memcg: helper function for relcaim from shmem.

A new call, mem_cgroup_shrink_usage() is added for shmem handling and
relacing non-standard usage of mem_cgroup_charge/uncharge.

Now, shmem calls mem_cgroup_charge() just for reclaim some pages from
mem_cgroup.  In general, shmem is used by some process group and not for
global resource (like file caches).  So, it's reasonable to reclaim pages
from mem_cgroup where shmem is mainly used.

[hugh@veritas.com: shmem_getpage release page sooner]
[hugh@veritas.com: mem_cgroup_shrink_usage css_put]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 37 insertions, 7 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index b4980b8f048e..fdf3967e1397 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -37,6 +37,8 @@ extern int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 extern void mem_cgroup_uncharge_page(struct page *page);
 extern void mem_cgroup_uncharge_cache_page(struct page *page);
 extern void mem_cgroup_move_lists(struct page *page, bool active);
+extern int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask);
+
 extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
                                         struct list_head *dst,
                                         unsigned long *scanned, int order,
@@ -102,6 +104,11 @@ static inline void mem_cgroup_uncharge_cache_page(struct page *page)
 {
 }
 
+static inline int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask)
+{
+        return 0;
+}
+
 static inline void mem_cgroup_move_lists(struct page *page, bool active)
 {
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a61706193c31..f46b8615de6c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -781,6 +781,32 @@ void mem_cgroup_end_migration(struct page *newpage)
 }
 
 /*
+ * A call to try to shrink memory usage under specified resource controller.
+ * This is typically used for page reclaiming for shmem for reducing side
+ * effect of page allocation from shmem, which is used by some mem_cgroup.
+ */
+int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask)
+{
+        struct mem_cgroup *mem;
+        int progress = 0;
+        int retry = MEM_CGROUP_RECLAIM_RETRIES;
+
+        rcu_read_lock();
+        mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
+        css_get(&mem->css);
+        rcu_read_unlock();
+
+        do {
+                progress = try_to_free_mem_cgroup_pages(mem, gfp_mask);
+        } while (!progress && --retry);
+
+        css_put(&mem->css);
+        if (!retry)
+                return -ENOMEM;
+        return 0;
+}
+
+/*
  * This routine traverse page_cgroup in given list and drop them all.
  * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
  */
diff --git a/mm/shmem.c b/mm/shmem.c
index d58305e8a484..f92fea94d037 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1315,17 +1315,14 @@ repeat:
                         shmem_swp_unmap(entry);
                         spin_unlock(&info->lock);
                         unlock_page(swappage);
+                        page_cache_release(swappage);
                         if (error == -ENOMEM) {
                                 /* allow reclaim from this memory cgroup */
-                                error = mem_cgroup_cache_charge(swappage,
-                                        current->mm, gfp & ~__GFP_HIGHMEM);
-                                if (error) {
-                                        page_cache_release(swappage);
+                                error = mem_cgroup_shrink_usage(current->mm,
+                                                                gfp);
+                                if (error)
                                         goto failed;
-                                }
-                                mem_cgroup_uncharge_cache_page(swappage);
                         }
-                        page_cache_release(swappage);
                         goto repeat;
                 }
         } else if (sgp == SGP_READ && !filepage) {