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Subject[PATCH v2 3/4] mm: add find_alloc_contig_pages() interface
Date
find_alloc_contig_pages() is a new interface that attempts to locate
and allocate a contiguous range of pages. It is provided as a more
convenient interface than alloc_contig_range() which is currently
used by CMA and gigantic huge pages.

When attempting to allocate a range of pages, migration is employed
if possible. There is no guarantee that the routine will succeed.
So, the user must be prepared for failure and have a fall back plan.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
include/linux/gfp.h | 12 +++++
mm/page_alloc.c | 136 +++++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 146 insertions(+), 2 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 86a0d06463ab..b0d11777d487 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -573,6 +573,18 @@ static inline bool pm_suspended_storage(void)
extern int alloc_contig_range(unsigned long start, unsigned long end,
unsigned migratetype, gfp_t gfp_mask);
extern void free_contig_range(unsigned long pfn, unsigned long nr_pages);
+extern struct page *find_alloc_contig_pages(unsigned long nr_pages, gfp_t gfp,
+ int nid, nodemask_t *nodemask);
+extern void free_contig_pages(struct page *page, unsigned long nr_pages);
+#else
+static inline struct page *find_alloc_contig_pages(unsigned long nr_pages,
+ gfp_t gfp, int nid, nodemask_t *nodemask)
+{
+ return NULL;
+}
+static inline void free_contig_pages(struct page *page, unsigned long nr_pages)
+{
+}
#endif

#ifdef CONFIG_CMA
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cb1a5e0be6ee..d0a2d0da9eae 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -67,6 +67,7 @@
#include <linux/ftrace.h>
#include <linux/lockdep.h>
#include <linux/nmi.h>
+#include <linux/mmzone.h>

#include <asm/sections.h>
#include <asm/tlbflush.h>
@@ -7913,8 +7914,12 @@ int alloc_contig_range(unsigned long start, unsigned long end,

/* Make sure the range is really isolated. */
if (test_pages_isolated(outer_start, end, false)) {
- pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n",
- __func__, outer_start, end);
+#ifdef MIGRATE_CMA
+ /* Only print messages for CMA allocations */
+ if (migratetype == MIGRATE_CMA)
+ pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n",
+ __func__, outer_start, end);
+#endif
ret = -EBUSY;
goto done;
}
@@ -7950,6 +7955,133 @@ void free_contig_range(unsigned long pfn, unsigned long nr_pages)
}
WARN(count != 0, "%ld pages are still in use!\n", count);
}
+
+/*
+ * Only check for obvious pfn/pages which can not be used/migrated. The
+ * migration code will do the final check. Under stress, this minimal set
+ * has been observed to provide the best results. The checks can be expanded
+ * if needed.
+ */
+static bool contig_pfn_range_valid(struct zone *z, unsigned long start_pfn,
+ unsigned long nr_pages)
+{
+ unsigned long i, end_pfn = start_pfn + nr_pages;
+ struct page *page;
+
+ for (i = start_pfn; i < end_pfn; i++) {
+ if (!pfn_valid(i))
+ return false;
+
+ page = pfn_to_online_page(i);
+
+ if (page_zone(page) != z)
+ return false;
+
+ }
+
+ return true;
+}
+
+/*
+ * Search for and attempt to allocate contiguous allocations greater than
+ * MAX_ORDER.
+ */
+static struct page *__alloc_contig_pages_nodemask(gfp_t gfp,
+ unsigned long order,
+ int nid, nodemask_t *nodemask)
+{
+ unsigned long nr_pages, pfn, flags;
+ struct page *ret_page = NULL;
+ struct zonelist *zonelist;
+ struct zoneref *z;
+ struct zone *zone;
+ int rc;
+
+ nr_pages = 1 << order;
+ zonelist = node_zonelist(nid, gfp);
+ for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp),
+ nodemask) {
+ pgdat_resize_lock(zone->zone_pgdat, &flags);
+ pfn = ALIGN(zone->zone_start_pfn, nr_pages);
+ while (zone_spans_pfn(zone, pfn + nr_pages - 1)) {
+ if (contig_pfn_range_valid(zone, pfn, nr_pages)) {
+ struct page *page = pfn_to_online_page(pfn);
+ unsigned int migratetype;
+
+ /*
+ * All pageblocks in range must be of same
+ * migrate type.
+ */
+ migratetype = get_pageblock_migratetype(page);
+ pgdat_resize_unlock(zone->zone_pgdat, &flags);
+
+ rc = alloc_contig_range(pfn, pfn + nr_pages,
+ migratetype, gfp);
+ if (!rc) {
+ ret_page = pfn_to_page(pfn);
+ return ret_page;
+ }
+ pgdat_resize_lock(zone->zone_pgdat, &flags);
+ }
+ pfn += nr_pages;
+ }
+ pgdat_resize_unlock(zone->zone_pgdat, &flags);
+ }
+
+ return ret_page;
+}
+
+/**
+ * find_alloc_contig_pages() -- attempt to find and allocate a contiguous
+ * range of pages
+ * @nr_pages: number of pages to find/allocate
+ * @gfp: gfp mask used to limit search as well as during compaction
+ * @nid: target node
+ * @nodemask: mask of other possible nodes
+ *
+ * Pages can be freed with a call to free_contig_pages(), or by manually
+ * calling __free_page() for each page allocated.
+ *
+ * Return: pointer to 'order' pages on success, or NULL if not successful.
+ */
+struct page *find_alloc_contig_pages(unsigned long nr_pages, gfp_t gfp,
+ int nid, nodemask_t *nodemask)
+{
+ unsigned long i, alloc_order, order_pages;
+ struct page *pages;
+
+ /*
+ * Underlying allocators perform page order sized allocations.
+ */
+ alloc_order = get_count_order(nr_pages);
+ if (alloc_order < MAX_ORDER) {
+ pages = __alloc_pages_nodemask(gfp, (unsigned int)alloc_order,
+ nid, nodemask);
+ split_page(pages, alloc_order);
+ } else {
+ pages = __alloc_contig_pages_nodemask(gfp, alloc_order, nid,
+ nodemask);
+ }
+
+ if (pages) {
+ /*
+ * More pages than desired could have been allocated due to
+ * rounding up to next page order. Free any excess pages.
+ */
+ order_pages = 1UL << alloc_order;
+ for (i = nr_pages; i < order_pages; i++)
+ __free_page(pages + i);
+ }
+
+ return pages;
+}
+EXPORT_SYMBOL_GPL(find_alloc_contig_pages);
+
+void free_contig_pages(struct page *page, unsigned long nr_pages)
+{
+ free_contig_range(page_to_pfn(page), nr_pages);
+}
+EXPORT_SYMBOL_GPL(free_contig_pages);
#endif

#if defined CONFIG_MEMORY_HOTPLUG || defined CONFIG_CMA
--
2.13.6
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