Re: [PATCH 17/19] dm: get rid of superfluous gfp flags

[Mikulas Patocka]

On Fri, 15 Apr 2016, Michal Hocko wrote:

> On Fri 15-04-16 08:29:28, Mikulas Patocka wrote:
> > 
> > 
> > On Mon, 11 Apr 2016, Michal Hocko wrote:
> > 
> > > From: Michal Hocko <mhocko@xxxxxxxx>
> > > 
> > > copy_params seems to be little bit confused about which allocation flags
> > > to use. It enforces GFP_NOIO even though it uses
> > > memalloc_noio_{save,restore} which enforces GFP_NOIO at the page
> > 
> > memalloc_noio_{save,restore} is used because __vmalloc is flawed and 
> > doesn't respect GFP_NOIO properly (it doesn't use gfp flags when 
> > allocating pagetables).
> 
> Yes and there are no plans to change __vmalloc to properly propagate gfp
> flags through the whole call chain and that is why we have
> memalloc_noio thingy. If that ever changes later the GFP_NOIO can be
> added in favor of memalloc_noio API. Both are clearly redundant.
> -- 
> Michal Hocko
> SUSE Labs

You could move memalloc_noio_{save,restore} to __vmalloc. Something like

if (!(gfp_mask & __GFP_IO))
	noio_flag = memalloc_noio_save();
...
if (!(gfp_mask & __GFP_IO))
	memalloc_noio_restore(noio_flag);

That would be better than repeating this hack in every __vmalloc caller 
that need GFP_NOIO.

Mikulas