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Subject[PATCH 23/27] mm: numa: Scan pages with elevated page_mapcount
Date
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>
---
include/linux/migrate.h | 7 ++++---
mm/huge_memory.c | 5 +----
mm/memory.c | 7 ++-----
mm/migrate.c | 17 ++++++-----------
mm/mprotect.c | 4 +---
5 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index a405d3dc..e7e26af 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -92,11 +92,12 @@ 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 52c4706..a6153eb 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1478,12 +1478,9 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
ret = HPAGE_PMD_NR;
BUG_ON(pmd_write(entry));
} else {
- struct page *page = pmd_page(*pmd);
ret = 1;

- /* only check non-shared pages */
- if (page_mapcount(page) == 1 &&
- !pmd_numa(*pmd)) {
+ if (!pmd_numa(*pmd)) {
entry = pmdp_get_and_clear(mm, addr, pmd);
entry = pmd_mknuma(entry);
ret = HPAGE_PMD_NR;
diff --git a/mm/memory.c b/mm/memory.c
index 7170707..0e7010c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3579,7 +3579,7 @@ 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;

@@ -3644,16 +3644,13 @@ 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 6f0c244..08ac3ba 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1596,7 +1596,8 @@ 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;
@@ -1604,10 +1605,11 @@ 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;

/*
@@ -1658,13 +1660,6 @@ 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 8e7e9bd..df64356 100644
--- 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;
}
--
1.8.1.4


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