[Devel] [RFC][PATCH 3/4] memcg shrink usage at limit change

[KAMEZAWA Hiroyuki]

Shrinking memory usage at limit change.

This is an enhancement. based on res_counter-limit-change-ebusy.patch

Changelog: v3 -> v4
  - core logic is separated into two parts. (reuse the function later.)
  - added cond_resched() again.
    1. I was pointed out that alloc_pages() does cond_resched() after
       try_to_free_pages().
    2. This routine is called by an user. A user can set 'nice' in general.

Changelog: v2 -> v3
  - supported interrupt by signal. (A user can stop limit change by Ctrl-C.)

Changelog: v1 -> v2
  - adjusted to be based on write_string() patch set
  - removed backword goto.
  - removed unneccesary cond_resched().


Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

 Documentation/controllers/memory.txt |    3 -
 mm/memcontrol.c                      |   73 +++++++++++++++++++++++++++++++++--
 2 files changed, 70 insertions(+), 6 deletions(-)

Index: mmtom-stamp-2008-07-15-15-39/mm/memcontrol.c
===================================================================
--- mmtom-stamp-2008-07-15-15-39.orig/mm/memcontrol.c
+++ mmtom-stamp-2008-07-15-15-39/mm/memcontrol.c
@@ -804,6 +804,55 @@ int mem_cgroup_shrink_usage(struct mm_st
 }
 
 /*
+ * Shrink routine works cooperatively with users rather than the kernel.
+ * So,
+ *    - we have to check signals
+ *    - we pass GFP_HIGHUSERMOVABLE.
+ *  TODO?:
+ *     - allow timeout
+ */
+static int mem_cgroup_shrink_usage_to(struct mem_cgroup *memcg,
+		unsigned long long val)
+{
+	int retry_count = MEM_CGROUP_RECLAIM_RETRIES;
+	int progress;
+	int ret;
+
+	while (!res_counter_check_under_val(&memcg->res, val)) {
+		if (signal_pending(current)) {
+			ret = -EINTR;
+			break;
+		}
+		if (!retry_count) {
+			ret = -EBUSY;
+			break;
+		}
+		progress = try_to_free_mem_cgroup_pages(memcg,
+					GFP_HIGHUSER_MOVABLE);
+		if (!progress)
+			retry_count--;
+		cond_resched();
+	}
+	return 0;
+}
+
+int mem_cgroup_resize_limit(struct mem_cgroup *memcg, unsigned long long val)
+{
+	int ret = 0;
+
+	do  {
+		ret = mem_cgroup_shrink_usage_to(memcg, val);
+		if (ret < 0)
+			break;
+		/* memory usage shrinking succeed. */
+		if (res_counter_set_limit(&memcg->res, val))
+			break;
+	} while (1);
+	return ret;
+}
+
+
+/*
  * This routine traverse page_cgroup in given list and drop them all.
  * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
  */
@@ -883,13 +932,29 @@ static u64 mem_cgroup_read(struct cgroup
 	return res_counter_read_u64(&mem_cgroup_from_cont(cont)->res,
 				    cft->private);
 }
-
+/*
+ * The user of this function is...
+ * RES_LIMIT.
+ */
 static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 			    const char *buffer)
 {
-	return res_counter_write(&mem_cgroup_from_cont(cont)->res,
-				 cft->private, buffer,
-				 res_counter_memparse_write_strategy);
+	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
+	unsigned long long val;
+	int ret;
+
+	switch (cft->private) {
+	case RES_LIMIT:
+		/* This function does all necessary parse...reuse it */
+		ret = res_counter_memparse_write_strategy(buffer, &val);
+		if (!ret)
+			ret = mem_cgroup_resize_limit(memcg, val);
+		break;
+	default:
+		ret = -EINVAL; /* should be BUG() ? */
+		break;
+	}
+	return ret;
 }
 
 static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
Index: mmtom-stamp-2008-07-15-15-39/Documentation/controllers/memory.txt
===================================================================
--- mmtom-stamp-2008-07-15-15-39.orig/Documentation/controllers/memory.txt
+++ mmtom-stamp-2008-07-15-15-39/Documentation/controllers/memory.txt
@@ -242,8 +242,7 @@ rmdir() if there are no tasks.
 1. Add support for accounting huge pages (as a separate controller)
 2. Make per-cgroup scanner reclaim not-shared pages first
 3. Teach controller to account for shared-pages
-4. Start reclamation when the limit is lowered
-5. Start reclamation in the background when the limit is
+4. Start reclamation in the background when the limit is
    not yet hit but the usage is getting closer
 
 Summary

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