[PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency

From	Jisheng Zhang <jszhang@marvell.com>
Newsgroups	linux.kernel
Subject	[PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency
Date	2016-09-29 09:40 +0200
Message-ID	<smE6K-10y-13@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

Show all headers | View raw

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 <jszhang@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

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

[PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency Jisheng Zhang <jszhang@marvell.com> - 2016-09-29 09:40 +0200
  Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to  reduce latency Chris Wilson <chris@chris-wilson.co.uk> - 2016-09-29 10:20 +0200
    Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to  reduce latency Jisheng Zhang <jszhang@marvell.com> - 2016-09-29 10:40 +0200
      Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to  reduce latency Chris Wilson <chris@chris-wilson.co.uk> - 2016-09-29 13:10 +0200
        Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to  reduce latency Jisheng Zhang <jszhang@marvell.com> - 2016-09-29 13:30 +0200
    Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency Joel Fernandes <agnel.joel@gmail.com> - 2016-10-09 05:50 +0200
      Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to  reduce latency Chris Wilson <chris@chris-wilson.co.uk> - 2016-10-09 14:50 +0200
        Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency Joel Fernandes <joel.opensrc@gmail.com> - 2016-10-09 21:10 +0200
          Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to  reduce latency Chris Wilson <chris@chris-wilson.co.uk> - 2016-10-09 21:30 +0200
            Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency Joel Fernandes <agnel.joel@gmail.com> - 2016-10-11 07:10 +0200
              Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency Joel Fernandes <agnel.joel@gmail.com> - 2016-10-11 07:40 +0200

csiph-web