[Stable-review] [08/45] mm, x86: Saving vmcore with non-lazy freeing of vmas

[Greg KH]

On Sat, Nov 20, 2010 at 02:16:12AM +0000, Ben Hutchings wrote:
> On Fri, 2010-11-19 at 13:42 -0800, Greg KH wrote:
> > 2.6.32-stable review patch.  If anyone has any objections, please let us know.
> > 
> > ------------------
> > 
> > From: Cliff Wickman <cpw at sgi.com>
> > 
> > commit 3ee48b6af49cf534ca2f481ecc484b156a41451d upstream.
> > 
> > During the reading of /proc/vmcore the kernel is doing
> > ioremap()/iounmap() repeatedly. And the buildup of un-flushed
> > vm_area_struct's is causing a great deal of overhead. (rb_next()
> > is chewing up most of that time).
> > 
> > This solution is to provide function set_iounmap_nonlazy(). It
> > causes a subsequent call to iounmap() to immediately purge the
> > vma area (with try_purge_vmap_area_lazy()).
> > 
> > With this patch we have seen the time for writing a 250MB
> > compressed dump drop from 71 seconds to 44 seconds.
> [...]
> 
> Useful, but it doesn't seem to meet the criteria for stable updates.

I disagree, it's a major speedup, and an obvious bugfix for the problem.

thanks,

greg k-h