mm, page_owner: track and print last migrate reason

During migration, page_owner info is now copied with the rest of the
page, so the stacktrace leading to free page allocation during migration
is overwritten.  For debugging purposes, it might be however useful to
know that the page has been migrated since its initial allocation.  This
might happen many times during the lifetime for different reasons and
fully tracking this, especially with stacktraces would incur extra
memory costs.  As a compromise, store and print the migrate_reason of
the last migration that occurred to the page.  This is enough to
distinguish compaction, numa balancing etc.

Example page_owner entry after the patch:

  Page allocated via order 0, mask 0x24200ca(GFP_HIGHUSER_MOVABLE)
  PFN 628753 type Movable Block 1228 type Movable Flags 0x1fffff80040030(dirty|lru|swapbacked)
   [<ffffffff811682c4>] __alloc_pages_nodemask+0x134/0x230
   [<ffffffff811b6325>] alloc_pages_vma+0xb5/0x250
   [<ffffffff81177491>] shmem_alloc_page+0x61/0x90
   [<ffffffff8117a438>] shmem_getpage_gfp+0x678/0x960
   [<ffffffff8117c2b9>] shmem_fallocate+0x329/0x440
   [<ffffffff811de600>] vfs_fallocate+0x140/0x230
   [<ffffffff811df434>] SyS_fallocate+0x44/0x70
   [<ffffffff8158cc2e>] entry_SYSCALL_64_fastpath+0x12/0x71
  Page has been migrated, last migrate reason: compaction

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 15 insertions, 1 deletions

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index cac1c0904d5f..9b50325e4ddf 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -23,9 +23,13 @@ enum migrate_reason {
 	MR_SYSCALL,		/* also applies to cpusets */
 	MR_MEMPOLICY_MBIND,
 	MR_NUMA_MISPLACED,
-	MR_CMA
+	MR_CMA,
+	MR_TYPES
 };
 
+/* In mm/debug.c; also keep sync with include/trace/events/migrate.h */
+extern char *migrate_reason_names[MR_TYPES];
+
 #ifdef CONFIG_MIGRATION
 
 extern void putback_movable_pages(struct list_head *l);
diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index 17f118a82854..e1fe7cf5bddf 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -45,6 +45,7 @@ struct page_ext {
 	unsigned int order;
 	gfp_t gfp_mask;
 	unsigned int nr_entries;
+	int last_migrate_reason;
 	unsigned long trace_entries[8];
 #endif
 };
diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
index 6440daab4ef8..555893bf13d7 100644
--- a/include/linux/page_owner.h
+++ b/include/linux/page_owner.h
@@ -12,6 +12,7 @@ extern void __set_page_owner(struct page *page,
 			unsigned int order, gfp_t gfp_mask);
 extern gfp_t __get_page_owner_gfp(struct page *page);
 extern void __copy_page_owner(struct page *oldpage, struct page *newpage);
+extern void __set_page_owner_migrate_reason(struct page *page, int reason);
 
 static inline void reset_page_owner(struct page *page, unsigned int order)
 {
@@ -38,6 +39,11 @@ static inline void copy_page_owner(struct page *oldpage, struct page *newpage)
 	if (static_branch_unlikely(&page_owner_inited))
 		__copy_page_owner(oldpage, newpage);
 }
+static inline void set_page_owner_migrate_reason(struct page *page, int reason)
+{
+	if (static_branch_unlikely(&page_owner_inited))
+		__set_page_owner_migrate_reason(page, reason);
+}
 #else
 static inline void reset_page_owner(struct page *page, unsigned int order)
 {
@@ -53,5 +59,8 @@ static inline gfp_t get_page_owner_gfp(struct page *page)
 static inline void copy_page_owner(struct page *oldpage, struct page *newpage)
 {
 }
+static inline void set_page_owner_migrate_reason(struct page *page, int reason)
+{
+}
 #endif /* CONFIG_PAGE_OWNER */
 #endif /* __LINUX_PAGE_OWNER_H */