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linux/mm/cma.h
Ge Yang 24ac6fb6e3 mm/cma: using per-CMA locks to improve concurrent allocation performance 
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>
2025-03-21 22:03:10 -07:00

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