On 2017年12月20日 18:06, Michal Hocko wrote: > 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. > That is because we have much larger threshold size for NUMA counters, that means larger deviation. So, the number in local cpus may not be simply ignored. >>>> 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 >>>> >>> > -- 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>
