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Date: Wed, 20 Dec 2017 11:06:50 +0100 From: Michal Hocko <mhocko@...nel.org> To: kemi <kemi.wang@...el.com> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...hsingularity.net>, Johannes Weiner <hannes@...xchg.org>, Christopher Lameter <cl@...ux.com>, YASUAKI ISHIMATSU <yasu.isimatu@...il.com>, Andrey Ryabinin <aryabinin@...tuozzo.com>, Nikolay Borisov <nborisov@...e.com>, Pavel Tatashin <pasha.tatashin@...cle.com>, David Rientjes <rientjes@...gle.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Dave <dave.hansen@...ux.intel.com>, Andi Kleen <andi.kleen@...el.com>, Tim Chen <tim.c.chen@...el.com>, Jesper Dangaard Brouer <brouer@...hat.com>, Ying Huang <ying.huang@...el.com>, Aaron Lu <aaron.lu@...el.com>, Aubrey Li <aubrey.li@...el.com>, Linux MM <linux-mm@...ck.org>, Linux Kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 4/5] mm: use node_page_state_snapshot to avoid deviation 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@suse.cz > > 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@...el.com> > >> --- > >> 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
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