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

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Message-ID: <Z6nDmznSoFNDlsvU@localhost.localdomain>
Date: Mon, 10 Feb 2025 10:15:07 +0100
From: Oscar Salvador <osalvador@...e.de>
To: yangge1116@....com
Cc: akpm@...ux-foundation.org, 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, Feb 10, 2025 at 09:56:06AM +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.
> 
> Signed-off-by: yangge <yangge1116@....com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>


-- 
Oscar Salvador
SUSE Labs