On Wed 20-12-17 14:07:35, kemi wrote: > > > On 2017年12月19日 20:43, Michal Hocko wrote: > > On Tue 19-12-17 14:39:25, Kemi Wang wrote: > >> To avoid deviation, this patch uses node_page_state_snapshot instead of > >> node_page_state for node page stats query. > >> e.g. cat /proc/zoneinfo > >> cat /sys/devices/system/node/node*/vmstat > >> cat /sys/devices/system/node/node*/numastat > >> > >> As it is a slow path and would not be read frequently, I would worry about > >> it. > > > > The changelog doesn't explain why these counters needs any special > > treatment. _snapshot variants where used only for internal handling > > where the precision really mattered. We do not have any in-tree user and > > Jack has removed this by http://lkml.kernel.org/r/20171122094416.26019-1-jack@xxxxxxx > > which is already sitting in the mmotm tree. We can re-add it but that > > would really require a _very good_ reason. > > > > Assume we have *nr* cpus, and threshold size is *t*. Thus, the maximum deviation is nr*t. > Currently, Skylake platform has hundreds of CPUs numbers and the number is still > increasing. Also, even the threshold size is kept to 125 at maximum (32765 > for NUMA counters now), the deviation is just a little too big as I have mentioned in > the log. I tend to sum the number in local cpus up when query the global stats. This is a general problem of pcp accounting. So if it needs to be addressed then do it the same way for all stats. > Also, node_page_state_snapshot is only called in slow path and I don't think that > would be a big problem. > > Anyway, it is a matter of taste. I just think it's better to have. You are making numastats special and I yet haven't heard any sounds arguments for that. But that should be discussed in the respective patch. > >> Signed-off-by: Kemi Wang <kemi.wang@xxxxxxxxx> > >> --- > >> drivers/base/node.c | 17 ++++++++++------- > >> mm/vmstat.c | 2 +- > >> 2 files changed, 11 insertions(+), 8 deletions(-) > >> > >> diff --git a/drivers/base/node.c b/drivers/base/node.c > >> index a045ea1..cf303f8 100644 > >> --- a/drivers/base/node.c > >> +++ b/drivers/base/node.c > >> @@ -169,12 +169,15 @@ static ssize_t node_read_numastat(struct device *dev, > >> "interleave_hit %lu\n" > >> "local_node %lu\n" > >> "other_node %lu\n", > >> - node_page_state(NODE_DATA(dev->id), NUMA_HIT), > >> - node_page_state(NODE_DATA(dev->id), NUMA_MISS), > >> - node_page_state(NODE_DATA(dev->id), NUMA_FOREIGN), > >> - node_page_state(NODE_DATA(dev->id), NUMA_INTERLEAVE_HIT), > >> - node_page_state(NODE_DATA(dev->id), NUMA_LOCAL), > >> - node_page_state(NODE_DATA(dev->id), NUMA_OTHER)); > >> + node_page_state_snapshot(NODE_DATA(dev->id), NUMA_HIT), > >> + node_page_state_snapshot(NODE_DATA(dev->id), NUMA_MISS), > >> + node_page_state_snapshot(NODE_DATA(dev->id), > >> + NUMA_FOREIGN), > >> + node_page_state_snapshot(NODE_DATA(dev->id), > >> + NUMA_INTERLEAVE_HIT), > >> + node_page_state_snapshot(NODE_DATA(dev->id), NUMA_LOCAL), > >> + node_page_state_snapshot(NODE_DATA(dev->id), > >> + NUMA_OTHER)); > >> } > >> > >> static DEVICE_ATTR(numastat, S_IRUGO, node_read_numastat, NULL); > >> @@ -194,7 +197,7 @@ static ssize_t node_read_vmstat(struct device *dev, > >> for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) > >> n += sprintf(buf+n, "%s %lu\n", > >> vmstat_text[i + NR_VM_ZONE_STAT_ITEMS], > >> - node_page_state(pgdat, i)); > >> + node_page_state_snapshot(pgdat, i)); > >> > >> return n; > >> } > >> diff --git a/mm/vmstat.c b/mm/vmstat.c > >> index 64e08ae..d65f28d 100644 > >> --- a/mm/vmstat.c > >> +++ b/mm/vmstat.c > >> @@ -1466,7 +1466,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat, > >> for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) { > >> seq_printf(m, "\n %-12s %lu", > >> vmstat_text[i + NR_VM_ZONE_STAT_ITEMS], > >> - node_page_state(pgdat, i)); > >> + node_page_state_snapshot(pgdat, i)); > >> } > >> } > >> seq_printf(m, > >> -- > >> 2.7.4 > >> > > -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
