On Fri, 2015-05-22 at 09:35 +0200, Thomas Gleixner wrote:
On Wed, 13 May 2015, Toshi Kani wrote:
> + * X86 PAT uses page flags arch_1 and uncached together to keep track of
> + * memory type of pages that have backing page struct. X86 PAT supports 4
> + * different memory types, _PAGE_CACHE_MODE_WT, _PAGE_CACHE_MODE_WC,
> + * _PAGE_CACHE_MODE_UC_MINUS and _PAGE_CACHE_MODE_WB where page's memory
> + * type has not been changed from its default.
This is a horrible sentence.
* X86 PAT supports 4 different memory types:
* - _PAGE_CACHE_MODE_WB
* - _PAGE_CACHE_MODE_WC
* - _PAGE_CACHE_MODE_UC_MINUS
* - _PAGE_CACHE_MODE_WT
* _PAGE_CACHE_MODE_WB is the default type.
Sounds good. I will update as suggested.
> * Note we do not support _PAGE_CACHE_MODE_UC here.
This can be removed as it is completely redundant.
Will remove this sentence.
> -#define _PGMT_DEFAULT 0
> +#define _PGMT_WB 0 /* default */
We just established two lines above that this is the default
Will remove this comment as well.
> #define _PGMT_WC (1UL << PG_arch_1)
> #define _PGMT_UC_MINUS (1UL << PG_uncached)
> -#define _PGMT_WB (1UL << PG_uncached | 1UL << PG_arch_1)
> +#define _PGMT_WT (1UL << PG_uncached | 1UL << PG_arch_1)
> #define _PGMT_MASK (1UL << PG_uncached | 1UL << PG_arch_1)
> #define _PGMT_CLEAR_MASK (~_PGMT_MASK)
> @@ -88,14 +88,14 @@ static inline enum page_cache_mode get_page_memtype(struct page
> unsigned long pg_flags = pg->flags & _PGMT_MASK;
> - if (pg_flags == _PGMT_DEFAULT)
> - return -1;
> + if (pg_flags == _PGMT_WB)
> + return _PAGE_CACHE_MODE_WB;
> else if (pg_flags == _PGMT_WC)
> return _PAGE_CACHE_MODE_WC;
> else if (pg_flags == _PGMT_UC_MINUS)
> return _PAGE_CACHE_MODE_UC_MINUS;
> - return _PAGE_CACHE_MODE_WB;
> + return _PAGE_CACHE_MODE_WT;
> static inline void set_page_memtype(struct page *pg,
> @@ -112,11 +112,12 @@ static inline void set_page_memtype(struct page *pg,
> case _PAGE_CACHE_MODE_UC_MINUS:
> memtype_flags = _PGMT_UC_MINUS;
> - case _PAGE_CACHE_MODE_WB:
> - memtype_flags = _PGMT_WB;
> + case _PAGE_CACHE_MODE_WT:
> + memtype_flags = _PGMT_WT;
> + case _PAGE_CACHE_MODE_WB:
> - memtype_flags = _PGMT_DEFAULT;
> + memtype_flags = _PGMT_WB; /* default */
What's the value of that comment?
/* default */
I was trying to preserve the original name of "_PGMT_DEFAULT" with the
comment because _PGMT_WB takes the place of _PGMT_DEFAULT with this
change. But I agree that this may be redundant. I will remove this
comment as well.
Aside of the, please do not use tail comments. They make code harder
> * For RAM pages, we use page flags to mark the pages with appropriate type.
> - * The page flags are limited to three types, WB, WC and UC-.
> - * WT and WP requests fail with -EINVAL, and UC gets redirected to UC-.
> + * The page flags are limited to four types, WB (default), WC, WT and UC-.
> + * WP request fails with -EINVAL, and UC gets redirected to UC-.
> + * A new memtype can only be set to the default memtype WB.
I have no idea what that line means.
I will change it to "Setting a new memory type is only allowed to a page
mapped with the default WB type."
> @@ -582,13 +583,6 @@ static enum page_cache_mode
> struct page *page;
> page = pfn_to_page(paddr >> PAGE_SHIFT);
> rettype = get_page_memtype(page);
And while you are at it please add the missing newline between the
variable declaration and code.