linux-kernel - Re: [patch RFC 02/15] highmem: Provide generic variant of kmap

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Date:   Mon, 21 Sep 2020 07:28:19 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Paul McKenney <paulmck@...nel.org>, x86@...nel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Russell King <linux@...linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Vineet Gupta <vgupta@...opsys.com>,
        linux-snps-arc@...ts.infradead.org, Arnd Bergmann <arnd@...db.de>,
        Guo Ren <guoren@...nel.org>, linux-csky@...r.kernel.org,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org,
        "David S. Miller" <davem@...emloft.net>, sparclinux@...r.kernel.org
Subject: Re: [patch RFC 02/15] highmem: Provide generic variant of
 kmap_atomic*

> +# ifndef ARCH_NEEDS_KMAP_HIGH_GET
> +static inline void *arch_kmap_temporary_high_get(struct page *page)
> +{
> +	return NULL;
> +}
> +# endif

Turn this into a macro and use #ifndef on the symbol name?

> +static inline void __kunmap_atomic(void *addr)
> +{
> +	kumap_atomic_indexed(addr);
> +}
> +
> +
> +#endif /* CONFIG_KMAP_ATOMIC_GENERIC */

Stange double empty line above the endif.

> -#define kunmap_atomic(addr)                                     \
> -do {                                                            \
> -	BUILD_BUG_ON(__same_type((addr), struct page *));       \
> -	kunmap_atomic_high(addr);                                  \
> -	pagefault_enable();                                     \
> -	preempt_enable();                                       \
> -} while (0)
> -
> +#define kunmap_atomic(addr)						\
> +	do {								\
> +		BUILD_BUG_ON(__same_type((addr), struct page *));	\
> +		__kunmap_atomic(addr);					\
> +		preempt_enable();					\
> +	} while (0)

Why the strange re-indent to a form that is much less common and less
readable?

> +void *kmap_atomic_pfn_prot(unsigned long pfn, pgprot_t prot)
> +{
> +	pagefault_disable();
> +	return __kmap_atomic_pfn_prot(pfn, prot);
> +}
> +EXPORT_SYMBOL(kmap_atomic_pfn_prot);

The existing kmap_atomic_pfn & co implementation is EXPORT_SYMBOL_GPL,
and this stuff should preferably stay that way.