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SubjectRe: [PATCH 1/7] [v2] zram/vmalloc: Correct tunings to enable use with 64K pages
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On Fri, 2011-01-28 at 08:57 -0600, Robert Jennings wrote:
> xvmalloc will not currently function with 64K pages. Newly allocated
> pages will be inserted at an offset beyond the end of the first-level
> index. This tuning is needed to properly size the allocator for 64K
> pages.
>
> The default 3 byte shift results in a second level list size which can not
> be indexed using the 64 bits of the flbitmap in the xv_pool structure.
> The shift must increase to 4 bytes between second level list entries to
> fit the size of the first level bitmap.
>
> Here are a few statistics for structure sizes on 32- and 64-bit CPUs
> with 4KB and 64KB page sizes.
>
> bits_per_long 32 64 64
> page_size 4,096 4,096 65,535
> xv_align 4 8 8
> fl_delta 3 3 4
> num_free_lists 508 508 4,094
> xv_pool size 4,144b 8,216b 66,040b
> per object overhead 32 64 64
> zram struct 0.5GB disk 512KB 1024KB 64KB
>
> This patch maintains the current tunings for 4K pages, adds an optimal
> sizing for 64K pages and adds a safe tuning for any other page sizes.
>
> Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>

Reviewed-by: Pekka Enberg <penberg@kernel.org>



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