On Thu, 6 Feb 2014 14:58:21 -0800 (PST) David Rientjes <rientjes@xxxxxxxxxx> wrote:
> > > +#define MAX_REMOTE_READAHEAD 4096UL
> > > /*
> > > * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
> > > * sensible upper limit.
> > > */
> > > unsigned long max_sane_readahead(unsigned long nr)
> > > {
> > > - return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE)
> > > - + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
> > > + unsigned long local_free_page;
> > > + int nid;
> > > +
> > > + nid = numa_node_id();
>
> If you're intending this to be cached for your calls into
> node_page_state() you need nid = ACCESS_ONCE(numa_node_id()).
ugh. That's too subtle and we didn't even document it.
We could put the ACCESS_ONCE inside numa_node_id() I assume but we
still have the same problem as smp_processor_id(): the numa_node_id()
return value is wrong as soon as you obtain it if running preemptibly.
We could plaster Big Fat Warnings all over the place or we could treat
numa_node_id() and derivatives in the same way as smp_processor_id()
(which is a huge pain). Or something else, but we've left a big hand
grenade here and Raghavendra won't be the last one to pull the pin?
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