On Marvell berlin arm64 platforms, I see the preemptoff tracer report a max 26543 us latency at __purge_vmap_area_lazy, this latency is an awfully bad for STB. And the ftrace log also shows __free_vmap_area contributes most latency now. I noticed that Joel mentioned the same issue[1] on x86 platform and gave two solutions, but it seems no patch is sent out for this purpose.
This patch adopts Joel's first solution, but I use 16MB per core rather than 8MB per core for the number of lazy_max_pages. After this patch, the preemptoff tracer reports a max 6455us latency, reduced to 1/4 of original result. [1] http://lkml.iu.edu/hypermail/linux/kernel/1603.2/04803.html Signed-off-by: Jisheng Zhang <jszh...@marvell.com> --- mm/vmalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 91f44e7..66f377a 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -596,7 +596,7 @@ static unsigned long lazy_max_pages(void) log = fls(num_online_cpus()); - return log * (32UL * 1024 * 1024 / PAGE_SIZE); + return log * (16UL * 1024 * 1024 / PAGE_SIZE); } static atomic_t vmap_lazy_nr = ATOMIC_INIT(0); -- 2.9.3
