On Mon, Feb 10, 2025 at 2:56 PM <yangge1116@xxxxxxx> wrote:
>
> 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>
An allocation from one CMA region should not be blocked by an allocation from
another CMA region, especially since we may have multiple CMA regions or
even per-NUMA CMA regions.
Reviewed-by: Barry Song <baohua@xxxxxxxxxx>
> ---
>
> 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
>
>
Thanks
Barry
