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, 35 insertions, 3 deletions

diff --git a/mm/debug.c b/mm/debug.c
index 231e1452a912..78dc54877075 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -10,9 +10,20 @@
 #include <linux/trace_events.h>
 #include <linux/memcontrol.h>
 #include <trace/events/mmflags.h>
+#include <linux/migrate.h>
 
 #include "internal.h"
 
+char *migrate_reason_names[MR_TYPES] = {
+        "compaction",
+        "memory_failure",
+        "memory_hotplug",
+        "syscall_or_cpuset",
+        "mempolicy_mbind",
+        "numa_misplaced",
+        "cma",
+};
+
 const struct trace_print_flags pageflag_names[] = {
         __def_pageflag_names,
         {0, NULL}
diff --git a/mm/migrate.c b/mm/migrate.c
index 8133805431ba..432ecd0172cd 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -955,8 +955,10 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
         }
 
         rc = __unmap_and_move(page, newpage, force, mode);
-        if (rc == MIGRATEPAGE_SUCCESS)
+        if (rc == MIGRATEPAGE_SUCCESS) {
                 put_new_page = NULL;
+                set_page_owner_migrate_reason(newpage, reason);
+        }
 
 out:
         if (rc != -EAGAIN) {
@@ -1021,7 +1023,7 @@ out:
 static int unmap_and_move_huge_page(new_page_t get_new_page,
                                 free_page_t put_new_page, unsigned long private,
                                 struct page *hpage, int force,
-                                enum migrate_mode mode)
+                                enum migrate_mode mode, int reason)
 {
         int rc = -EAGAIN;
         int *result = NULL;
@@ -1079,6 +1081,7 @@ put_anon:
         if (rc == MIGRATEPAGE_SUCCESS) {
                 hugetlb_cgroup_migrate(hpage, new_hpage);
                 put_new_page = NULL;
+                set_page_owner_migrate_reason(new_hpage, reason);
         }
 
         unlock_page(hpage);
@@ -1151,7 +1154,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
                         if (PageHuge(page))
                                 rc = unmap_and_move_huge_page(get_new_page,
                                                 put_new_page, private, page,
-                                                pass > 2, mode);
+                                                pass > 2, mode, reason);
                         else
                                 rc = unmap_and_move(get_new_page, put_new_page,
                                                 private, page, pass > 2, mode,
@@ -1842,6 +1845,7 @@ fail_putback:
         set_page_memcg(new_page, page_memcg(page));
         set_page_memcg(page, NULL);
         page_remove_rmap(page, true);
+        set_page_owner_migrate_reason(new_page, MR_NUMA_MISPLACED);
 
         spin_unlock(ptl);
         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 774b55623212..a57068cfe52f 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -6,6 +6,7 @@
 #include <linux/stacktrace.h>
 #include <linux/page_owner.h>
 #include <linux/jump_label.h>
+#include <linux/migrate.h>
 #include "internal.h"
 
 static bool page_owner_disabled = true;
@@ -73,10 +74,18 @@ void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
         page_ext->order = order;
         page_ext->gfp_mask = gfp_mask;
         page_ext->nr_entries = trace.nr_entries;
+        page_ext->last_migrate_reason = -1;
 
         __set_bit(PAGE_EXT_OWNER, &page_ext->flags);
 }
 
+void __set_page_owner_migrate_reason(struct page *page, int reason)
+{
+        struct page_ext *page_ext = lookup_page_ext(page);
+
+        page_ext->last_migrate_reason = reason;
+}
+
 gfp_t __get_page_owner_gfp(struct page *page)
 {
         struct page_ext *page_ext = lookup_page_ext(page);
@@ -151,6 +160,14 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
         if (ret >= count)
                 goto err;
 
+        if (page_ext->last_migrate_reason != -1) {
+                ret += snprintf(kbuf + ret, count - ret,
+                        "Page has been migrated, last migrate reason: %s\n",
+                        migrate_reason_names[page_ext->last_migrate_reason]);
+                if (ret >= count)
+                        goto err;
+        }
+
         ret += snprintf(kbuf + ret, count - ret, "\n");
         if (ret >= count)
                 goto err;