linux-kernel - Re: [PATCH 3/4] bitmap: Introduce bitmap

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Date:   Sun, 3 Jul 2022 18:20:53 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Yury Norov <yury.norov@...il.com>, agk@...hat.com,
        snitzer@...nel.org, dm-devel@...hat.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
        svens@...ux.ibm.com, almaz.alexandrovich@...agon-software.com,
        linux@...musvillemoes.dk, linux-s390@...r.kernel.org,
        ntfs3@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 3/4] bitmap: Introduce bitmap_size()

On Sun, Jul 03, 2022 at 08:50:19AM +0200, Christophe JAILLET wrote:
> Le 02/07/2022 à 23:09, Yury Norov a écrit :
> > On Sat, Jul 02, 2022 at 08:29:36PM +0200, Christophe JAILLET wrote:

...

> > This should be dropped, for sure, and kmalloc() at line 128 should be
> > replaced with bitmap_alloc().
> 
> This kmalloc() is for a structure and a flexible array.
> 
> You mean re-arranging the code to allocate the structure alone at first,
> then the bitmap?

It's one way, but it will increase fragmentation of memory. The other one
as it seems to me is to name a new API properly, i.e. bitmap_size_to_bytes().

In such case you won't need renames to begin with. And then would be able
to convert driver-by-driver in cases of duplicated code.

I think that's what confused Yuri and I kinda agree that bitmap_size() should
return bits, and not bytes. Also argument for pure bitmap_size() would be
bitmap itself, but we have no way to detect the length of bitmap because we
are using POD and not a specific data structure for it.

-- 
With Best Regards,
Andy Shevchenko