Re: [PATCH v2 1/4] mm/highmem: Fix kernel-doc warnings in highmem*.h

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Ira Weiny <ira.weiny@intel.com>
Cc: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
	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>,
	linux-kernel@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
	linux-doc@vger.kernel.org, outreachy@lists.linux.dev,
	"Acked-by : Mike Rapoport" <rppt@linux.ibm.com>
Subject: Re: [PATCH v2 1/4] mm/highmem: Fix kernel-doc warnings in highmem*.h
Date: Wed, 25 May 2022 11:34:16 +0200	[thread overview]
Message-ID: <Yo34GGK62yVkPzZy@linutronix.de> (raw)
In-Reply-To: <YmwLXvtSgl2BA2mC@iweiny-desk3>

On 2022-04-29 08:59:26 [-0700], Ira Weiny wrote:
> I think some discussion needs to happen around this API.
> 
> Highmem has little use.  I don't think anyone disagrees with Linus there.
> (Although I think there are still a few users out there.)

arm32 is still built and they have sometimes 1 - 2 GiB of memory.

> kmap may be a poor name for an API without the highmem functionality.  But
> perhaps not.  One could interpret it to mean simply getting the kernel mapping
> of the page rather than creating one.  After all that is what 64bit has done
> all along.
> 
> This interpretation helps when you consider features which attempt to layer the
> direct map with additional protections like PKS.[1]  Those protections mean
> that a simple page_address() is insufficient to access the direct map.
> 
> As far as calling kmap() and kmap_atomic() deprecated I'm ok with that if the
> community is.
> 
> The current kmap() call sites need work and Fabio's work on auditing them is
> extremely helpful.  That said, if we officially deprecate kmap_atomic() then
> those sites could be added to the list for rework.

Maybe I oversee something obvious but there is no problem with removing
kmap_atomic*() and keeping only kmap_local*() around, is there?
I never intended to deprecated kmap(), only kmap_atomic*() in favour of
kmap_local*().

> Ira

Sebastian