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Subject[PATCH 09/12] percpu: use block scan_hint to only scan forward
Date
Blocks now remember the latest scan_hint. This can be used on the
allocation path as when a contig_hint is broken, we can promote the
scan_hint to the contig_hint and scan forward from there. This works
because pcpu_block_refresh_hint() is only called on the allocation path
while block free regions are updated manually in
pcpu_block_update_hint_free().

Signed-off-by: Dennis Zhou <dennis@kernel.org>
---
mm/percpu.c | 23 +++++++++++++++++------
1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index dac18968d79f..e51c151ed692 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -765,14 +765,23 @@ static void pcpu_block_refresh_hint(struct pcpu_chunk *chunk, int index)
{
struct pcpu_block_md *block = chunk->md_blocks + index;
unsigned long *alloc_map = pcpu_index_alloc_map(chunk, index);
- int rs, re; /* region start, region end */
+ int rs, re, start; /* region start, region end */
+
+ /* promote scan_hint to contig_hint */
+ if (block->scan_hint) {
+ start = block->scan_hint_start + block->scan_hint;
+ block->contig_hint_start = block->scan_hint_start;
+ block->contig_hint = block->scan_hint;
+ block->scan_hint = 0;
+ } else {
+ start = block->first_free;
+ block->contig_hint = 0;
+ }

- /* clear hints */
- block->contig_hint = block->scan_hint = 0;
- block->left_free = block->right_free = 0;
+ block->right_free = 0;

/* iterate over free areas and update the contig hints */
- pcpu_for_each_unpop_region(alloc_map, rs, re, block->first_free,
+ pcpu_for_each_unpop_region(alloc_map, rs, re, start,
PCPU_BITMAP_BLOCK_BITS) {
pcpu_block_update(block, rs, re);
}
@@ -837,6 +846,8 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off,
s_off,
s_off + bits)) {
/* block contig hint is broken - scan to fix it */
+ if (!s_off)
+ s_block->left_free = 0;
pcpu_block_refresh_hint(chunk, s_index);
} else {
/* update left and right contig manually */
@@ -870,11 +881,11 @@ static void pcpu_block_update_hint_alloc(struct pcpu_chunk *chunk, int bit_off,
if (e_off > e_block->scan_hint_start)
e_block->scan_hint = 0;

+ e_block->left_free = 0;
if (e_off > e_block->contig_hint_start) {
/* contig hint is broken - scan to fix it */
pcpu_block_refresh_hint(chunk, e_index);
} else {
- e_block->left_free = 0;
e_block->right_free =
min_t(int, e_block->right_free,
PCPU_BITMAP_BLOCK_BITS - e_off);
--
2.17.1
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