Commit d9f3a01e authored by Dennis Zhou's avatar Dennis Zhou
Browse files

percpu: introduce helper to determine if two regions overlap 



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: default avatarDennis Zhou <dennis@kernel.org>
parent 8c43004a

mm/percpu.c

+24 −4
Original line number Diff line number Diff line
@@ -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);

}