[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 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.


thanks,

Takashi