); } while ((sg = sg_next(sg))); /* reinitialize scatterlist now that it is empty */ sg_init_table(sgl, nents); } /* * The page reporting cycle consists of 4 stages, fill, report, drain, and * idle. We will cycle through the first 3 stages until we cannot obtain a * full scatterlist of pages, in that case we will switch to idle. */ static int page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone, unsigned int order, unsigned int mt, struct scatterlist *sgl, unsigned int *offset) { struct free_area *area = &zone->free_area[order]; struct list_head *list = &area->free_list[mt]; unsigned int page_len = PAGE_SIZE << order; struct page *page, *next; long budget; int err = 0; /* * Perform early check, if free area is empty there is * nothing to process so we can skip this free_list. */ if (list_empty(list)) return err; 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)) { next = page; break; } /* Add page to scatter list */ --(*offset); sg_set_page(&sgl[*offset], page, page_len, 0); continue; } /* * Make the first non-reported page in the free list * the new head of the free list before we release the * zone lock. */ if (!list_is_first(&page->lru, list)) list_rotate_to_front(&page->lru, list); /* release lock before waiting on report processing */ spin_unlock_irq(&zone->lock); /* begin processing pages in local list */ err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY); /* 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); /* flush reported pages from the sg list */ page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err); /* * Reset next to first entry, the old next isn't valid * since we dropped the lock to report the pages */ next = list_first_entry(list, struct page, lru); /* exit on error */ if (err) break; } /* Rotate any leftover pages to the head of the freelist */ if (!list_entry_is_head(next, list, lru) && !list_is_first(&next->lru, list)) list_rotate_to_front(&next->lru, list); spin_unlock_irq(&zone->lock); return err; } static int page_reporting_process_zone(struct page_reporting_dev_info *prdev, struct scatterlist *sgl, struct zone *zone) { unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY; unsigned long watermark; int err = 0; /* Generate minimum watermark to be able to guarantee progress */ watermark = low_wmark_pages(zone) + (PAGE_REPORTING_CAPACITY << PAGE_REPORTING_MIN_ORDER); /* * Cancel request if insufficient free memory or if we failed * to allocate page reporting statistics for the zone. */ if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA)) return err; /* Process each free list starting from lowest order/mt */ for (order = PAGE_REPORTING_MIN_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)) continue; err = page_reporting_cycle(prdev, zone, order, mt, sgl, &offset); if (err) return err; } } /* report the leftover pages before going idle */ leftover = PAGE_REPORTING_CAPACITY - offset; if (leftover) { sgl = &sgl[offset]; err = prdev->report(prdev, sgl, leftover); /* flush any remaining pages out from the last report */ spin_lock_irq(&zone->lock); page_reporting_drain(prdev, sgl, leftover, !err); spin_unlock_irq(&zone->lock); } return err; } static void page_reporting_process(struct work_struct *work) { struct delayed_work *d_work = to_delayed_work(work); struct page_reporting_dev_info *prdev = container_of(d_work, struct page_reporting_dev_info, work); int err = 0, state = PAGE_REPORTING_ACTIVE; struct scatterlist *sgl; struct zone *zone; /* * Change the state to "Active" so that we can track if there is * anyone requests page reporting after we complete our pass. If * the state is not altered by the end of the pass we will switch * to idle and quit scheduling reporting runs. */ atomic_set(&prdev->state, state); /* allocate scatterlist to store pages being reported on */ sgl = kmalloc_array(PAGE_REPORTING_CAPACITY, sizeof(*sgl), GFP_KERNEL); if (!sgl) goto err_out; sg_init_table(sgl, PAGE_REPORTING_CAPACITY); for_each_zone(zone) { err = page_reporting_process_zone(prdev, sgl, zone); if (err) break; } kfree(sgl); err_out: /* * If the state has reverted back to requested then there may be * additional pages to be processed. We will defer for 2s to allow * more pages to accumulate. */ state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE); if (state == PAGE_REPORTING_REQUESTED) schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY); } static DEFINE_MUTEX(page_reporting_mutex); DEFINE_STATIC_KEY_FALSE(page_reporting_enabled); int page_reporting_register(struct page_reporting_dev_info *prdev) { int err = 0; mutex_lock(&page_reporting_mutex); /* nothing to do if already in use */ if (rcu_access_pointer(pr_dev_info)) { err = -EBUSY; goto err_out; } /* initialize state and work structures */ atomic_set(&prdev->state, PAGE_REPORTING_IDLE); INIT_DELAYED_WORK(&prdev->work, &page_reporting_process); /* Begin initial flush of zones */ __page_reporting_request(prdev); /* Assign device to allow notifications */ rcu_assign_pointer(pr_dev_info, prdev); /* enable page reporting notification */ if (!static_key_enabled(&page_reporting_enabled)) { static_branch_enable(&page_reporting_enabled); pr_info("Free page reporting enabled\n"); } err_out: mutex_unlock(&page_reporting_mutex); return err; } EXPORT_SYMBOL_GPL(page_reporting_register); void page_reporting_unregister(struct page_reporting_dev_info *prdev) { mutex_lock(&page_reporting_mutex); if (rcu_access_pointer(pr_dev_info) == prdev) { /* Disable page reporting notification */ RCU_INIT_POINTER(pr_dev_info, NULL); synchronize_rcu(); /* Flush any existing work, and lock it out */ cancel_delayed_work_sync(&prdev->work); } mutex_unlock(&page_reporting_mutex); } EXPORT_SYMBOL_GPL(page_reporting_unregister);