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

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Message-ID: <24ca760c-a861-4797-a434-d91a59513b12@redhat.com>
Date: Tue, 18 Mar 2025 14:02:21 +0100
From: David Hildenbrand <david@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>, yangge1116@....com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 21cnbao@...il.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 18.03.25 04:43, Andrew Morton wrote:
> 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>

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb