[alsa-devel] [PATCH 1/2] ALSA: Replace snd_malloc_pages() and snd_free_pages() with standard helpers, take#2

[Takashi Iwai]

On Wed, 27 Mar 2019 15:19:51 +0100,
Michal Hocko wrote:
> 
> On Wed 27-03-19 14:51:17, Takashi Iwai wrote:
> > On Wed, 27 Mar 2019 12:47:30 +0100,
> > Michal Hocko wrote:
> > > 
> > > On Wed 27-03-19 10:29:58, Takashi Iwai wrote:
> > > > snd_malloc_pages() and snd_free_pages() are merely thin wrappers of
> > > > the standard page allocator / free functions.  Even the arguments are
> > > > compatible with some standard helpers, so there is little merit of
> > > > keeping these wrappers.
> > > > 
> > > > This patch replaces the all existing callers of snd_malloc_pages() and
> > > > snd_free_pages() with the direct calls of the standard helper
> > > > functions.  In this version, we use a recently introduced one,
> > > > alloc_pages_exact(), which suits better than the old
> > > > snd_malloc_pages() implementation for our purposes.  Then we can avoid
> > > > the waste of pages by alignment to power-of-two.
> > > > 
> > > > Since alloc_pages_exact() does split pages, we need no longer
> > > > __GFP_COMP flag; or better to say, we must not pass __GFP_COMP to
> > > > alloc_pages_exact().  So the former unconditional addition of
> > > > __GFP_COMP flag in snd_malloc_pages() is dropped, as well as in most
> > > > other places.
> > > 
> > > I haven't checked all the callers but the replacement makes sense to me.
> > > I am just wondering whether there is any hard requireemet to have all
> > > those requests to be physically contiguous or kvmalloc would suit them
> > > better.
> > 
> > Most of callers are supposed to allocate buffers that can be also
> > mmapped to user-space, so kvmalloc() won't work.  So, the explicit
> > page allocations are on purpose.
> 
> OK, I see. There is a facility to remap vmalloc pages to userspace
> (remap_vmalloc_range_partial) but I can see why you do not want to
> change the code around.

Thanks, it's good to know the remap_vmalloc_range*().
Currently we're mapping vmalloced buffer via vm fault calls.

> From the snd_malloc_pages->alloc_pages_exact point of view (I haven't
> checked all the callers) feel free to add
> Acked-by: Michal Hocko <mhocko at suse.com>

Added.


thanks,

Takashi