| Message ID | 20250314061511.1308152-3-shakeel.butt@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | memcg: stock code cleanups | expand |
On 3/14/25 07:15, Shakeel Butt wrote: > Currently drain_obj_stock() can potentially call __refill_stock which > accesses local cpu stock and thus requires memcg stock's local_lock. > However if we look at the code paths leading to drain_obj_stock(), there > is never a good reason to refill the memcg stock at all from it. > > At the moment, drain_obj_stock can be called from reclaim, hotplug cpu > teardown, mod_objcg_state() and refill_obj_stock(). For reclaim and > hotplug there is no need to refill. For the other two paths, most > probably the newly switched objcg would be used in near future and thus > no need to refill stock with the older objcg. > > In addition, __refill_stock() from drain_obj_stock() happens on rare > cases, so performance is not really an issue. Let's just uncharge > directly instead of refill which will also decouple drain_obj_stock from > local cpu stock and local_lock requirements. > > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/memcontrol.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index c09a32e93d39..28cb75b5bc66 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2855,7 +2855,12 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) > > mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages); > memcg1_account_kmem(memcg, -nr_pages); > - __refill_stock(memcg, nr_pages); > + if (!mem_cgroup_is_root(memcg)) { > + page_counter_uncharge(&memcg->memory, nr_pages); > + if (do_memsw_account()) > + page_counter_uncharge(&memcg->memsw, > + nr_pages); > + } > > css_put(&memcg->css); > }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c09a32e93d39..28cb75b5bc66 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2855,7 +2855,12 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages); memcg1_account_kmem(memcg, -nr_pages); - __refill_stock(memcg, nr_pages); + if (!mem_cgroup_is_root(memcg)) { + page_counter_uncharge(&memcg->memory, nr_pages); + if (do_memsw_account()) + page_counter_uncharge(&memcg->memsw, + nr_pages); + } css_put(&memcg->css); }
Currently drain_obj_stock() can potentially call __refill_stock which accesses local cpu stock and thus requires memcg stock's local_lock. However if we look at the code paths leading to drain_obj_stock(), there is never a good reason to refill the memcg stock at all from it. At the moment, drain_obj_stock can be called from reclaim, hotplug cpu teardown, mod_objcg_state() and refill_obj_stock(). For reclaim and hotplug there is no need to refill. For the other two paths, most probably the newly switched objcg would be used in near future and thus no need to refill stock with the older objcg. In addition, __refill_stock() from drain_obj_stock() happens on rare cases, so performance is not really an issue. Let's just uncharge directly instead of refill which will also decouple drain_obj_stock from local cpu stock and local_lock requirements. Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> --- mm/memcontrol.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)