KUROSAWA Takahiro wrote:
> This patch implements the pzone (pseudo zone). A pzone can be used
> for reserving pages in a zone. Pzones are implemented by extending
> the zone structure and act almost the same as the conventional zones;
> we can specify pzones in a zonelist for __alloc_pages() and the vmscan
> code works on pzones with few modifications.
>
> Signed-off-by: KUROSAWA Takahiro <[EMAIL PROTECTED]>
[...]
> -/* Page flags: | [SECTION] | [NODE] | ZONE | ... | FLAGS | */
> -#define SECTIONS_PGOFF ((sizeof(unsigned long)*8) -
> SECTIONS_WIDTH)
> +/* Page flags: | [PZONE] | [SECTION] | [NODE] | ZONE | ... | FLAGS | */
> +#define PZONE_BIT_PGOFF ((sizeof(unsigned long)*8) -
> PZONE_BIT_WIDTH)
> +#define SECTIONS_PGOFF (PZONE_BIT_PGOFF - SECTIONS_WIDTH)
> #define NODES_PGOFF (SECTIONS_PGOFF - NODES_WIDTH)
> #define ZONES_PGOFF (NODES_PGOFF - ZONES_WIDTH)
In general this PZONE bit is really a part of the zone number. Much of
the order of these bits is chosen to obtain the cheapest extraction of
the most used bits, particularly the node/zone conbination or section
number on the left. I would say put the PZONE_BIT next to ZONE
probabally to the right of it? [See below for more reasons to put it
there.]
> @@ -431,6 +438,7 @@ void put_page(struct page *page);
> * sections we define the shift as 0; that plus a 0 mask ensures
> * the compiler will optimise away reference to them.
> */
> +#define PZONE_BIT_PGSHIFT (PZONE_BIT_PGOFF * (PZONE_BIT_WIDTH != 0))
> #define SECTIONS_PGSHIFT (SECTIONS_PGOFF * (SECTIONS_WIDTH != 0))
> #define NODES_PGSHIFT (NODES_PGOFF * (NODES_WIDTH != 0))
> #define ZONES_PGSHIFT (ZONES_PGOFF * (ZONES_WIDTH != 0))
> @@ -443,10 +451,11 @@ void put_page(struct page *page);
> #endif
> #define ZONETABLE_PGSHIFT ZONES_PGSHIFT
>
> -#if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED
> -#error SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED
> +#if PZONE_BIT_WIDTH+SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED
> +#error PZONE_BIT_WIDTH+SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH >
> FLAGS_RESERVED
> #endif
Do we have any bits left in the reserve on 32 bit machines? The reserve
at last look was only 8 bits and there was little if any headroom in the
rest of the flags word to extend it; if memory serves at least 22 of the
24 remaining bits was accounted for. Has this been tested on any such
machines?
> +#define PZONE_BIT_MASK ((1UL << PZONE_BIT_WIDTH) - 1)
> #define ZONES_MASK ((1UL << ZONES_WIDTH) - 1)
> #define NODES_MASK ((1UL << NODES_WIDTH) - 1)
> #define SECTIONS_MASK ((1UL << SECTIONS_WIDTH) - 1)
[...]
> +#ifdef CONFIG_PSEUDO_ZONE
> +static inline int page_in_pzone(struct page *page)
> +{
> + return (page->flags >> PZONE_BIT_PGSHIFT) & PZONE_BIT_MASK;
> +}
> +
> +static inline struct zone *page_zone(struct page *page)
> +{
> + int idx;
> +
> + idx = (page->flags >> ZONETABLE_PGSHIFT) & ZONETABLE_MASK;
> + if (page_in_pzone(page))
> + return pzone_table[idx].zone;
> + return zone_table[idx];
> +}
Could we not do this all without changing the structure of the zone
table at all by placing the PZONE_BIT either to the left or right of the
ZONE in the flags. Then ZONETABLE_MASK could be extended to cover it
when pzone's are enabled and the pzone's could be added to zone_table
instead of their own pzone_table? This would mean the code above could
be unmodified and much simpler.
> +
> +static inline unsigned long page_to_nid(struct page *page)
> +{
> + return page_zone(page)->zone_pgdat->node_id;
> +}
[...]
> +#ifdef CONFIG_PSEUDO_ZONE
> +#define MAX_NR_PZONES 1024
You seem to be allowing for 1024 pzone's here? But in
pzone_setup_page_flags() you place the pzone_idx (an offset into the
pzone_table) into the ZONE field of the page flags. This field is
typically only two bits wide? I don't see this being increased in this
patch, nor is there space for it generally to get much bigger not on 32
bit kernels anyhow (see comments about bits earlier)?
#define ZONES_SHIFT 2 /* ceil(log2(MAX_NR_ZONES)) */
Cheers.
-apw
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