[PATCH v2 16/23] percpu: add first_bit to keep track of the first free in the bitmap

[Dennis Zhou]

From: "Dennis Zhou (Facebook)" <dennissz...@gmail.com>

This patch adds first_bit to keep track of the first free bit in the
bitmap. This hint helps prevent scanning of fully allocated blocks.

Signed-off-by: Dennis Zhou <dennissz...@gmail.com>
---
 mm/percpu-internal.h |  2 +-
 mm/percpu-stats.c    |  1 +
 mm/percpu.c          | 17 +++++++++++++++--
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h
index 252ae9e..e60e049 100644
--- a/mm/percpu-internal.h
+++ b/mm/percpu-internal.h
@@ -36,7 +36,7 @@ struct pcpu_chunk {
        struct pcpu_block_md    *md_blocks;     /* metadata blocks */
 
        void                    *data;          /* chunk data */
-       int                     first_free;     /* no free below this */
+       int                     first_bit;      /* no free below this */
        bool                    immutable;      /* no [de]population allowed */
        int                     start_offset;   /* the overlap with the previous
                                                   region to have a page aligned
diff --git a/mm/percpu-stats.c b/mm/percpu-stats.c
index ad03d73..6142484 100644
--- a/mm/percpu-stats.c
+++ b/mm/percpu-stats.c
@@ -121,6 +121,7 @@ static void chunk_map_stats(struct seq_file *m, struct 
pcpu_chunk *chunk,
        P("nr_alloc", chunk->nr_alloc);
        P("max_alloc_size", chunk->max_alloc_size);
        P("empty_pop_pages", chunk->nr_empty_pop_pages);
+       P("first_bit", chunk->first_bit);
        P("free_bytes", chunk->free_bytes);
        P("contig_bytes", chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
        P("sum_frag", sum_frag);
diff --git a/mm/percpu.c b/mm/percpu.c
index 6bddc02..ad70c67 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -420,7 +420,7 @@ static void pcpu_chunk_refresh_hint(struct pcpu_chunk 
*chunk)
        chunk->contig_bits = 0;
 
        bits = nr_empty_pop_pages = 0;
-       pcpu_for_each_unpop_region(chunk->alloc_map, rs, re, 0,
+       pcpu_for_each_unpop_region(chunk->alloc_map, rs, re, chunk->first_bit,
                                   pcpu_chunk_map_bits(chunk)) {
                bits = re - rs;
 
@@ -639,7 +639,8 @@ static int pcpu_find_block_fit(struct pcpu_chunk *chunk, 
int alloc_bits,
        int bit_off, bits;
        int re; /* region end */
 
-       pcpu_for_each_unpop_region(chunk->alloc_map, bit_off, re, 0,
+       pcpu_for_each_unpop_region(chunk->alloc_map, bit_off, re,
+                                  chunk->first_bit,
                                   pcpu_chunk_map_bits(chunk)) {
                bits = re - bit_off;
 
@@ -708,6 +709,13 @@ static int pcpu_alloc_area(struct pcpu_chunk *chunk, int 
alloc_bits,
 
        chunk->free_bytes -= alloc_bits * PCPU_MIN_ALLOC_SIZE;
 
+       /* update first free bit */
+       if (bit_off == chunk->first_bit)
+               chunk->first_bit = find_next_zero_bit(
+                                       chunk->alloc_map,
+                                       pcpu_chunk_map_bits(chunk),
+                                       bit_off + alloc_bits);
+
        pcpu_block_update_hint_alloc(chunk, bit_off, alloc_bits);
 
        pcpu_chunk_relocate(chunk, oslot);
@@ -743,6 +751,9 @@ static void pcpu_free_area(struct pcpu_chunk *chunk, int 
off)
        /* update metadata */
        chunk->free_bytes += bits * PCPU_MIN_ALLOC_SIZE;
 
+       /* update first free bit */
+       chunk->first_bit = min(chunk->first_bit, bit_off);
+
        pcpu_block_update_hint_free(chunk, bit_off, bits);
 
        pcpu_chunk_relocate(chunk, oslot);
@@ -834,6 +845,8 @@ static struct pcpu_chunk * __init 
pcpu_alloc_first_chunk(unsigned long tmp_addr,
                set_bit(0, chunk->bound_map);
                set_bit(offset_bits, chunk->bound_map);
 
+               chunk->first_bit = offset_bits;
+
                pcpu_block_update_hint_alloc(chunk, 0, offset_bits);
        }
 
-- 
2.9.3