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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: Dennis Zhou <dennis@kernel.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
This commit is contained in:
Dennis Zhou 2019-02-26 10:46:48 -08:00
parent 92c14cab43
commit d33d9f3dd9
1 changed files with 27 additions and 9 deletions
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36
mm/percpu.c
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@ -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 */
chunk_md->contig_hint = 0;
/* 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,