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mm: numa: Scan pages with elevated page_mapcount

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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>
This commit is contained in:
Mel Gorman 2013-10-07 11:29:05 +01:00 committed by Ingo Molnar
parent 9ff1d9ff3c
commit 1bc115d87d
5 changed files with 18 additions and 29 deletions
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7
include/linux/migrate.h
View file

@ -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 */
}

12
mm/huge_memory.c
View file

@ -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);

7
mm/memory.c
View file

@ -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 {

17
mm/migrate.c
View file

@ -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;
/*
@ -1660,13 +1662,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
struct mem_cgroup *memcg = NULL;
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

4
mm/mprotect.c
View file

@ -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;
}