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Commit 1bc115d8 authored by Mel Gorman's avatar Mel Gorman Committed by Ingo Molnar
Browse files

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: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarRik 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: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-28-git-send-email-mgorman@suse.de


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 9ff1d9ff

include/linux/migrate.h

+4 −3
Original line number Diff line number Diff line
@@ -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 */

}

mm/huge_memory.c

+5 −7
Original line number Diff line number Diff line
@@ -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);

mm/memory.c

+2 −5
Original line number Diff line number Diff line
@@ -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 {

mm/migrate.c

+6 −11
Original line number Diff line number Diff line
@@ -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

mm/mprotect.c

+1 −3
Original line number Diff line number Diff line
@@ -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;

					}