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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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