[RFC PATCH 1/3] zram: charge the compressed RAM to the page's memcgroup

[Zhongkun He]

The compressed RAM is currently charged to kernel, not to
any memory cgroup, which is not satisfy our usage scenario.
if the memory of a task is limited by memcgroup, it will
swap out the memory to zram swap device when the memory
is insufficient. In that case, the memory limit will have
no effect.

So, it should makes sense to charge the compressed RAM to
the page's memory cgroup.

Signed-off-by: Zhongkun He <hezhongkun.hzk@xxxxxxxxxxxxx>
---
 drivers/block/zram/zram_drv.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index f6d90f1ba5cf..03b508447473 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -33,6 +33,7 @@
 #include <linux/debugfs.h>
 #include <linux/cpuhotplug.h>
 #include <linux/part_stat.h>
+#include <linux/memcontrol.h>
 
 #include "zram_drv.h"
 
@@ -1419,6 +1420,10 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	struct zcomp_strm *zstrm;
 	unsigned long element = 0;
 	enum zram_pageflags flags = 0;
+	struct mem_cgroup *memcg, *old_memcg;
+
+	memcg = page_memcg(page);
+	old_memcg = set_active_memcg(memcg);
 
 	mem = kmap_atomic(page);
 	if (page_same_filled(mem, &element)) {
@@ -1426,7 +1431,7 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 		/* Free memory associated with this sector now. */
 		flags = ZRAM_SAME;
 		atomic64_inc(&zram->stats.same_pages);
-		goto out;
+		goto out_free;
 	}
 	kunmap_atomic(mem);
 
@@ -1440,7 +1445,7 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 		pr_err("Compression failed! err=%d\n", ret);
 		zs_free(zram->mem_pool, handle);
-		return ret;
+		goto out;
 	}
 
 	if (comp_len >= huge_class_size)
@@ -1470,8 +1475,10 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 		handle = zs_malloc(zram->mem_pool, comp_len,
 				GFP_NOIO | __GFP_HIGHMEM |
 				__GFP_MOVABLE);
-		if (IS_ERR_VALUE(handle))
-			return PTR_ERR((void *)handle);
+		if (IS_ERR_VALUE(handle)) {
+			ret = PTR_ERR((void *)handle);
+			goto out;
+		}
 
 		if (comp_len != PAGE_SIZE)
 			goto compress_again;
@@ -1491,7 +1498,8 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	if (zram->limit_pages && alloced_pages > zram->limit_pages) {
 		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 		zs_free(zram->mem_pool, handle);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out;
 	}
 
 	dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
@@ -1506,7 +1514,7 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 	zs_unmap_object(zram->mem_pool, handle);
 	atomic64_add(comp_len, &zram->stats.compr_data_size);
-out:
+out_free:
 	/*
 	 * Free memory associated with this sector
 	 * before overwriting unused sectors.
@@ -1531,6 +1539,8 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 
 	/* Update stats */
 	atomic64_inc(&zram->stats.pages_stored);
+out:
+	set_active_memcg(old_memcg);
 	return ret;
 }
 
-- 
2.25.1