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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Ira Weiny <ira.weiny@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Will Deacon <will@kernel.org>,
        Peter Collingbourne <pcc@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        linux-kernel@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        linux-doc@vger.kernel.org, outreachy@lists.linux.dev,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 3/4] Documentation/vm: Remove "Using kmap-atomic" from highmem.rst.
Date:   Fri, 22 Apr 2022 22:09:03 +0200
Message-ID: <2370538.jE0xQCEvom@leap>
In-Reply-To: <YmL2EQhfQLMoU1WV@iweiny-desk3>
References: <20220421180200.16901-1-fmdefrancesco@gmail.com> <20220421180200.16901-4-fmdefrancesco@gmail.com> <YmL2EQhfQLMoU1WV@iweiny-desk3>
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On venerd=C3=AC 22 aprile 2022 20:38:09 CEST Ira Weiny wrote:
> On Thu, Apr 21, 2022 at 08:01:59PM +0200, Fabio M. De Francesco wrote:
> > The use of kmap_atomic() is deprecated in favor of kmap_local_page().
>=20
> I'm not sure deprecated is the right word.

OK, in v2 I won't use "deprecated". Instead I'll say something about a=20
strong preference to avoid its use. The reason why developers should avoid=
=20
kmap_atomic() are explained in 4/4 (I've copy-pasted some lines here for=20
your convenience):

+  Each call of kmap_atomic() in the kernel creates a non-preemptible=20
section
+  and disable pagefaults. This could be a source of unwanted latency, so=20
it
+  should be only used if it is absolutely required, otherwise=20
kmap_local_page()
+  should be used where it is feasible.

> And I think the fact that this
> documentation is stale is a better reason for the patch as is.
>=20
> This series should end up indicating the desire to stop growing kmap()=20
and
> kmap_atomic() call sites and that their deprecation is on the horizon. =20
I've
> not read the text in patch 4/4 yet.

I'll wait for your review of 4/4 before sending v2.

>=20
> > For
> > this reason the "Using kmap_atomic" section in highmem.rst is obsolete=
=20
and
> > unnecessary.
>=20
> A lot of the text is obsolete (and redundant) but the example code might=
=20
be
> useful.
>=20
> Why not move the example and relevant bits into the kdoc for=20
kmap_atomic()
> which is then automatically picked up via patch 2/4.

Yes, I agree with you. I'll take into account your suggestion for v2.

However, as I said above, I'll hold v2 until you have time to review 4/4=20
for the purpose to not miss any changes that you might require for that=20
patch too.

=46urthermore, while working on v2, I think that I'll extend this series wi=
th=20
one or two patch more, in order to address other issues I noticed.=20

Thanks,

=46abio=20