lkml.org 
[lkml]   [2014]   [Feb]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH V5] mm readahead: Fix readahead fail for no local memory and limit readahead pages
On Thu, 6 Feb 2014 14:58:21 -0800 (PST) David Rientjes <rientjes@google.com> 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?


\
 
 \ /
  Last update: 2014-02-07 01:01    [W:0.073 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site