From: yangge <yangge1116@xxxxxxx>
For different CMAs, concurrent allocation of CMA memory ideally should not
require synchronization using locks. Currently, a global cma_mutex lock is
employed to synchronize all CMA allocations, which can impact the
performance of concurrent allocations across different CMAs.
To test the performance impact, follow these steps:
1. Boot the kernel with the command line argument hugetlb_cma=30G to
allocate a 30GB CMA area specifically for huge page allocations. (note:
on my machine, which has 3 nodes, each node is initialized with 10G of
CMA)
2. Use the dd command with parameters if=/dev/zero of=/dev/shm/file bs=1G
count=30 to fully utilize the CMA area by writing zeroes to a file in
/dev/shm.
3. Open three terminals and execute the following commands simultaneously:
(Note: Each of these commands attempts to allocate 10GB [2621440 * 4KB
pages] of CMA memory.)
On Terminal 1: time echo 2621440 > /sys/kernel/debug/cma/hugetlb1/alloc
On Terminal 2: time echo 2621440 > /sys/kernel/debug/cma/hugetlb2/alloc
On Terminal 3: time echo 2621440 > /sys/kernel/debug/cma/hugetlb3/alloc
We attempt to allocate pages through the CMA debug interface and use the
time command to measure the duration of each allocation.
Performance comparison:
Without this patch With this patch
Terminal1 ~7s ~7s
Terminal2 ~14s ~8s
Terminal3 ~21s ~7s
To slove problem above, we could use per-CMA locks to improve concurrent
allocation performance. This would allow each CMA to be managed
independently, reducing the need for a global lock and thus improving
scalability and performance.
Signed-off-by: yangge <yangge1116@xxxxxxx>
---
V2:
- update code and message suggested by Barry.
mm/cma.c | 7 ++++---
mm/cma.h | 1 +
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/cma.c b/mm/cma.c
index 34a4df2..a0d4d2f 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -34,7 +34,6 @@
struct cma cma_areas[MAX_CMA_AREAS];
unsigned int cma_area_count;
-static DEFINE_MUTEX(cma_mutex);
static int __init __cma_declare_contiguous_nid(phys_addr_t base,
phys_addr_t size, phys_addr_t limit,
@@ -175,6 +174,8 @@ static void __init cma_activate_area(struct cma *cma)
spin_lock_init(&cma->lock);
+ mutex_init(&cma->alloc_mutex);
+
#ifdef CONFIG_CMA_DEBUGFS
INIT_HLIST_HEAD(&cma->mem_head);
spin_lock_init(&cma->mem_head_lock);
@@ -813,9 +814,9 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
spin_unlock_irq(&cma->lock);
pfn = cmr->base_pfn + (bitmap_no << cma->order_per_bit);
- mutex_lock(&cma_mutex);
+ mutex_lock(&cma->alloc_mutex);
ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA, gfp);
- mutex_unlock(&cma_mutex);
+ mutex_unlock(&cma->alloc_mutex);
if (ret == 0) {
page = pfn_to_page(pfn);
break;
diff --git a/mm/cma.h b/mm/cma.h
index df7fc62..41a3ab0 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -39,6 +39,7 @@ struct cma {
unsigned long available_count;
unsigned int order_per_bit; /* Order of pages represented by one bit */
spinlock_t lock;
+ struct mutex alloc_mutex;
#ifdef CONFIG_CMA_DEBUGFS
struct hlist_head mem_head;
spinlock_t mem_head_lock;
--
2.7.4
