[RFC/PATCH 4/6] memcg: shmem reclaim helper

[KAMEZAWA Hiroyuki]

A new call, mem_cgroup_shrink_usage() is added for shmem handling
and removing not usual 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.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

---
 mm/memcontrol.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Index: linux-2.6.26-rc2/mm/memcontrol.c
===================================================================
--- linux-2.6.26-rc2.orig/mm/memcontrol.c
+++ linux-2.6.26-rc2/mm/memcontrol.c
@@ -783,6 +783,30 @@ static void mem_cgroup_drop_all_pages(st
 }
 
 /*
+ * 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();
+
+	while(!progress && --retry) {
+		progress = try_to_free_mem_cgroup_pages(mem, gfp_mask);
+	}
+	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.
  */
Index: linux-2.6.26-rc2/mm/shmem.c
===================================================================
--- linux-2.6.26-rc2.orig/mm/shmem.c
+++ linux-2.6.26-rc2/mm/shmem.c
@@ -1314,13 +1314,12 @@ repeat:
 			unlock_page(swappage);
 			if (error == -ENOMEM) {
 				/* allow reclaim from this memory cgroup */
-				error = mem_cgroup_cache_charge(swappage,
-					current->mm, gfp & ~__GFP_HIGHMEM);
+				error = mem_cgroup_shrink_usage(current->mm,
+					gfp & ~__GFP_HIGHMEM);
 				if (error) {
 					page_cache_release(swappage);
 					goto failed;
 				}
-				mem_cgroup_uncharge_cache_page(swappage);
 			}
 			page_cache_release(swappage);
 			goto repeat;

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