linux-kernel - Re: [PATCH] btrfs: Replace kmap() with kmap_local

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Date:   Wed, 15 Jun 2022 07:29:55 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     David Sterba <dsterba@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Ira Weiny <ira.weiny@...el.com>, dsterba@...e.cz,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        Nick Terrell <terrelln@...com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Filipe Manana <fdmanana@...nel.org>
Subject: Re: [PATCH] btrfs: Replace kmap() with kmap_local_page() in zstd.c

On martedì 14 giugno 2022 19:07:34 CEST Ira Weiny wrote:
> On Tue, Jun 14, 2022 at 06:28:48PM +0200, Fabio M. De Francesco wrote:
> > On martedì 14 giugno 2022 16:25:21 CEST David Sterba wrote:
> > > On Tue, Jun 14, 2022 at 01:22:50AM +0200, Fabio M. De Francesco 
wrote:
> > > > On lunedì 13 giugno 2022 20:39:13 CEST David Sterba wrote:
> > > > > On Sat, Jun 11, 2022 at 03:52:03PM +0200, Fabio M. De Francesco 
> > > 
> 
> [snip]
> 
> > > > A better solution is changing the prototype of __kunmap_local(); I
> > > > suppose that Andrew won't object, but who knows?
> > > > 
> > > > (+Cc Andrew Morton).
> > > > 
> > > > I was waiting for your comments. At now I've done about 15 
conversions 
> > > > across the kernel but it's the first time I had to pass a pointer 
to 
> > const 
> > > > void to kunmap_local(). Therefore, I was not sure if changing the 
API 
> > were 
> > > > better suited (however I have already discussed this with Ira).
> > > 
> > > IMHO it should be fixed in the API.
> > > 
> > I agree with you in full.
> > 
> > At the same time when you sent this email I submitted a patch to change 
> > kunmap_local() and kunmap_atomic().
> > 
> > After Andrew takes them I'll send v2 of this patch to zstd.c without 
those 
> > unnecessary casts.
> 
> David,
> 
> Would you be willing to take this through your tree as a pre-patch to the 
kmap
> changes in btrfs?
> 
> That would be easier for Fabio and probably you and Andrew in the long 
run.
> 
> Ira

David,

Please drop the first version of the changes[1] to the API and instead take 
my second version.[2] I've only reworked the commit message (and subject, 
but this was involuntary) to make explicit that the fundamental reason 
behind these changes are semantic correctness.

Thanks,

Fabio

[1] https://lore.kernel.org/lkml/20220614142531.16478-1-fmdefrancesco@gmail.com/

[2] https://lore.kernel.org/lkml/20220615051256.31466-1-fmdefrancesco@gmail.com/