mm: numa: Scan pages with elevated page_mapcount

Currently automatic NUMA balancing is unable to distinguish between false
shared versus private pages except by ignoring pages with an elevated
page_mapcount entirely. This avoids shared pages bouncing between the
nodes whose task is using them but that is ignored quite a lot of data.

This patch kicks away the training wheels in preparation for adding support
for identifying shared/private pages is now in place. The ordering is so
that the impact of the shared/private detection can be easily measured. Note
that the patch does not migrate shared, file-backed within vmas marked
VM_EXEC as these are generally shared library pages. Migrating such pages
is not beneficial as there is an expectation they are read-shared between
caches and iTLB and iCache pressure is generally low.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-28-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 8d3c57f..f5096b5 100644 (file)
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -90,11 +90,12 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
 #endif /* CONFIG_MIGRATION */
 
 #ifdef CONFIG_NUMA_BALANCING
-extern int migrate_misplaced_page(struct page *page, int node);
-extern int migrate_misplaced_page(struct page *page, int node);
+extern int migrate_misplaced_page(struct page *page,
+                                 struct vm_area_struct *vma, int node);
 extern bool migrate_ratelimited(int node);
 #else
-static inline int migrate_misplaced_page(struct page *page, int node)
+static inline int migrate_misplaced_page(struct page *page,
+                                        struct vm_area_struct *vma, int node)
 {
        return -EAGAIN; /* can't migrate now */
 }

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9142167..2a28c2c 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1484,14 +1484,12 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
                        struct page *page = pmd_page(*pmd);
 
                        /*
-                        * Only check non-shared pages. Do not trap faults
-                        * against the zero page. The read-only data is likely
-                        * to be read-cached on the local CPU cache and it is
-                        * less useful to know about local vs remote hits on
-                        * the zero page.
+                        * Do not trap faults against the zero page. The
+                        * read-only data is likely to be read-cached on the
+                        * local CPU cache and it is less useful to know about
+                        * local vs remote hits on the zero page.
                         */
-                       if (page_mapcount(page) == 1 &&
-                           !is_huge_zero_page(page) &&
+                       if (!is_huge_zero_page(page) &&
                            !pmd_numa(*pmd)) {
                                entry = pmdp_get_and_clear(mm, addr, pmd);
                                entry = pmd_mknuma(entry);

diff --git a/mm/memory.c b/mm/memory.c
index 24bc9b8..3e3b4b8 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3577,7 +3577,7 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
        }
 
        /* Migrate to the requested node */
-       migrated = migrate_misplaced_page(page, target_nid);
+       migrated = migrate_misplaced_page(page, vma, target_nid);
        if (migrated)
                page_nid = target_nid;
 
@@ -3642,16 +3642,13 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                page = vm_normal_page(vma, addr, pteval);
                if (unlikely(!page))
                        continue;
-               /* only check non-shared pages */
-               if (unlikely(page_mapcount(page) != 1))
-                       continue;
 
                last_nid = page_nid_last(page);
                page_nid = page_to_nid(page);
                target_nid = numa_migrate_prep(page, vma, addr, page_nid);
                pte_unmap_unlock(pte, ptl);
                if (target_nid != -1) {
-                       migrated = migrate_misplaced_page(page, target_nid);
+                       migrated = migrate_misplaced_page(page, vma, target_nid);
                        if (migrated)
                                page_nid = target_nid;
                } else {

diff --git a/mm/migrate.c b/mm/migrate.c
index 7bd90d3..fcba2f4 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1599,7 +1599,8 @@ int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
  * node. Caller is expected to have an elevated reference count on
  * the page that will be dropped by this function before returning.
  */
-int migrate_misplaced_page(struct page *page, int node)
+int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
+                          int node)
 {
        pg_data_t *pgdat = NODE_DATA(node);
        int isolated;
@@ -1607,10 +1608,11 @@ int migrate_misplaced_page(struct page *page, int node)
        LIST_HEAD(migratepages);
 
        /*
-        * Don't migrate pages that are mapped in multiple processes.
-        * TODO: Handle false sharing detection instead of this hammer
+        * Don't migrate file pages that are mapped in multiple processes
+        * with execute permissions as they are probably shared libraries.
         */
-       if (page_mapcount(page) != 1)
+       if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
+           (vma->vm_flags & VM_EXEC))
                goto out;
 
        /*
@@ -1661,13 +1663,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
        int page_lru = page_is_file_cache(page);
 
        /*
-        * Don't migrate pages that are mapped in multiple processes.
-        * TODO: Handle false sharing detection instead of this hammer
-        */
-       if (page_mapcount(page) != 1)
-               goto out_dropref;
-
-       /*
         * Rate-limit the amount of data that is being migrated to a node.
         * Optimal placement is no good if the memory bus is saturated and
         * all the time is being spent migrating!

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 2da33dc..41e0292 100644 (file)
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -69,9 +69,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                                        if (last_nid != this_nid)
                                                all_same_node = false;
 
-                                       /* only check non-shared pages */
-                                       if (!pte_numa(oldpte) &&
-                                           page_mapcount(page) == 1) {
+                                       if (!pte_numa(oldpte)) {
                                                ptent = pte_mknuma(ptent);
                                                updated = true;
                                        }