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SubjectRe: [PATCH RFC 1/3] x86: Make page cache mode a real type
On 08/22/2014 12:09 AM, Toshi Kani wrote:
> On Tue, 2014-08-19 at 15:25 +0200, jgross@suse.com wrote:
>> From: Juergen Gross <jgross@suse.com>
>>
>> At the moment there are a lot of places that handle setting or getting
>> the page cache mode by treating the pgprot bits equal to the cache mode.
>> This is only true because there are a lot of assumptions about the setup
>> of the PAT MSR. Otherwise the cache type needs to get translated into
>> pgprot bits and vice versa.
>>
>> This patch tries to prepare for that by introducing a seperate type
>> for the cache mode and adding functions to translate between those and pgprot
>> values.
>>
>> To avoid too much performance penalty the translation between cache mode
>> and pgprot values is done via tables which contain the relevant information.
>> Write-back cache mode is hard-wired to be 0, all other modes are configurable
>> via those tables. For large pages there are translation functions as the
>> PAT bit is located at different positions in the ptes of 4k and large pages.
>
> One more comment below..
>
>> diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h
> :
>> -static inline void set_page_memtype(struct page *pg, unsigned long memtype)
>> +static inline void set_page_memtype(struct page *pg,
>> + enum page_cache_mode memtype)
>> {
>> unsigned long memtype_flags = _PGMT_DEFAULT;
>> unsigned long old_flags;
>> unsigned long new_flags;
>>
>> switch (memtype) {
>> - case _PAGE_CACHE_WC:
>> + case _PAGE_CACHE_MODE_WC:
>> memtype_flags = _PGMT_WC;
>> break;
>> - case _PAGE_CACHE_UC_MINUS:
>> + case _PAGE_CACHE_MODE_UC_MINUS:
>> memtype_flags = _PGMT_UC_MINUS;
>> break;
>> - case _PAGE_CACHE_WB:
>> + case _PAGE_CACHE_MODE_WB:
>> + default:
>> memtype_flags = _PGMT_WB;
>> break;
>> }
>
> Adding the "default" case handled as _PGMT_WB is not correct here.
> free_ram_pages_type() calls set_page_memtype() with -1, which needs to
> be set to _PGMT_DEFAULT.

It says so in the comment above. I'll correct it, thanks.

Juergen



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