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.
> */
> Hmm?
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 *pg)
> > {
> > 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;
> > else
> > - 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;
> > break;
> > - case _PAGE_CACHE_MODE_WB:
> > - memtype_flags = _PGMT_WB;
> > + case _PAGE_CACHE_MODE_WT:
> > + memtype_flags = _PGMT_WT;
> > break;
> > + case _PAGE_CACHE_MODE_WB:
> > default:
> > - memtype_flags = _PGMT_DEFAULT;
> > + memtype_flags = _PGMT_WB; /* default */
>
> What's the value of that comment?
>
> default:
> /* 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
> to parse.
Got it.
> > /*
> > * 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 lookup_memtype(u64 paddr)
> > struct page *page;
> > page = pfn_to_page(paddr >> PAGE_SHIFT);
> > rettype = get_page_memtype(page);
>
> return get_page_memtype(page);
>
> And while you are at it please add the missing newline between the
> variable declaration and code.
Will do.
Thanks,
-Toshi
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