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percpu: introduce helper to determine if two regions overlap

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While block hints were always accurate, it's possible when spanning
across blocks that we miss updating the chunk's contig_hint. Rather than
rely on correctness of the boundaries of hints, do a full overlap
comparison.

A future patch introduces the scan_hint which makes the contig_hint
slightly fuzzy as they can at times be smaller than the actual hint.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
This commit is contained in:
Dennis Zhou 2019-02-21 15:44:35 -08:00
parent 8c43004af0
commit d9f3a01eeb
1 changed files with 24 additions and 4 deletions
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28
mm/percpu.c
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@ -546,6 +546,21 @@ static inline int pcpu_cnt_pop_pages(struct pcpu_chunk *chunk, int bit_off,
bitmap_weight(chunk->populated, page_start);
}
/*
* pcpu_region_overlap - determines if two regions overlap
* @a: start of first region, inclusive
* @b: end of first region, exclusive
* @x: start of second region, inclusive
* @y: end of second region, exclusive
*
* This is used to determine if the hint region [a, b) overlaps with the
* allocated region [x, y).
*/
static inline bool pcpu_region_overlap(int a, int b, int x, int y)
{
return (a < y) && (x < b);
}
/**
* pcpu_chunk_update - updates the chunk metadata given a free area
* @chunk: chunk of interest
@ -710,8 +725,11 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off,
PCPU_BITMAP_BLOCK_BITS,
s_off + bits);
if (s_off >= s_block->contig_hint_start &&
s_off < s_block->contig_hint_start + s_block->contig_hint) {
if (pcpu_region_overlap(s_block->contig_hint_start,
s_block->contig_hint_start +
s_block->contig_hint,
s_off,
s_off + bits)) {
/* block contig hint is broken - scan to fix it */
pcpu_block_refresh_hint(chunk, s_index);
} else {
@ -764,8 +782,10 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off,
* contig hint is broken. Otherwise, it means a smaller space
* was used and therefore the chunk contig hint is still correct.
*/
if (bit_off >= chunk->contig_bits_start &&
bit_off < chunk->contig_bits_start + chunk->contig_bits)
if (pcpu_region_overlap(chunk->contig_bits_start,
chunk->contig_bits_start + chunk->contig_bits,
bit_off,
bit_off + bits))
pcpu_chunk_refresh_hint(chunk);
}