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percpu: introduce bitmap metadata blocks

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This patch introduces the bitmap metadata blocks and adds the skeleton
of the code that will be used to maintain these blocks.  Each chunk's
bitmap is made up of full metadata blocks. These blocks maintain basic
metadata to help prevent scanning unnecssarily to update hints. Full
scanning methods are used for the skeleton and will be replaced in the
coming patches. A number of helper functions are added as well to do
conversion of pages to blocks and manage offsets. Comments will be
updated as the final version of each function is added.

There exists a relationship between PAGE_SIZE, PCPU_BITMAP_BLOCK_SIZE,
the region size, and unit_size. Every chunk's region (including offsets)
is page aligned at the beginning to preserve alignment. The end is
aligned to LCM(PAGE_SIZE, PCPU_BITMAP_BLOCK_SIZE) to ensure that the end
can fit with the populated page map which is by page and every metadata
block is fully accounted for. The unit_size is already page aligned, but
must also be aligned with PCPU_BITMAP_BLOCK_SIZE to ensure full metadata
blocks.

Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Dennis Zhou (Facebook)
2017-07-24 19:02:12 -04:00
committed by Tejun Heo
parent 40064aeca3
commit ca460b3c96
3 changed files with 257 additions and 12 deletions
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12
include/linux/percpu.h
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@@ -25,6 +25,18 @@
#define PCPU_MIN_ALLOC_SHIFT 2
#define PCPU_MIN_ALLOC_SIZE (1 << PCPU_MIN_ALLOC_SHIFT)
/*
* This determines the size of each metadata block. There are several subtle
* constraints around this constant. The reserved region must be a multiple of
* PCPU_BITMAP_BLOCK_SIZE. Additionally, PCPU_BITMAP_BLOCK_SIZE must be a
* multiple of PAGE_SIZE or PAGE_SIZE must be a multiple of
* PCPU_BITMAP_BLOCK_SIZE to align with the populated page map. The unit_size
* also has to be a multiple of PCPU_BITMAP_BLOCK_SIZE to ensure full blocks.
*/
#define PCPU_BITMAP_BLOCK_SIZE PAGE_SIZE
#define PCPU_BITMAP_BLOCK_BITS (PCPU_BITMAP_BLOCK_SIZE >> \
PCPU_MIN_ALLOC_SHIFT)
/*
* Percpu allocator can serve percpu allocations before slab is
* initialized which allows slab to depend on the percpu allocator.