[PATCH] mm/vmscan.c: drop_slab_node with task's memcg

[Neil Sun]

This patch makes shrink_slab() with task's memcg in drop_slab_node(),
so we can free reclaimable slab objects belongs to memcg /lxc/i-vbe1u8o7
with following command:

cgexec -g memory:/lxc/i-vbe1u8o7 sysctl vm.drop_caches=2

Test with following steps:

root@i-yl0pwrt8:~# free -h
              total        used        free      shared  buff/cache   available
Mem:           62Gi       265Mi        62Gi       1.0Mi       290Mi        61Gi
Swap:          31Gi          0B        31Gi
root@i-yl0pwrt8:~# (cd /tmp && /root/generate_slab_cache)
root@i-yl0pwrt8:~# free -h
              total        used        free      shared  buff/cache   available
Mem:           62Gi       266Mi        60Gi       1.0Mi       2.2Gi        61Gi
Swap:          31Gi          0B        31Gi
root@i-yl0pwrt8:~# cgcreate -g memory:/lxc/i-vbe1u8o7
root@i-yl0pwrt8:~# cgexec -g memory:/lxc/i-vbe1u8o7 /root/generate_slab_cache
root@i-yl0pwrt8:~# free -h
              total        used        free      shared  buff/cache   available
Mem:           62Gi       267Mi        58Gi       1.0Mi       4.1Gi        61Gi
Swap:          31Gi          0B        31Gi
root@i-yl0pwrt8:~# cgexec -g memory:/lxc/i-vbe1u8o7 sysctl vm.drop_caches=2
vm.drop_caches = 2
root@i-yl0pwrt8:~# free -h
              total        used        free      shared  buff/cache   available
Mem:           62Gi       268Mi        60Gi       1.0Mi       2.2Gi        61Gi
Swap:          31Gi          0B        31Gi
root@i-yl0pwrt8:~# sysctl vm.drop_caches=2
vm.drop_caches = 2
root@i-yl0pwrt8:~# free -h
              total        used        free      shared  buff/cache   available
Mem:           62Gi       267Mi        62Gi       1.0Mi       290Mi        61Gi
Swap:          31Gi          0B        31Gi

Signed-off-by: Neil Sun <neilsun@xxxxxxxxxx>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 562e87cb..81d770a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -702,7 +702,7 @@ void drop_slab_node(int nid)
 			return;
 
 		freed = 0;
-		memcg = mem_cgroup_iter(NULL, NULL, NULL);
+		memcg = mem_cgroup_from_task(current);
 		do {
 			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
 		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
-- 
2.7.4