Re: [PATCH 13/18] mm: numa: Scan pages with elevated page_mapcount
On Wed, Jul 17, 2013 at 01:22:22PM +0800, Sam Ben wrote: > On 07/15/2013 11:20 PM, Mel Gorman wrote: > >Currently automatic NUMA balancing is unable to distinguish between false > >shared versus private pages except by ignoring pages with an elevated > > What's the meaning of false shared? > Two tasks may be operating on a shared buffer that is not aligned. It is expected that will at least cache align to avoid CPU cache line bouncing but the buffers are not necessarily page aligned. A page is the minimum granularity we can track NUMA hinting faults so two tasks sharing such a page will appear to be sharing data when in fact they are not. -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 13/18] mm: numa: Scan pages with elevated page_mapcount
On 07/15/2013 11:20 PM, Mel Gorman wrote:
Currently automatic NUMA balancing is unable to distinguish between false
shared versus private pages except by ignoring pages with an elevated
What's the meaning of false shared?
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
---
include/linux/migrate.h | 7 ---
mm/memory.c | 7 ++-
mm/migrate.c| 17 ++---
mm/mprotect.c | 4 +---
4 files changed, 13 insertions(+), 22 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/memory.c b/mm/memory.c
index ab933be..62ae8a7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3586,7 +3586,7 @@ 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)
current_nid = target_nid;
@@ -3651,9 +3651,6 @@ 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;
/*
* Note that the NUMA fault is later accounted to either
@@ -3671,7 +3668,7 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct
vm_area_struct *vma,
/* Migrate to the requested node */
pte_unmap_unlock(pte, ptl);
- migrated = migrate_misplaced_page(page, target_nid);
+ migrated = migrate_misplaced_page(page, vma, target_nid);
if (migrated)
curr_nid = target_nid;
task_numa_fault(last_nid, curr_nid, 1, migrated);
diff --git a/mm/migrate.c b/mm/migrate.c
index 3bbaf5d..23f8122 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1579,7 +1579,8 @@ 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;
@@ -1587,10 +1588,11 @@ 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;
/*
@@ -1641,13 +1643,6 @@ 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 t
[PATCH 13/18] 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
---
include/linux/migrate.h | 7 ---
mm/memory.c | 7 ++-
mm/migrate.c| 17 ++---
mm/mprotect.c | 4 +---
4 files changed, 13 insertions(+), 22 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/memory.c b/mm/memory.c
index ab933be..62ae8a7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3586,7 +3586,7 @@ 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)
current_nid = target_nid;
@@ -3651,9 +3651,6 @@ 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;
/*
* Note that the NUMA fault is later accounted to either
@@ -3671,7 +3668,7 @@ static int do_pmd_numa_page(struct mm_struct *mm, struct
vm_area_struct *vma,
/* Migrate to the requested node */
pte_unmap_unlock(pte, ptl);
- migrated = migrate_misplaced_page(page, target_nid);
+ migrated = migrate_misplaced_page(page, vma, target_nid);
if (migrated)
curr_nid = target_nid;
task_numa_fault(last_nid, curr_nid, 1, migrated);
diff --git a/mm/migrate.c b/mm/migrate.c
index 3bbaf5d..23f8122 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1579,7 +1579,8 @@ 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;
@@ -1587,10 +1588,11 @@ 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;
/*
@@ -1641,13 +1643,6 @@ 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 go
