Subject: Re: [PATCH v9 2/5] genalloc:support allocating specific region

From: Scott Wood <[email-masked]>
Date: Thu, 17 Sep 2015 15:25:09 -0500

On Thu, 2015-09-17 at 15:19 -0500, Scott Wood wrote:
> On Mon, 2015-09-14 at 09:38 +0800, Zhao Qiang wrote:
> > Add new algo for genalloc, it reserve a specific region of
> > memory matching the size requirement (no alignment constraint)
> > 
> > Signed-off-by: Zhao Qiang <[email-masked]>
> > ---
> > Changes for v9:
> >       - reserve a specific region, if the return region
> >       - is not during the specific region, return fail.
> > 
> >  include/linux/genalloc.h | 11 +++++++++++
> >  lib/genalloc.c           | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 41 insertions(+)
> > 
> > diff --git a/include/linux/genalloc.h b/include/linux/genalloc.h
> > index aaf3dc2..85e3b2f 100644
> > --- a/include/linux/genalloc.h
> > +++ b/include/linux/genalloc.h
> > @@ -82,6 +82,13 @@ struct genpool_data_align {
> >       int align;              /* alignment by bytes for starting address 
> > */
> >  };
> >  
> > +/*
> > + *  gen_pool data descriptor for gen_pool_fixed_fit.
> > + */
> > +struct genpool_data_fixed {
> > +     unsigned long offset;           /* The offset of the specific 
> > region */
> > +};
> > +
> >  extern struct gen_pool *gen_pool_create(int, int);
> >  extern phys_addr_t gen_pool_virt_to_phys(struct gen_pool *pool, unsigned 
> > long);
> >  extern int gen_pool_add_virt(struct gen_pool *, unsigned long, 
> > phys_addr_t,
> > @@ -121,6 +128,10 @@ extern unsigned long gen_pool_first_fit(unsigned 
> > long 
> > *map, unsigned long size,
> >               unsigned long start, unsigned int nr, void *data,
> >               struct gen_pool *pool);
> >  
> > +extern unsigned long gen_pool_fixed_fit(unsigned long *map,
> > +             unsigned long size, unsigned long start, unsigned int nr,
> > +             void *data, struct gen_pool *pool);
> > +
> 
> "fixed fit" doesn't make much sense...  How about "fixed_alloc"?
> 
>  /**
> > + * gen_pool_fixed_fit - reserve a specific region of
> > + * matching the size requirement (no alignment constraint)
> > + * @map: The address to base the search on
> > + * @size: The bitmap size in bits
> > + * @start: The bitnumber to start searching at
> > + * @nr: The number of zeroed bits we're looking for
> > + * @data: data for alignment
> > + * @pool: pool to get order from
> > + */
> > +unsigned long gen_pool_fixed_fit(unsigned long *map, unsigned long size,
> > +             unsigned long start, unsigned int nr, void *data,
> > +             struct gen_pool *pool)
> > +{
> > +     struct genpool_data_fixed *fixed_data;
> > +     int order;
> > +     unsigned long offset_bit;
> > +     unsigned long start_bit;
> > +
> > +     fixed_data = data;
> > +     order = pool->min_alloc_order;
> > +     offset_bit = fixed_data->offset >> order;
> > +     start_bit = bitmap_find_next_zero_area(map, size,
> > +                     start + offset_bit, nr, 0);
> > +     if (start_bit != offset_bit)
> > +             start_bit = size;
> > +     return start_bit;
> > +}
> > +EXPORT_SYMBOL(gen_pool_fixed_fit);
> 
> This would be simpler with bitmap_allocate_region().

Never mind, that doesn't fit with how the algorithm is used by the caller, 
and unlike genalloc isn't atomic.

-Scott