Re: [PATCH v3 0/5] bitmap: Introduce alloc/free helpers

[Andy Shevchenko]

On Wed, 2018-06-20 at 10:33 +0300, Yury Norov wrote:
> On Mon, Jun 18, 2018 at 04:09:58PM +0300, Andy Shevchenko wrote:
> > External Email
> > 
> > A lot of code is using allocation of bitmaps using BITS_PER_LONG()
> > macro and
> > sizeof(unsigned long) operator. The readability suffers because of
> > this.
> > 
> > The series introduces three helpers, i.e. bitmap_alloc(),
> > bitmap_zalloc() and
> > bitmap_free(), to make it more cleaner.
> 

> tools/include/linux/bitmap.h already has bitmap_alloc(),

TBH, I don't give a crap about tools. They invented something that might
or might not follow kernel APIs. At the end, it's a user space.

> and it corresponds to bitmap_zalloc() in this patch. It may 
> cause problems in future if people will copy functions that
> use bitmap_alloc between kernel code and tools. So I think
> we have to propagate this API to tools and update existing
> users of bitmap_alloc() in tools.

Propose a patch then. Perhaps I need to inform tools people about new
API coming, but that's all what I can do. Existing something in tools/
does not and should not prevent extending / changing kernel internal
APIs.

> What about code that calls specific alloc functions, like
> memblock_virt_alloc() and pcpu_mem_zalloc() in mm/percpu.c,

What about it? It's not in scope of this API for sure. The above
mentioned functions have a very limited area of usage.
Your example also a bit complicated, since it's not allocating _just_ a
bitmap, but a structure _with_ embedded bitmap.

> or devm_kcalloc() in drivers/dma/edma.c?

There is no such file in the tree. You perhaps referred to
drivers/dma/ti/edma.c.

Yes, this is a candidate to convert later on if anyone wants to do it
(with introducing devm_bitmap_alloc() / devm_bitmap_zalloc() helpers).

>  If we are going to
> unify bitmap allocations in kernel, we should think about
> unification of that cases too. Should it be additional
> flag or optional pointer to the exact allocator in
> bitmap_{,z}alloc()?

So, I prefer one step at a time. Especially taking into consideration
the problems I have to solve now with those simplest helpers I proposed.

> 
> Yury
>  
> > Patch 1 is a preparatory to avoid namespace collisions between
> > bitmap API and
> > MD bitmap. No functional changes intended.
> > 
> > Patch 2 is just orphaned from previous release cycle.
> > 
> > Patch 3 introduces new helpers.
> > 
> > Patches 4 and 5 is just an example how to use new helpers. Locally I
> > have like
> > dozen of them against different subsystems and drivers.
> > 
> > Ideally it would go through Input subsystem, thus, needs an Ack from
> > MD maintainer(s).
> > 
> > Since v2:
> > - fix compilation issue in MD bitmap code
> > - elaborate changes in commit message of patch 5
> > 
> > Since v1:
> > - added namespace fix patch against MD bitmap API
> > - moved functions to lib/bitmap.c to avoid circular dependencies
> > - appended Dmitry's tags
> > 
> > Andy Shevchenko (5):
> >   md: Avoid namespace collision with bitmap API
> >   bitmap: Drop unnecessary 0 check for u32 array operations
> >   bitmap: Add bitmap_alloc(), bitmap_zalloc() and bitmap_free()
> >   Input: gpio-keys - Switch to bitmap_zalloc()
> >   Input: evdev - Switch to bitmap API
> > 
> >  drivers/input/evdev.c                         |  16 +-
> >  drivers/input/keyboard/gpio_keys.c            |   8 +-
> >  drivers/md/dm-raid.c                          |   6 +-
> >  drivers/md/md-bitmap.c                        | 301 +++++++++----
> > -----
> >  drivers/md/md-bitmap.h                        |  46 +--
> >  drivers/md/md-cluster.c                       |  16 +-
> >  drivers/md/md.c                               |  44 +--
> >  .../md/persistent-data/dm-space-map-common.c  |  12 +-
> >  drivers/md/raid1.c                            |  20 +-
> >  drivers/md/raid10.c                           |  26 +-
> >  drivers/md/raid5-cache.c                      |   2 +-
> >  drivers/md/raid5.c                            |  24 +-
> >  include/linux/bitmap.h                        |   8 +
> >  lib/bitmap.c                                  |  28 +-
> >  14 files changed, 283 insertions(+), 274 deletions(-)
> > 
> > --
> > 2.17.1

-- 
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy