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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, dave.hansen@intel.com,
	Elliott@hp.com
Subject: Re: [PATCH v3 6/6] x86, mm: Support huge KVA mappings on x86
Date: Tue, 3 Mar 2015 14:44:14 -0800	[thread overview]
Message-ID: <20150303144414.9f97ef25ad8aed7d112896bf@linux-foundation.org> (raw)
In-Reply-To: <1425404664-19675-7-git-send-email-toshi.kani@hp.com>

On Tue,  3 Mar 2015 10:44:24 -0700 Toshi Kani <toshi.kani@hp.com> wrote:

> This patch implements huge KVA mapping interfaces on x86.
> 
> On x86, MTRRs can override PAT memory types with a 4KB granularity.
> When using a huge page, MTRRs can override the memory type of the
> huge page, which may lead a performance penalty.  The processor
> can also behave in an undefined manner if a huge page is mapped to
> a memory range that MTRRs have mapped with multiple different memory
> types.  Therefore, the mapping code falls back to use a smaller page
> size toward 4KB when a mapping range is covered by non-WB type of
> MTRRs.  The WB type of MTRRs has no affect on the PAT memory types.
> 
> pud_set_huge() and pmd_set_huge() call mtrr_type_lookup() to see
> if a given range is covered by MTRRs.  MTRR_TYPE_WRBACK indicates
> that the range is either covered by WB or not covered and the MTRR
> default value is set to WB.  0xFF indicates that MTRRs are disabled.
> 
> HAVE_ARCH_HUGE_VMAP is selected when X86_64 or X86_32 with X86_PAE
> is set.  X86_32 without X86_PAE is not supported since such config
> can unlikey be benefited from this feature, and there was an issue
> found in testing.
> 
> ...
>
> +
> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> +int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
> +{
> +	u8 mtrr;
> +
> +	/*
> +	 * Do not use a huge page when the range is covered by non-WB type
> +	 * of MTRRs.
> +	 */
> +	mtrr = mtrr_type_lookup(addr, addr + PUD_SIZE);
> +	if ((mtrr != MTRR_TYPE_WRBACK) && (mtrr != 0xFF))
> +		return 0;

It would be good to notify the operator in some way when this happens. 
Otherwise the kernel will run more slowly and there's no way of knowing
why.  I guess slap a pr_info() in there.  Or maybe pr_warn()?

> +	prot = pgprot_4k_2_large(prot);
> +
> +	set_pte((pte_t *)pud, pfn_pte(
> +		(u64)addr >> PAGE_SHIFT,
> +		__pgprot(pgprot_val(prot) | _PAGE_PSE)));
> +
> +	return 1;
> +}
> +
> +int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
> +{
> +	u8 mtrr;
> +
> +	/*
> +	 * Do not use a huge page when the range is covered by non-WB type
> +	 * of MTRRs.
> +	 */
> +	mtrr = mtrr_type_lookup(addr, addr + PMD_SIZE);
> +	if ((mtrr != MTRR_TYPE_WRBACK) && (mtrr != 0xFF))
> +		return 0;
> +
> +	prot = pgprot_4k_2_large(prot);
> +
> +	set_pte((pte_t *)pmd, pfn_pte(
> +		(u64)addr >> PAGE_SHIFT,
> +		__pgprot(pgprot_val(prot) | _PAGE_PSE)));
> +
> +	return 1;
> +}
>
> +int pud_clear_huge(pud_t *pud)
> +{
> +	if (pud_large(*pud)) {
> +		pud_clear(pud);
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +int pmd_clear_huge(pmd_t *pmd)
> +{
> +	if (pmd_large(*pmd)) {
> +		pmd_clear(pmd);
> +		return 1;
> +	}
> +
> +	return 0;
> +}

I didn't see anywhere where the return values of these functions are
documented.  It's all fairly obvious, but we could help the rearers
a bit.



  reply	other threads:[~2015-03-03 22:44 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-03 17:44 [PATCH v3 0/6] Kernel huge I/O mapping support Toshi Kani
2015-03-03 17:44 ` [PATCH v3 1/6] mm: Change __get_vm_area_node() to use fls_long() Toshi Kani
2015-03-03 17:44 ` [PATCH v3 2/6] lib: Add huge I/O map capability interfaces Toshi Kani
2015-03-03 17:44 ` [PATCH v3 3/6] mm: Change ioremap to set up huge I/O mappings Toshi Kani
2015-03-04 22:09   ` Ingo Molnar
2015-03-04 23:15     ` Toshi Kani
2015-03-03 17:44 ` [PATCH v3 4/6] mm: Change vunmap to tear down huge KVA mappings Toshi Kani
2015-03-03 17:44 ` [PATCH v3 5/6] x86, mm: Support huge I/O mapping capability I/F Toshi Kani
2015-03-03 17:44 ` [PATCH v3 6/6] x86, mm: Support huge KVA mappings on x86 Toshi Kani
2015-03-03 22:44   ` Andrew Morton [this message]
2015-03-03 23:14     ` Toshi Kani
2015-03-04  1:00       ` Andrew Morton
2015-03-04 16:23         ` Toshi Kani
2015-03-04 20:17           ` Ingo Molnar
2015-03-04 21:16             ` Toshi Kani

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