In certain cases, requestors of percpu memory may want specific
alignments. However, it is possible to end up in situations where the
contig_hint matches, but the alignment does not. This causes excess
scanning of chunks that will fail. To prevent this, if a small
allocation fails (< 32B), the chunk is moved to the empty list. Once an
allocation is freed from that chunk, it is placed back into rotation.
Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx>
---
mm/percpu.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)
diff --git a/mm/percpu.c b/mm/percpu.c
index c996bcffbb2a..3d7deece9556 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -94,6 +94,8 @@
/* the slots are sorted by free bytes left, 1-31 bytes share the same slot */
#define PCPU_SLOT_BASE_SHIFT 5
+/* chunks in slots below this are subject to being sidelined on failed alloc */
+#define PCPU_SLOT_FAIL_THRESHOLD 3
#define PCPU_EMPTY_POP_PAGES_LOW 2
#define PCPU_EMPTY_POP_PAGES_HIGH 4
@@ -488,6 +490,22 @@ static void pcpu_mem_free(void *ptr)
kvfree(ptr);
}
+static void __pcpu_chunk_move(struct pcpu_chunk *chunk, int slot,
+ bool move_front)
+{
+ if (chunk != pcpu_reserved_chunk) {
+ if (move_front)
+ list_move(&chunk->list, &pcpu_slot[slot]);
+ else
+ list_move_tail(&chunk->list, &pcpu_slot[slot]);
+ }
+}
+
+static void pcpu_chunk_move(struct pcpu_chunk *chunk, int slot)
+{
+ __pcpu_chunk_move(chunk, slot, true);
+}
+
/**
* pcpu_chunk_relocate - put chunk in the appropriate chunk slot
* @chunk: chunk of interest
@@ -505,12 +523,8 @@ static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
{
int nslot = pcpu_chunk_slot(chunk);
- if (chunk != pcpu_reserved_chunk && oslot != nslot) {
- if (oslot < nslot)
- list_move(&chunk->list, &pcpu_slot[nslot]);
- else
- list_move_tail(&chunk->list, &pcpu_slot[nslot]);
- }
+ if (oslot != nslot)
+ __pcpu_chunk_move(chunk, nslot, oslot < nslot);
}
/**
@@ -1381,7 +1395,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
bool do_warn = !(gfp & __GFP_NOWARN);
static int warn_limit = 10;
- struct pcpu_chunk *chunk;
+ struct pcpu_chunk *chunk, *next;
const char *err;
int slot, off, cpu, ret;
unsigned long flags;
@@ -1443,11 +1457,14 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
restart:
/* search through normal chunks */
for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {
- list_for_each_entry(chunk, &pcpu_slot[slot], list) {
+ list_for_each_entry_safe(chunk, next, &pcpu_slot[slot], list) {
off = pcpu_find_block_fit(chunk, bits, bit_align,
is_atomic);
- if (off < 0)
+ if (off < 0) {
+ if (slot < PCPU_SLOT_FAIL_THRESHOLD)
+ pcpu_chunk_move(chunk, 0);
continue;
+ }
off = pcpu_alloc_area(chunk, bits, bit_align, off);
if (off >= 0)
--
2.17.1
