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xen-devel
Re: [Xen-devel] [PATCH] tools: fix build after recent xenpaging changes
On Fri, Jun 24, Ian Campbell wrote:
> On Fri, 2011-06-24 at 15:35 +0100, Olaf Hering wrote:
> > On Fri, Jun 24, Ian Campbell wrote:
> >
> > > > The break exits the for() loop, not the while(1). In the next iteration
> > > > page 1 may still be in paging->bitmap and tried again.
> > >
> > > I'd missed the interrupted -> 1 in the while loop. I presume there is
> > > some other exit condition which triggers once everything has been paged
> > > back in and actually causes the daemon to exit?
> >
> > If the for() loop found nothing, then this triggers:
> >
> > 775 /* If no more pages to process, exit loop */
> > 776 if ( i == paging->domain_info->max_pages )
> > 777 break;
>
> Oh yes.
>
> It's a bit counter intuitive to have a for loop which only processes the
> first thing it finds and then relying on going round another outer loop
> to pickup the second etc. It's at least O(N^2), isn't it?
>
> Why not
> count = 0;
> for ( i = 0; i < paging->domain_info->max_pages; i++ )
> {
> if ( test_bit(i, paging->bitmap) )
> {
> page_in_trigger(i);
> count++
> }
> }
> /* If no more pages to process, exit loop */
> if ( !count )
> break;
>
> That will at least process as many pages as it can on each iteration
> through the outer loop. Although it will most likely exacerbate the
> locking issue I pointed to earlier.
I think an early version of my change had something like that, but it
did not fillup the ringbuffer for some reason.
I will look at this change again and see what can be improved.
Olaf
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