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Message-Id: <20250317204325.99b45373023ad2f901c1152e@linux-foundation.org>
Date: Mon, 17 Mar 2025 20:43:25 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: yangge1116@....com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 21cnbao@...il.com,
david@...hat.com, baolin.wang@...ux.alibaba.com, aisheng.dong@....com,
liuzixing@...on.cn
Subject: Re: [PATCH V2] mm/cma: using per-CMA locks to improve concurrent
allocation performance
On Mon, 10 Feb 2025 09:56:06 +0800 yangge1116@....com wrote:
> From: yangge <yangge1116@....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@....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@....com>
Reviewed-by: Barry Song <baohua@...nel.org>
Acked-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Oscar Salvador <osalvador@...e.de>
Cc: Aisheng Dong <aisheng.dong@....com>
Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@...ux-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;
_
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