4.2.8-ckt7 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------ From: Johannes Weiner <[email protected]> commit b6e6edcfa40561e9c8abe5eecf1c96f8e5fd9c6f upstream. Setting the original memory.limit_in_bytes hardlimit is subject to a race condition when the desired value is below the current usage. The code tries a few times to first reclaim and then see if the usage has dropped to where we would like it to be, but there is no locking, and the workload is free to continue making new charges up to the old limit. Thus, attempting to shrink a workload relies on pure luck and hope that the workload happens to cooperate. To fix this in the cgroup2 memory.max knob, do it the other way round: set the limit first, then try enforcement. And if reclaim is not able to succeed, trigger OOM kills in the group. Keep going until the new limit is met, we run out of OOM victims and there's only unreclaimable memory left, or the task writing to memory.max is killed. This allows users to shrink groups reliably, and the behavior is consistent with what happens when new charges are attempted in excess of memory.max. Signed-off-by: Johannes Weiner <[email protected]> Acked-by: Michal Hocko <[email protected]> Cc: Vladimir Davydov <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> [ kamal: backport to 4.2-stable: no Documentation/cgroup-v2.txt ] Signed-off-by: Kamal Mostafa <[email protected]> --- mm/memcontrol.c | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 1021069..d5ff354 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1551,7 +1551,7 @@ static unsigned long mem_cgroup_get_limit(struct mem_cgroup *memcg) return limit; } -static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, +static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, int order) { struct mem_cgroup *iter; @@ -1624,6 +1624,7 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, } unlock: mutex_unlock(&oom_lock); + return chosen; } #if MAX_NUMNODES > 1 @@ -5459,6 +5460,8 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of)); + unsigned int nr_reclaims = MEM_CGROUP_RECLAIM_RETRIES; + bool drained = false; unsigned long max; int err; @@ -5467,9 +5470,36 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, if (err) return err; - err = mem_cgroup_resize_limit(memcg, max); - if (err) - return err; + xchg(&memcg->memory.limit, max); + + for (;;) { + unsigned long nr_pages = page_counter_read(&memcg->memory); + + if (nr_pages <= max) + break; + + if (signal_pending(current)) { + err = -EINTR; + break; + } + + if (!drained) { + drain_all_stock(memcg); + drained = true; + continue; + } + + if (nr_reclaims) { + if (!try_to_free_mem_cgroup_pages(memcg, nr_pages - max, + GFP_KERNEL, true)) + nr_reclaims--; + continue; + } + + mem_cgroup_events(memcg, MEMCG_OOM, 1); + if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0)) + break; + } memcg_wb_domain_size_changed(memcg); return nbytes; -- 2.7.4
