[PATCH] vmalloc: Use atomic_long_add_return_relaxed()

Uladzislau Rezki (Sony)
2025-04-15T11:26:50Z

Switch from the atomic_long_add_return() to its relaxed version.

We do not need a full memory barrier or any memory ordering during
increasing the "vmap_lazy_nr" variable. What we only need is to do it
atomically. This is what atomic_long_add_return_relaxed() guarantees.

AARCH64:

<snip>
Default:
40ec: d34cfe94 lsr x20, x20, #12
40f0: 14000044 b 4200 <free_vmap_area_noflush+0x19c>
40f4: 94000000 bl 0 <__sanitizer_cov_trace_pc>
40f8: 90000000 adrp x0, 0 <__traceiter_alloc_vmap_area>
40fc: 91000000 add x0, x0, #0x0
4100: f8f40016 ldaddal x20, x22, [x0]
4104: 8b160296 add x22, x20, x22

Relaxed:
40ec: d34cfe94 lsr x20, x20, #12
40f0: 14000044 b 4200 <free_vmap_area_noflush+0x19c>
40f4: 94000000 bl 0 <__sanitizer_cov_trace_pc>
40f8: 90000000 adrp x0, 0 <__traceiter_alloc_vmap_area>
40fc: 91000000 add x0, x0, #0x0
4100: f8340016 ldadd x20, x22, [x0]
4104: 8b160296 add x22, x20, x22
<snip>

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
mm/vmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 7bb32f498d39..9d4027041a3f 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2370,7 +2370,7 @@ static void free_vmap_area_noflush(struct vmap_area *va)
if (WARN_ON_ONCE(!list_empty(&va->list)))
return;

- nr_lazy = atomic_long_add_return(va_size(va) >> PAGE_SHIFT,
+ nr_lazy = atomic_long_add_return_relaxed(va_size(va) >> PAGE_SHIFT,
&vmap_lazy_nr);

/*
--
2.39.5