| Message ID | 20240427003733.3898961-2-shakeel.butt@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | memcg: reduce memory consumption by memcg stats | expand |
On Fri, Apr 26, 2024 at 5:37 PM Shakeel Butt <shakeel.butt@linux.dev> 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. Any reason not to use uint8_t (or simply u8) and U8_MAX (instead of the hardcoded 127)? > > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> > --- > mm/memcontrol.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 602ad5faad4d..53769d06053f 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -607,11 +607,14 @@ 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; > + > + /* Switch to short once this failure occurs. */ > + BUILD_BUG_ON(NR_VM_EVENT_ITEMS >= 127 /* INT8_MAX */); > > for (i = 0; i < NR_MEMCG_EVENTS; ++i) > mem_cgroup_events_index[memcg_vm_event_stat[i]] = i + 1; > -- > 2.43.0 > >
On Fri, Apr 26, 2024 at 05:42:48PM -0700, Yosry Ahmed wrote: > On Fri, Apr 26, 2024 at 5:37 PM Shakeel Butt <shakeel.butt@linux.dev> 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. > > Any reason not to use uint8_t (or simply u8) and U8_MAX (instead of > the hardcoded 127)? > Just to keep the error check simple i.e. (index < 0). If we hit 127 then we can switch to uint8_t and S8_MAX as error. Though 127 should be replaced by S8_MAX. Somehow I was grep'ing for INT8*MAX variants. Anyways if there is more support for uint8_t, I will change otherwise I will keep as is.
On Fri, Apr 26, 2024 at 05:37:27PM -0700, Shakeel Butt 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. > > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 602ad5faad4d..53769d06053f 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -607,11 +607,14 @@ 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; + + /* Switch to short once this failure occurs. */ + BUILD_BUG_ON(NR_VM_EVENT_ITEMS >= 127 /* INT8_MAX */); for (i = 0; i < NR_MEMCG_EVENTS; ++i) mem_cgroup_events_index[memcg_vm_event_stat[i]] = i + 1;
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. Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> --- mm/memcontrol.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)