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

[Ge Yang <yangge1116@126.com>]

在 2025/3/18 11:43, Andrew Morton 写道:
> 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?
Based on the latest mm-unstable code, after applying the patch and 
conducting tests, it works normally. Thanks.
> 
> 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;
> _