On Mon, Apr 29, 2024 at 11:06 PM Shakeel Butt <shakeel.butt@xxxxxxxxx> wrote: > > mem_cgroup_events_index is a translation table to get the right index of > the memcg relevant entry for the general vm_event_item. At the moment, > it is defined as integer array. However on a typical system the max > entry of vm_event_item (NR_VM_EVENT_ITEMS) is 113, so we don't need to > use int as storage type of the array. For now just use int8_t as type > and add a BUILD_BUG_ON() and will switch to short once NR_VM_EVENT_ITEMS > touches 127. > > Another benefit of this change is that the translation table fits in 2 > cachelines while previously it would require 8 cachelines (assuming 64 > bytes cachesline). > > Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx> > Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx> Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > --- > Changes since v2: > - Used S8_MAX instead of 127 > - Update commit message based on Yosry's feedback. > > mm/memcontrol.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 602ad5faad4d..c146187cda9c 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -607,11 +607,13 @@ static const unsigned int memcg_vm_event_stat[] = { > }; > > #define NR_MEMCG_EVENTS ARRAY_SIZE(memcg_vm_event_stat) > -static int mem_cgroup_events_index[NR_VM_EVENT_ITEMS] __read_mostly; > +static int8_t mem_cgroup_events_index[NR_VM_EVENT_ITEMS] __read_mostly; > > static void init_memcg_events(void) > { > - int i; > + int8_t i; > + > + BUILD_BUG_ON(NR_VM_EVENT_ITEMS >= S8_MAX); > > for (i = 0; i < NR_MEMCG_EVENTS; ++i) > mem_cgroup_events_index[memcg_vm_event_stat[i]] = i + 1; > -- > 2.43.0 >