On Tue, May 18, 2010 at 12:09:31AM +0800, Christoph Lameter wrote:
> On Mon, 17 May 2010, Haicheng Li wrote:
>
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 72c1211..0729a82 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2783,6 +2783,20 @@ static __init_refok int __build_all_zonelists(void
> > *data)
> > {
> > int nid;
> > int cpu;
> > +#ifdef CONFIG_MEMORY_HOTPLUG
> > + struct zone_online_info *new = (struct zone_online_info *)data;
> > +
> > + /*
> > + * Populate the new zone before build zonelists, which could
> > + * happen only when onlining a new node after system is booted.
> > + */
> > + if (new) {
> > + /* We are expecting a new memory block here. */
> > + WARN_ON(!new->onlined_pages);
> > + new->zone->present_pages += new->onlined_pages;
> > + new->zone->zone_pgdat->node_present_pages +=
> > new->onlined_pages;
> > + }
> > +#endif
>
>
> Building a zonelist now has the potential side effect of changes to the
> size of the zone?
Yeah, this sounds a bit hacky.
> Can we have a global mutex that protects against size modification of
> zonelists instead? And it could also serialize the pageset setup?
Good suggestion. We could make zone_pageset_mutex a global mutex and
take it in all the functions that call build_all_zonelists() --
currently only online_pages() and numa_zonelist_order_handler().
This can equally fix the possible race:
CPU0 CPU1 CPU2
(1) zone->present_pages += online_pages;
(2) build_all_zonelists();
(3) alloc_page();
(4) free_page();
(5) build_all_zonelists();
(6) __build_all_zonelists();
(7) zone->pageset = alloc_percpu();
In step (3,4), zone->pageset still points to boot_pageset, so bad
things may happen if 2+ nodes are in this state. Even if only 1 node
is accessing the boot_pageset, (3) may still consume too much memory
to fail the memory allocations in step (7).
Thanks,
Fengguang
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