@@ -163,6 +163,9 @@ enum pageflags {
/* non-lru isolated movable page */
PG_isolated = PG_reclaim,
+
+ /* Only valid for buddy pages. Used to track pages that are reported */
+ PG_reported = PG_uptodate,
};
#ifndef __GENERATING_BOUNDS_H
@@ -432,6 +435,14 @@ static inline bool set_hwpoison_free_buddy_page(struct page *page)
#endif
/*
+ * PageReported() is used to track reported free pages within the Buddy
+ * allocator. We can use the non-atomic version of the test and set
+ * operations as both should be shielded with the zone lock to prevent
+ * any possible races on the setting or clearing of the bit.
+ */
+__PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
+
+/*
* On an anonymous page mapped into a user virtual memory area,
* page->mapping points to its anon_vma, not to a struct address_space;
* with the PAGE_MAPPING_ANON bit set to distinguish it. See rmap.h.
new file mode 100644
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PAGE_REPORTING_H
+#define _LINUX_PAGE_REPORTING_H
+
+#include <linux/mmzone.h>
+#include <linux/scatterlist.h>
+
+#define PAGE_REPORTING_CAPACITY 32
+
+struct page_reporting_dev_info {
+ /* function that alters pages to make them "reported" */
+ int (*report)(struct page_reporting_dev_info *prdev,
+ struct scatterlist *sg, unsigned int nents);
+
+ /* work struct for processing reports */
+ struct delayed_work work;
+
+ /* Current state of page reporting */
+ atomic_t state;
+};
+
+/* Tear-down and bring-up for page reporting devices */
+void page_reporting_unregister(struct page_reporting_dev_info *prdev);
+int page_reporting_register(struct page_reporting_dev_info *prdev);
+#endif /*_LINUX_PAGE_REPORTING_H */
@@ -237,6 +237,17 @@ config COMPACTION
linux-mm@kvack.org.
#
+# support for free page reporting
+config PAGE_REPORTING
+ bool "Free page reporting"
+ def_bool n
+ help
+ Free page reporting allows for the incremental acquisition of
+ free pages from the buddy allocator for the purpose of reporting
+ those pages to another entity, such as a hypervisor, so that the
+ memory can be freed within the host for other uses.
+
+#
# support for page migration
#
config MIGRATION
@@ -118,3 +118,4 @@ obj-$(CONFIG_HMM_MIRROR) += hmm.o
obj-$(CONFIG_MEMFD_CREATE) += memfd.o
obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o
obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
+obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
@@ -74,6 +74,7 @@
#include <asm/div64.h>
#include "internal.h"
#include "shuffle.h"
+#include "page_reporting.h"
/* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
static DEFINE_MUTEX(pcp_batch_high_lock);
@@ -902,6 +903,10 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
static inline void del_page_from_free_list(struct page *page, struct zone *zone,
unsigned int order)
{
+ /* clear reported state and update reported page count */
+ if (page_reported(page))
+ __ClearPageReported(page);
+
list_del(&page->lru);
__ClearPageBuddy(page);
set_page_private(page, 0);
@@ -965,7 +970,7 @@ static inline void del_page_from_free_list(struct page *page, struct zone *zone,
static inline void __free_one_page(struct page *page,
unsigned long pfn,
struct zone *zone, unsigned int order,
- int migratetype)
+ int migratetype, bool report)
{
struct capture_control *capc = task_capc(zone);
unsigned long uninitialized_var(buddy_pfn);
@@ -1050,6 +1055,10 @@ static inline void __free_one_page(struct page *page,
add_to_free_list_tail(page, zone, order, migratetype);
else
add_to_free_list(page, zone, order, migratetype);
+
+ /* Notify page reporting subsystem of freed page */
+ if (report)
+ page_reporting_notify_free(order);
}
/*
@@ -1366,7 +1375,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
if (unlikely(isolated_pageblocks))
mt = get_pageblock_migratetype(page);
- __free_one_page(page, page_to_pfn(page), zone, 0, mt);
+ __free_one_page(page, page_to_pfn(page), zone, 0, mt, true);
trace_mm_page_pcpu_drain(page, 0, mt);
}
spin_unlock(&zone->lock);
@@ -1382,7 +1391,7 @@ static void free_one_page(struct zone *zone,
is_migrate_isolate(migratetype))) {
migratetype = get_pfnblock_migratetype(page, pfn);
}
- __free_one_page(page, pfn, zone, order, migratetype);
+ __free_one_page(page, pfn, zone, order, migratetype, true);
spin_unlock(&zone->lock);
}
@@ -3233,7 +3242,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
lockdep_assert_held(&zone->lock);
/* Return isolated page to tail of freelist. */
- __free_one_page(page, page_to_pfn(page), zone, order, mt);
+ __free_one_page(page, page_to_pfn(page), zone, order, mt, false);
}
/*
new file mode 100644
@@ -0,0 +1,319 @@
+// 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) && page_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;
+ 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);
+
+ /* 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;
+
+ /* Attempt to pull page from list */
+ if (!__isolate_free_page(page, order))
+ break;
+
+ /* Add page to scatter list */
+ --(*offset);
+ sg_set_page(&sgl[*offset], page, page_len, 0);
+
+ /* If scatterlist isn't full grab more pages */
+ if (*offset)
+ continue;
+
+ /* 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;
+
+ /* 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;
+ }
+
+ 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);
new file mode 100644
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _MM_PAGE_REPORTING_H
+#define _MM_PAGE_REPORTING_H
+
+#include <linux/mmzone.h>
+#include <linux/pageblock-flags.h>
+#include <linux/page-isolation.h>
+#include <linux/jump_label.h>
+#include <linux/slab.h>
+#include <asm/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);
+
+static inline bool page_reported(struct page *page)
+{
+ return static_branch_unlikely(&page_reporting_enabled) &&
+ PageReported(page);
+}
+
+/**
+ * page_reporting_notify_free - Free page notification to start page processing
+ *
+ * This function is meant to act as a screener for __page_reporting_notify
+ * which will determine if a give zone has crossed over the high-water mark
+ * that will justify us beginning page treatment. If we have crossed that
+ * threshold then it will start the process of pulling some pages and
+ * placing them in the batch list for treatment.
+ */
+static inline void page_reporting_notify_free(unsigned int order)
+{
+ /* Called from hot path in __free_one_page() */
+ 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();
+}
+#else /* CONFIG_PAGE_REPORTING */
+#define page_reported(_page) false
+
+static inline void page_reporting_notify_free(unsigned int order)
+{
+}
+#endif /* CONFIG_PAGE_REPORTING */
+#endif /*_MM_PAGE_REPORTING_H */