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

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Message-ID: <YqjAVq+1PIpVIr0p@iweiny-desk3>
Date:   Tue, 14 Jun 2022 10:07:34 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        David Sterba <dsterba@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     <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 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

> 
> Thanks for your review,
> 
> Fabio
> 
> 
>