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

[Oscar Salvador]

On Mon, Feb 10, 2025 at 09:56:06AM +0800, yangge1116@xxxxxxx wrote:
> From: yangge <yangge1116@xxxxxxx>
> 
> 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@xxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>


-- 
Oscar Salvador
SUSE Labs