Commit d33d9f3d authored by Dennis Zhou's avatar Dennis Zhou
Browse files

percpu: use chunk scan_hint to skip some scanning 



Just like blocks, chunks now maintain a scan_hint. This can be used to
skip some scanning by promoting the scan_hint to be the contig_hint.
The chunk's scan_hint is primarily updated on the backside and relies on
full scanning when a block becomes free or the free region spans across
blocks.

Signed-off-by: default avatarDennis Zhou <dennis@kernel.org>
Reviewed-by: default avatarPeng Fan <peng.fan@nxp.com>
parent 92c14cab

mm/percpu.c

+27 −9
Original line number Diff line number Diff line
@@ -707,20 +707,31 @@ static void pcpu_block_update_scan(struct pcpu_chunk *chunk, int bit_off, 
/**

 * pcpu_chunk_refresh_hint - updates metadata about a chunk

 * @chunk: chunk of interest

 * @full_scan: if we should scan from the beginning

 *

 * Iterates over the metadata blocks to find the largest contig area.

 * It also counts the populated pages and uses the delta to update the

 * global count.

 * A full scan can be avoided on the allocation path as this is triggered

 * if we broke the contig_hint.  In doing so, the scan_hint will be before

 * the contig_hint or after if the scan_hint == contig_hint.  This cannot

 * be prevented on freeing as we want to find the largest area possibly

 * spanning blocks.

 */

static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk)

static void pcpu_chunk_refresh_hint(struct pcpu_chunk *chunk, bool full_scan)

{

	struct pcpu_block_md *chunk_md = &chunk->chunk_md;

	int bit_off, bits;



	/* clear metadata */

	/* promote scan_hint to contig_hint */

	if (!full_scan && chunk_md->scan_hint) {

		bit_off = chunk_md->scan_hint_start + chunk_md->scan_hint;

		chunk_md->contig_hint_start = chunk_md->scan_hint_start;

		chunk_md->contig_hint = chunk_md->scan_hint;

		chunk_md->scan_hint = 0;

	} else {

		bit_off = chunk_md->first_free;

		chunk_md->contig_hint = 0;

	}



	bit_off = chunk_md->first_free;

	bits = 0;

	pcpu_for_each_md_free_region(chunk, bit_off, bits) {

		pcpu_block_update(chunk_md, bit_off, bit_off + bits);
@@ -880,6 +891,13 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, 
	if (nr_empty_pages)

		pcpu_update_empty_pages(chunk, -nr_empty_pages);



	if (pcpu_region_overlap(chunk_md->scan_hint_start,

				chunk_md->scan_hint_start +

				chunk_md->scan_hint,

				bit_off,

				bit_off + bits))

		chunk_md->scan_hint = 0;



	/*

	 * The only time a full chunk scan is required is if the chunk

	 * contig hint is broken.  Otherwise, it means a smaller space
@@ -890,7 +908,7 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off, 
				chunk_md->contig_hint,

				bit_off,

				bit_off + bits))

		pcpu_chunk_refresh_hint(chunk);

		pcpu_chunk_refresh_hint(chunk, false);

}



/**
@@ -1001,7 +1019,7 @@ static void pcpu_block_update_hint_free(struct pcpu_chunk *chunk, int bit_off, 
	 * the else condition below.

	 */

	if (((end - start) >= PCPU_BITMAP_BLOCK_BITS) || s_index != e_index)

		pcpu_chunk_refresh_hint(chunk);

		pcpu_chunk_refresh_hint(chunk, true);

	else

		pcpu_block_update(&chunk->chunk_md,

				  pcpu_block_off_to_off(s_index, start),
@@ -1074,7 +1092,7 @@ static int pcpu_find_block_fit(struct pcpu_chunk *chunk, int alloc_bits, 
	if (bit_off + alloc_bits > chunk_md->contig_hint)

		return -1;



	bit_off = chunk_md->first_free;

	bit_off = pcpu_next_hint(chunk_md, alloc_bits);

	bits = 0;

	pcpu_for_each_fit_region(chunk, alloc_bits, align, bit_off, bits) {

		if (!pop_only || pcpu_is_populated(chunk, bit_off, bits,

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