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SubjectRe: USBFS Memory allocation Bug
On Sun, Mar 14, 2010 at 07:31:14PM -0400, Andrew Morton wrote:
> On Thu, 11 Mar 2010 11:56:22 -0500 (EST) Alan Stern <stern@rowland.harvard.edu> wrote:
>
> > On Wed, 10 Mar 2010, Mel Gorman wrote:
> >
> > > > > Is there any means for the driver to take the large request, break it up
> > > > > into multiple smaller requests and submit them one at a time?
> > > >
> > > > In theory almost anything is possible. But it would be a big effort
> > > > and not consistent with the way the rest of the driver works.
> > > >
> > >
> > > Then about the only other suggestion would be a mempool containing a small
> > > number of largest-possible buffers that is enabled if there is no swap
> > > available.
> >
> > Considering that this is the first report I have heard about this sort
> > of problem, and that adding swap space would probably fix it, I'm not
> > inclined to make any changes.
>
> Adding swap space is unlikely to help here. For an order-6 allocation
> the page allocator will go into wtf-youre-kidding-me mode and won't
> even bother trying.
>

It will try and make the allocation and probably enter direct reclaim
and do a lumpy reclaim for contiguous blocks. What it won't do is retry
as many times as an allocation order <= PAGE_ALLOC_COSTLY_ORDER.

> Asking the allocator for 2^6 physically contiguous pages is terribly
> unreliable and shouldn't be done by any kernel code which wants to be
> useful.
>

This remains true. With swap, the high-order allocation attempt might succeed
many of the times but there will still be situations where it fails.

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab


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