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Message-ID: <09057869-eb32-45dd-a7a1-9b7e1850eb11@126.com>
Date: Tue, 18 Mar 2025 15:21:42 +0800
From: Ge Yang <yangge1116@....com>
To: Andrew Morton <akpm@...ux-foundation.org>
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
在 2025/3/18 11:43, Andrew Morton 写道:
> 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?
Based on the latest mm-unstable code, after applying the patch and
conducting tests, it works normally. Thanks.
>
> 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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