@@ -1289,6 +1289,20 @@ PAGE_SIZE multiple when read back.
Shows pressure stall information for memory. See
Documentation/accounting/psi.txt for details.
+ memory.force_empty
+ This interface is provided to make cgroup's memory usage empty.
+ When writing anything to this
+
+ # echo 0 > memory.force_empty
+
+ the cgroup will be reclaimed and as many pages reclaimed as possible.
+
+ The typical use case for this interface is before calling rmdir().
+ Though rmdir() offlines memcg, but the memcg may still stay there due to
+ charged file caches. Some out-of-use page caches may keep charged until
+ memory pressure happens. If you want to avoid that, force_empty will be
+ useful.
+
Usage Guidelines
~~~~~~~~~~~~~~~~
@@ -5743,6 +5743,10 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
.seq_show = wipe_on_offline_show,
.write_u64 = wipe_on_offline_write,
},
+ {
+ .name = "force_empty",
+ .write = mem_cgroup_force_empty_write,
+ },
{ } /* terminate */
};
The default hierarchy doesn't support force_empty, but there are some usecases which create and remove memcgs very frequently, and the tasks in the memcg may just access the files which are unlikely accessed by anyone else. So, we prefer force_empty the memcg before rmdir'ing it to reclaim the page cache so that they don't get accumulated to incur unnecessary memory pressure. Since the memory pressure may incur direct reclaim to harm some latency sensitive applications. There is another patch which introduces asynchronous memory reclaim when offlining, but the behavior of force_empty is still needed by some usecases which want to get the memory reclaimed immediately. So, bring force_empty interface in default hierarchy too. Cc: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> --- Documentation/admin-guide/cgroup-v2.rst | 14 ++++++++++++++ mm/memcontrol.c | 4 ++++ 2 files changed, 18 insertions(+)