mm: migrate: do not touch page->mem_cgroup of live pages

Changing a page's memcg association complicates dealing with the page,
so we want to limit this as much as possible.  Page migration e.g.  does
not have to do that.  Just like page cache replacement, it can forcibly
charge a replacement page, and then uncharge the old page when it gets
freed.  Temporarily overcharging the cgroup by a single page is not an
issue in practice, and charging is so cheap nowadays that this is much
preferrable to the headache of messing with live pages.

The only place that still changes the page->mem_cgroup binding of live
pages is when pages move along with a task to another cgroup.  But that
path isolates the page from the LRU, takes the page lock, and the move
lock (lock_page_memcg()).  That means page->mem_cgroup is always stable
in callers that have the page isolated from the LRU or locked.  Lighter
unlocked paths, like writeback accounting, can use lock_page_memcg().

[akpm@linux-foundation.org: fix build]
[vdavydov@virtuozzo.com: fix lockdep splat]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 09b44984936931a2d84d4ab9477819f919c8a19f..c45ab3fb6e04d1af8ecf4f9291209256b92188a8 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -300,7 +300,7 @@ void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg,
 void mem_cgroup_uncharge(struct page *page);
 void mem_cgroup_uncharge_list(struct list_head *page_list);
 
-void mem_cgroup_replace_page(struct page *oldpage, struct page *newpage);
+void mem_cgroup_migrate(struct page *oldpage, struct page *newpage);
 
 struct lruvec *mem_cgroup_zone_lruvec(struct zone *, struct mem_cgroup *);
 struct lruvec *mem_cgroup_page_lruvec(struct page *, struct zone *);
@@ -580,7 +580,7 @@ static inline void mem_cgroup_uncharge_list(struct list_head *page_list)
 {
 }
 
-static inline void mem_cgroup_replace_page(struct page *old, struct page *new)
+static inline void mem_cgroup_migrate(struct page *old, struct page *new)
 {
 }
 

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b97243d6aa498ba5979f66fcc6789d23d41dcfe6..6b471d1fc8df45c17356872e0bf6abf885b77d28 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -905,20 +905,11 @@ static inline struct mem_cgroup *page_memcg(struct page *page)
 {
        return page->mem_cgroup;
 }
-
-static inline void set_page_memcg(struct page *page, struct mem_cgroup *memcg)
-{
-       page->mem_cgroup = memcg;
-}
 #else
 static inline struct mem_cgroup *page_memcg(struct page *page)
 {
        return NULL;
 }
-
-static inline void set_page_memcg(struct page *page, struct mem_cgroup *memcg)
-{
-}
 #endif
 
 /*

diff --git a/mm/filemap.c b/mm/filemap.c
index ee8140cf935d4a8208e91d644c6b7e71f777d3ec..d8317caffe85128af4fa3aa26f8e9bdca25f8e93 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -577,7 +577,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
                        __inc_zone_page_state(new, NR_SHMEM);
                spin_unlock_irqrestore(&mapping->tree_lock, flags);
                unlock_page_memcg(memcg);
-               mem_cgroup_replace_page(old, new);
+               mem_cgroup_migrate(old, new);
                radix_tree_preload_end();
                if (freepage)
                        freepage(old);

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 864e237f32d9ae38874739d439a9f6a825e14489..64506b2eef3479dc190ec93f48f2852e32a7b7cf 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4457,7 +4457,7 @@ static int mem_cgroup_move_account(struct page *page,
        VM_BUG_ON(compound && !PageTransHuge(page));
 
        /*
-        * Prevent mem_cgroup_replace_page() from looking at
+        * Prevent mem_cgroup_migrate() from looking at
         * page->mem_cgroup of its source page while we change it.
         */
        ret = -EBUSY;
@@ -5486,16 +5486,17 @@ void mem_cgroup_uncharge_list(struct list_head *page_list)
 }
 
 /**
- * mem_cgroup_replace_page - migrate a charge to another page
- * @oldpage: currently charged page
- * @newpage: page to transfer the charge to
+ * mem_cgroup_migrate - charge a page's replacement
+ * @oldpage: currently circulating page
+ * @newpage: replacement page
  *
- * Migrate the charge from @oldpage to @newpage.
+ * Charge @newpage as a replacement page for @oldpage. @oldpage will
+ * be uncharged upon free.
  *
  * Both pages must be locked, @newpage->mapping must be set up.
  * Either or both pages might be on the LRU already.
  */
-void mem_cgroup_replace_page(struct page *oldpage, struct page *newpage)
+void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
 {
        struct mem_cgroup *memcg;
        unsigned int nr_pages;

diff --git a/mm/migrate.c b/mm/migrate.c
index 432ecd0172cdf6cc825feacf367b8157cd64fe82..848327d4a7edad7c4bd97dcb7166eebdd0839c69 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -326,12 +326,13 @@ int migrate_page_move_mapping(struct address_space *mapping,
                        return -EAGAIN;
 
                /* No turning back from here */
-               set_page_memcg(newpage, page_memcg(page));
                newpage->index = page->index;
                newpage->mapping = page->mapping;
                if (PageSwapBacked(page))
                        SetPageSwapBacked(newpage);
 
+               mem_cgroup_migrate(page, newpage);
+
                return MIGRATEPAGE_SUCCESS;
        }
 
@@ -373,7 +374,6 @@ int migrate_page_move_mapping(struct address_space *mapping,
         * Now we know that no one else is looking at the page:
         * no turning back from here.
         */
-       set_page_memcg(newpage, page_memcg(page));
        newpage->index = page->index;
        newpage->mapping = page->mapping;
        if (PageSwapBacked(page))
@@ -428,6 +428,8 @@ int migrate_page_move_mapping(struct address_space *mapping,
        }
        local_irq_enable();
 
+       mem_cgroup_migrate(page, newpage);
+
        return MIGRATEPAGE_SUCCESS;
 }
 
@@ -458,9 +460,9 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
                return -EAGAIN;
        }
 
-       set_page_memcg(newpage, page_memcg(page));
        newpage->index = page->index;
        newpage->mapping = page->mapping;
+
        get_page(newpage);
 
        radix_tree_replace_slot(pslot, newpage);
@@ -468,6 +470,9 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
        page_unfreeze_refs(page, expected_count - 1);
 
        spin_unlock_irq(&mapping->tree_lock);
+
+       mem_cgroup_migrate(page, newpage);
+
        return MIGRATEPAGE_SUCCESS;
 }
 
@@ -775,7 +780,6 @@ static int move_to_new_page(struct page *newpage, struct page *page,
         * page is freed; but stats require that PageAnon be left as PageAnon.
         */
        if (rc == MIGRATEPAGE_SUCCESS) {
-               set_page_memcg(page, NULL);
                if (!PageAnon(page))
                        page->mapping = NULL;
        }
@@ -1842,8 +1846,7 @@ fail_putback:
        }
 
        mlock_migrate_page(new_page, page);
-       set_page_memcg(new_page, page_memcg(page));
-       set_page_memcg(page, NULL);
+       mem_cgroup_migrate(page, new_page);
        page_remove_rmap(page, true);
        set_page_owner_migrate_reason(new_page, MR_NUMA_MISPLACED);
 

diff --git a/mm/shmem.c b/mm/shmem.c
index 440e2a7e6c1c2ca706376eb72d719fb8b83af05a..1acfdbc4bd9e306e31a8759aeb46f9d43dfd0113 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1116,7 +1116,7 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp,
                 */
                oldpage = newpage;
        } else {
-               mem_cgroup_replace_page(oldpage, newpage);
+               mem_cgroup_migrate(oldpage, newpage);
                lru_cache_add_anon(newpage);
                *pagep = newpage;
        }