[PATCH 09/12] percpu: use block scan_hint to only scan forward

[Dennis Zhou]

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 <den...@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