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From: Andrew Morton <akpm@linux-foundation.org>
To: Toshi Kani <toshi.kani@hp.com>
Cc: hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com,
	arnd@arndb.de, linux-mm@kvack.org, x86@kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 2/7] lib: Add huge I/O map capability interfaces
Date: Mon, 26 Jan 2015 15:54:56 -0800	[thread overview]
Message-ID: <20150126155456.a40df49e42b1b7f8077421f4@linux-foundation.org> (raw)
In-Reply-To: <1422314009-31667-3-git-send-email-toshi.kani@hp.com>

On Mon, 26 Jan 2015 16:13:24 -0700 Toshi Kani <toshi.kani@hp.com> wrote:

> Add ioremap_pud_enabled() and ioremap_pmd_enabled(), which
> return 1 when I/O mappings of pud/pmd are enabled on the kernel.
> 
> ioremap_huge_init() calls arch_ioremap_pud_supported() and
> arch_ioremap_pmd_supported() to initialize the capabilities.
> 
> A new kernel option "nohgiomap" is also added, so that user can
> disable the huge I/O map capabilities if necessary.

Why?  What's the problem with leaving it enabled?

> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2304,6 +2304,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			register save and restore. The kernel will only save
>  			legacy floating-point registers on task switch.
>  
> +	nohgiomap	[KNL,x86] Disable huge I/O mappings.

That reads like "no high iomap" to me.  "nohugeiomap" would be better.

> --- a/lib/ioremap.c
> +++ b/lib/ioremap.c
> @@ -13,6 +13,44 @@
>  #include <asm/cacheflush.h>
>  #include <asm/pgtable.h>
>  
> +#ifdef CONFIG_HUGE_IOMAP
> +int __read_mostly ioremap_pud_capable;
> +int __read_mostly ioremap_pmd_capable;
> +int __read_mostly ioremap_huge_disabled;
> +
> +static int __init set_nohgiomap(char *str)
> +{
> +	ioremap_huge_disabled = 1;
> +	return 0;
> +}
> +early_param("nohgiomap", set_nohgiomap);

Why early?

> +static inline void ioremap_huge_init(void)
> +{
> +	if (!ioremap_huge_disabled) {
> +		if (arch_ioremap_pud_supported())
> +			ioremap_pud_capable = 1;
> +		if (arch_ioremap_pmd_supported())
> +			ioremap_pmd_capable = 1;
> +	}
> +}
> +
> +static inline int ioremap_pud_enabled(void)
> +{
> +	return ioremap_pud_capable;
> +}
> +
> +static inline int ioremap_pmd_enabled(void)
> +{
> +	return ioremap_pmd_capable;
> +}
> +
> +#else	/* !CONFIG_HUGE_IOMAP */
> +static inline void ioremap_huge_init(void) { }
> +static inline int ioremap_pud_enabled(void) { return 0; }
> +static inline int ioremap_pmd_enabled(void) { return 0; }
> +#endif	/* CONFIG_HUGE_IOMAP */
> +
>  static int ioremap_pte_range(pmd_t *pmd, unsigned long addr,
>  		unsigned long end, phys_addr_t phys_addr, pgprot_t prot)
>  {
> @@ -74,6 +112,12 @@ int ioremap_page_range(unsigned long addr,
>  	unsigned long start;
>  	unsigned long next;
>  	int err;
> +	static int ioremap_huge_init_done;
> +
> +	if (!ioremap_huge_init_done) {
> +		ioremap_huge_init_done = 1;
> +		ioremap_huge_init();
> +	}

Looks hacky.  Why can't we just get the startup ordering correct?  It
at least needs a comment which fully explains the situation.


  reply	other threads:[~2015-01-26 23:55 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-26 23:13 [RFC PATCH 0/7] Kernel huge I/O mapping support Toshi Kani
2015-01-26 23:13 ` [RFC PATCH 1/7] mm: Change __get_vm_area_node() to use fls_long() Toshi Kani
2015-01-26 23:13 ` [RFC PATCH 2/7] lib: Add huge I/O map capability interfaces Toshi Kani
2015-01-26 23:54   ` Andrew Morton [this message]
2015-01-27  1:01     ` Toshi Kani
2015-01-27 21:37       ` Andrew Morton
2015-01-27 22:01         ` Toshi Kani
2015-02-05 20:56       ` Toshi Kani
2015-01-26 23:13 ` [RFC PATCH 3/7] mm: Change ioremap to set up huge I/O mappings Toshi Kani
2015-01-26 23:58   ` Andrew Morton
2015-01-27  0:01     ` Toshi Kani
2015-01-26 23:13 ` [RFC PATCH 4/7] mm: Change vunmap to tear down huge KVA mappings Toshi Kani
2015-01-26 23:13 ` [RFC PATCH 5/7] x86, mm: Support huge KVA mappings on x86 Toshi Kani
2015-01-26 23:13 ` [RFC PATCH 6/7] x86, mm: Support huge I/O " Toshi Kani
2015-01-26 23:13 ` [RFC PATCH 7/7] mm: Add config HUGE_IOMAP to enable huge I/O mappings Toshi Kani

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