Re: [PATCH v2] mm/vmap: Add a notifier for when we run out of vmap address space

[Andrew Morton]

On Thu, 17 Mar 2016 13:41:56 +0000 Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:

> On Thu, Mar 17, 2016 at 01:34:59PM +0000, Chris Wilson wrote:
> > vmaps are temporary kernel mappings that may be of long duration.
> > Reusing a vmap on an object is preferrable for a driver as the cost of
> > setting up the vmap can otherwise dominate the operation on the object.
> > However, the vmap address space is rather limited on 32bit systems and
> > so we add a notification for vmap pressure in order for the driver to
> > release any cached vmappings.
> > 
> > The interface is styled after the oom-notifier where the callees are
> > passed a pointer to an unsigned long counter for them to indicate if they
> > have freed any space.
> > 
> > v2: Guard the blocking notifier call with gfpflags_allow_blocking()
> > 
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Roman Peniaev <r.peniaev@xxxxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >  include/linux/vmalloc.h |  4 ++++
> >  mm/vmalloc.c            | 27 +++++++++++++++++++++++++++
> >  2 files changed, 31 insertions(+)
> > 
> > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> > index d1f1d338af20..edd676b8e112 100644
> > --- a/include/linux/vmalloc.h
> > +++ b/include/linux/vmalloc.h
> > @@ -187,4 +187,8 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
> >  #define VMALLOC_TOTAL 0UL
> >  #endif
> >  
> > +struct notitifer_block;
> Omg. /o\

Hah.

Please move the forward declaration to top-of-file.  This prevents
people from later adding the same thing at line 100 - this has happened
before.

Apart from that, all looks OK to me - please merge it via the DRM tree
if that is more convenient.