Hello,
On Friday, August 24, 2012 1:52 PM Hiroshi Doyu wrote:
> Konrad Rzeszutek Wilk <konrad.w...@oracle.com> wrote @ Fri, 24 Aug 2012
> 13:13:23 +0200:
>
> > On Fri, Aug 24, 2012 at 11:29:02AM +0300, Hiroshi Doyu wrote:
> > > struct page **pages is necessary to align with non atomic path in
> > > __iommu_get_pages(). atomic_pool() has the intialized **pages instead
> > > of just *page.
> > >
> > > Signed-off-by: Hiroshi Doyu <hd...@nvidia.com>
> > > ---
> > > arch/arm/mm/dma-mapping.c | 17 +++++++++++++----
> > > 1 files changed, 13 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> > > index 601da7a..b14ee64 100644
> > > --- a/arch/arm/mm/dma-mapping.c
> > > +++ b/arch/arm/mm/dma-mapping.c
> > > @@ -296,7 +296,7 @@ struct dma_pool {
> > > unsigned long *bitmap;
> > > unsigned long nr_pages;
> > > void *vaddr;
> > > - struct page *page;
> > > + struct page **pages;
> > > };
> > >
> > > static struct dma_pool atomic_pool = {
> > > @@ -335,12 +335,16 @@ static int __init atomic_pool_init(void)
> > > unsigned long nr_pages = pool->size >> PAGE_SHIFT;
> > > unsigned long *bitmap;
> > > struct page *page;
> > > + struct page **pages;
> > > void *ptr;
> > > int bitmap_size = BITS_TO_LONGS(nr_pages) * sizeof(long);
> > > + size_t size = nr_pages * sizeof(struct page *);
> > >
> > > - bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> > > + size += bitmap_size;
> > > + bitmap = kzalloc(size, GFP_KERNEL);
> > > if (!bitmap)
> > > goto no_bitmap;
> > > + pages = (void *)bitmap + bitmap_size;
> >
> > So you stuck a bitmap field in front of the array then?
> > Why not just define a structure where this is clearly defined
> > instead of doing the casting.
>
> I just wanted to allocate only once for the members "pool->bitmap" and
> "pool->pages" at once. Since the size of a whole bitmap isn't known in
> advance, I couldn't find any fixed type for this bitmap, which pointer
> can be shifted without casting. IOW, they are variable length.
IMHO it is better to avoid any non-trivial things in generic arch code. Merging
those 2 allocations doesn't save any significant bit of memory and might confuse
someone. Better just allocate them separately.
Best regards
--
Marek Szyprowski
Samsung Poland R&D Center
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