Re: [PATCH V2] mm/cma: using per-CMA locks to improve concurrent allocation performance

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 10 Feb 2025 09:56:06 +0800 yangge1116@126.com wrote:

> From: yangge <yangge1116@126.com>
> 
> 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.

This patch was in and out of mm-unstable for a while, as Frank's series
"hugetlb/CMA improvements for large systems" was being added and
dropped.

Consequently it hasn't received any testing for a while.

Below is the version which I've now re-added to mm-unstable.  Can
you please check this and retest it?

Thanks.

From: Ge Yang <yangge1116@126.com>
Subject: mm/cma: using per-CMA locks to improve concurrent allocation performance
Date: Mon, 10 Feb 2025 09:56:06 +0800

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 solve 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.

Link: https://lkml.kernel.org/r/1739152566-744-1-git-send-email-yangge1116@126.com
Signed-off-by: Ge Yang <yangge1116@126.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Aisheng Dong <aisheng.dong@nxp.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/cma.c |    7 ++++---
 mm/cma.h |    1 +
 2 files changed, 5 insertions(+), 3 deletions(-)

--- a/mm/cma.c~mm-cma-using-per-cma-locks-to-improve-concurrent-allocation-performance
+++ a/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(str
 
 	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 *c
 		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;
--- a/mm/cma.h~mm-cma-using-per-cma-locks-to-improve-concurrent-allocation-performance
+++ a/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;
_