On Tue, 2005-09-27 at 11:57 -0700, Martin J. Bligh wrote:
> > Seems like from the log messages that quite a few pages are hanging
> in the cpu's cold pcp list even with the low memory conditions. Below
> is the patch to reduce the higher bound in cold pcp list (...this got
> increased with my previous change).
>
> >
> > I think we should also drain the CPU's hot and cold pcps for the
> GFP_KERNEL page requests (in the event the higher order request is not
> able to get serviced otherwise). This will still only drains the
> current CPUs pcps in an MP environment (leaving the other CPUs with
> their lists intact). I will send this patch later today.
>
> >
> > [PATCH]: Reduce the high mark in cpu's cold pcp list.
> >
> > Signed-off-by: Rohit Seth <[email protected]>
> >
> >
> > --- linux-2.6.13.old/mm/page_alloc.c 2005-09-26 10:57:07.000000000
> -0700
> > +++ linux-2.6.13.work/mm/page_alloc.c 2005-09-26 10:47:57.000000000
> -0700
> > @@ -1749,7 +1749,7 @@
> > pcp = &p->pcp[1]; /* cold*/
> > pcp->count = 0;
> > pcp->low = 0;
> > - pcp->high = 2 * batch;
> > + pcp->high = batch / 2;
> > pcp->batch = max(1UL, batch/2);
> > INIT_LIST_HEAD(&pcp->list);
> > }
> > -
>
> I don't understand. How can you set the high watermark at half the
> batch size? Makes no sense to me.
>
The batch size for the cold pcp list is getting initialized to batch/2
in the code snip above. So, this change is setting the high water mark
for cold list to same as pcp's batch number.
> And can you give a stricter definiton of what you mean by "low memory
> conditions"? I agree we ought to empty the lists before going OOM or
> anything, but not at the slightest feather of pressure ... answer lies
> somewhere inbetween ... but where?
>
In the specific case of dump information that Mattia sent earlier, there
is only 4M of free mem available at the time the order 1 request is
failing.
In general, I think if a specific higher order ( > 0) request fails that
has GFP_KERNEL set then at least we should drain the pcps.
-rohit
-
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