On Tue, Dec 24, 2019 at 02:53:25AM -0500, Yafang Shao wrote:
> The lru walker isolation function may use this memcg to do something, e.g.
> the inode isolatation function will use the memcg to do inode protection in
> followup patch. So make memcg visible to the lru walker isolation function.
>
> Something should be emphasized in this patch is it replaces
> for_each_memcg_cache_index() with for_each_mem_cgroup() in
> list_lru_walk_node(). Because there's a gap between these two MACROs that
> for_each_mem_cgroup() depends on CONFIG_MEMCG while the other one depends
> on CONFIG_MEMCG_KMEM. But as list_lru_memcg_aware() returns false if
> CONFIG_MEMCG_KMEM is not configured, it is safe to this replacement.
>
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
....
> @@ -299,17 +299,15 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
> list_lru_walk_cb isolate, void *cb_arg,
> unsigned long *nr_to_walk)
> {
> + struct mem_cgroup *memcg;
> long isolated = 0;
> - int memcg_idx;
>
> - isolated += list_lru_walk_one(lru, nid, NULL, isolate, cb_arg,
> - nr_to_walk);
> - if (*nr_to_walk > 0 && list_lru_memcg_aware(lru)) {
> - for_each_memcg_cache_index(memcg_idx) {
> + if (list_lru_memcg_aware(lru)) {
> + for_each_mem_cgroup(memcg) {
> struct list_lru_node *nlru = &lru->node[nid];
>
> spin_lock(&nlru->lock);
> - isolated += __list_lru_walk_one(nlru, memcg_idx,
> + isolated += __list_lru_walk_one(nlru, memcg,
> isolate, cb_arg,
> nr_to_walk);
> spin_unlock(&nlru->lock);
> @@ -317,7 +315,11 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
> if (*nr_to_walk <= 0)
> break;
> }
> + } else {
> + isolated += list_lru_walk_one(lru, nid, NULL, isolate, cb_arg,
> + nr_to_walk);
> }
> +
That's a change of behaviour. The old code always runs per-node
reclaim, then if the LRU is memcg aware it also runs the memcg
aware reclaim. The new code never runs global per-node reclaim
if the list is memcg aware, so shrinkers that are initialised
with the flags SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE seem
likely to have reclaim problems with mixed memcg/global memory
pressure scenarios.
e.g. if all the memory is in the per-node lists, and the memcg needs
to reclaim memory because of a global shortage, it is now unable to
reclaim global memory.....
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
