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

[David Hildenbrand]

On 18.03.25 04:43, Andrew Morton wrote:
> On Mon, 10 Feb 2025 09:56:06 +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.
>
> 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@xxxxxxx>
> 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@xxxxxxx
> Signed-off-by: Ge Yang <yangge1116@xxxxxxx>
> Reviewed-by: Barry Song <baohua@xxxxxxxxxx>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Aisheng Dong <aisheng.dong@xxxxxxx>
> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb