On Wed 22-02-17 22:31:50, hejianet wrote:
> Hi Michal
>
> On 22/02/2017 7:41 PM, Michal Hocko wrote:
> > On Wed 22-02-17 17:04:48, Jia He wrote:
> > > When I try to dynamically allocate the hugepages more than system total
> > > free memory:
> > > e.g. echo 4000 >/proc/sys/vm/nr_hugepages
> >
> > I assume that the command has terminated with less huge pages allocated
> > than requested but
> >
> Yes, at last the allocated hugepages are less than 4000
> HugePages_Total: 1864
> HugePages_Free: 1864
> HugePages_Rsvd: 0
> HugePages_Surp: 0
> Hugepagesize: 16384 kB
>
> In the bad case, although kswapd takes 100% cpu, the number of
> HugePages_Total is not increase at all.
>
> > > Node 3, zone DMA
> > [...]
> > > pages free 2951
> > > min 2821
> > > low 3526
> > > high 4231
> >
> > it left the zone below high watermark with
> >
> > > node_scanned 0
> > > spanned 245760
> > > present 245760
> > > managed 245388
> > > nr_free_pages 2951
> > > nr_zone_inactive_anon 0
> > > nr_zone_active_anon 0
> > > nr_zone_inactive_file 0
> > > nr_zone_active_file 0
> >
> > no pages reclaimable, so kswapd will not go to sleep. It would be quite
> > easy and comfortable to call it a misconfiguration but it seems that
> > it might be quite easy to hit with NUMA machines which have large
> > differences in the node sizes. I guess it makes sense to back off
> > the kswapd rather than burning CPU without any way to make forward
> > progress.
>
> agree.
please make sure that this information is in the changelog
[...]
> > > @@ -3502,6 +3503,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
> > > {
> > > pg_data_t *pgdat;
> > > int z;
> > > + int node_has_relaimable_pages = 0;
> > >
> > > if (!managed_zone(zone))
> > > return;
> > > @@ -3522,8 +3524,15 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
> > >
> > > if (zone_balanced(zone, order, classzone_idx))
> > > return;
> > > +
> > > + if (!zone_reclaimable_pages(zone))
> > > + node_has_relaimable_pages = 1;
> >
> > What, this doesn't make any sense? Did you mean if (zone_reclaimable_pages)?
>
> I mean, if any one zone has reclaimable pages, then this zone's *node* has
> reclaimable pages. Thus, the kswapN for this node should be waken up.
> e.g. node 1 has 2 zones.
> zone A has no reclaimable pages but zone B has.
> Thus node 1 has reclaimable pages, and kswapd1 will be waken up.
> I use node_has_relaimable_pages in the loop to check all the zones' reclaimable
> pages number. So I prefer the name node_has_relaimable_pages instead of
> zone_has_relaimable_pages
I still do not understand. This code starts with
node_has_relaimable_pages = 0. If you see a zone with no reclaimable
pages then you make it node_has_relaimable_pages = 1 which means that
> > > + /* Dont wake kswapd if no reclaimable pages */
> > > + if (!node_has_relaimable_pages)
> > > + return;
this will not hold and we will wake up the kswapd. I believe what
you want instead, is to skip the wake up if _all_ zones have
!zone_reclaimable_pages() Or I am missing your point. This means that
you want
if (zone_reclaimable_pages(zone)
node_has_relaimable_pages = 1;
> > > +
> > > trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
> > > wake_up_interruptible(&pgdat->kswapd_wait);
--
Michal Hocko
SUSE Labs
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