On Mon, Feb 12, 2024 at 04:36:36PM +0200, Andy Shevchenko wrote:

On Mon, Feb 12, 2024 at 03:20:22PM +0100, Herve Codina wrote:

quoted

On Mon, 12 Feb 2024 16:01:38 +0200
Andy Shevchenko [off-list ref] wrote:

...

quoted

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 also would go this way, the problems I see with the current implementation are:

Sure, opencoding and duplicating the functionality is always a bad
idea.

- being related to NUMA (and as Rasmus once pointed out better to be there);

It's 'related to NUMA' for the only reason - it's used by NUMA only.
Nothing NUMA-specific in the function itself.

Now that we've got a non-NUMA user, the bitmap_onto() is not related
to NUMA anymore.

- unclear naming, esp. proposed bitmap_off();

That's I agree. Scatter/gather from your last approach sound better.
Do you plan to send a v2?

- the quite hard to understand help text

Yes, we need a picture that would illustrate what actually happens

- atomicity when it's not needed (AFAICT).

Agree. A series of atomic ops is not atomic. For example

        if (test_bit(n, map))
                set_bit(m, map);

is not atomic as a whole. And this is what we do in bitmap_onto/off()
in a loop. This must be fixed by using underscoded version.

quoted

I did tests to be sure that bitmap_onto() and bitmap_off() did
exactly the same things as my previous code did.

Yuri, what do you think about all this?

I think your scatter/gather is better then this onto/off by naming and
implementation. If you'll send a v2, and it would work for Herve, I'd
prefer scatter/gather. But we can live with onto/off as well.

Thanks,
Yury