linux-kernel - Re: [PATCH v3 RESEND 3/6] bitmap: Make bitmap

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Date: Mon, 12 Feb 2024 15:20:22 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Yury Norov
 <yury.norov@...il.com>, Rasmus Villemoes <linux@...musvillemoes.dk>,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, Andrew Lunn <andrew@...n.ch>, Mark Brown
 <broonie@...nel.org>, Christophe Leroy <christophe.leroy@...roup.eu>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 RESEND 3/6] bitmap: Make bitmap_onto() available to
 users

On Mon, 12 Feb 2024 16:01:38 +0200
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> On Mon, Feb 12, 2024 at 02:37:53PM +0100, Herve Codina wrote:
> > On Mon, 12 Feb 2024 14:27:16 +0200
> > Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:  
> > > On Mon, Feb 12, 2024 at 08:56:31AM +0100, Herve Codina wrote:  
> > > > Currently the bitmap_onto() is available only for CONFIG_NUMA=y case,
> > > > while some users may benefit out of it and being independent to NUMA
> > > > code.
> > > > 
> > > > Make it available to users by moving out of ifdeffery and exporting for
> > > > modules.    
> > > 
> > > Wondering if you are trying to have something like
> > > https://lore.kernel.org/lkml/20230926052007.3917389-1-andriy.shevchenko@linux.intel.com/  
> > 
> > Yes, it looks like.
> > Can you confirm that your bitmap_scatter() do the same operations as the
> > existing bitmap_onto() ?  
> 
> I have test cases to be 100% sure, but on the first glance, yes it does with
> the adjustment to the atomicity of the operations (which I do not understand
> why be atomic in the original bitmap_onto() implementation).
> 
> This actually gives a question if we should use your approach or mine.
> At least the help of bitmap_onto() is kinda hard to understand.

Agree, the bitmap_onto() code is simpler to understand than its help.

I introduced bitmap_off() to be the "reverse" bitmap_onto() operations
and I preferred to avoid duplicating function that do the same things.

On my side, I initially didn't use the bitmap_*() functions and did the the
bits manipulation by hand.
During the review, it was suggested to use the bitmap_*() family and I followed
this suggestion. I did tests to be sure that bitmap_onto() and bitmap_off() did
exactly the same things as my previous code did.

> 
> > If so, your bitmap_gather() will match my bitmap_off() (patch 4 in this
> > series).  
> 
> Yes.
> 

Regards,
Hervé