[RFC] reduce latency in __purge_vmap_area_lazy

On Tue, 18 Oct 2016 08:56:05 +0200 Christoph Hellwig wrote:

Hi all,

this is my spin at sorting out the long lock hold times in
__purge_vmap_area_lazy.  It is based on the patch from Joel sent this
week.  I don't have any good numbers for it, but it survived an
xfstests run on XFS which is a significant vmalloc user.  The
changelogs could still be improved as well, but I'd rather get it
out quickly for feedback and testing.

I just tested this series, the preempt off ftrace log doesn't complain
__purge_vmap_area_lazy any more in my test case, this latency is removed!

So feel free to add

Tested-by: Jisheng Zhang <redacted>