lkml.org 
[lkml]   [2014]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] vmalloc: use rcu list iterator to reduce vmap_area_lock contention
Date
I do not have a way of tracing it. I meant to reply when I did, but that has not changed. That being said, I like this patch.

On May 29, 2014, at 2:22 AM, Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote:

> Richard Yao reported a month ago that his system have a trouble
> with vmap_area_lock contention during performance analysis
> by /proc/meminfo. Andrew asked why his analysis checks /proc/meminfo
> stressfully, but he didn't answer it.
>
> https://lkml.org/lkml/2014/4/10/416
>
> Although I'm not sure that this is right usage or not, there is a solution
> reducing vmap_area_lock contention with no side-effect. That is just
> to use rcu list iterator in get_vmalloc_info(). This function only needs
> values on vmap_area structure, so we don't need to grab a spinlock.
>
> Reported-by: Richard Yao <ryao@gentoo.org>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index f64632b..fdbb116 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2690,14 +2690,14 @@ void get_vmalloc_info(struct vmalloc_info *vmi)
>
> prev_end = VMALLOC_START;
>
> - spin_lock(&vmap_area_lock);
> + rcu_read_lock();
>
> if (list_empty(&vmap_area_list)) {
> vmi->largest_chunk = VMALLOC_TOTAL;
> goto out;
> }
>
> - list_for_each_entry(va, &vmap_area_list, list) {
> + list_for_each_entry_rcu(va, &vmap_area_list, list) {
> unsigned long addr = va->va_start;
>
> /*
> @@ -2724,7 +2724,7 @@ void get_vmalloc_info(struct vmalloc_info *vmi)
> vmi->largest_chunk = VMALLOC_END - prev_end;
>
> out:
> - spin_unlock(&vmap_area_lock);
> + rcu_read_unlock();
> }
> #endif
>
> --
> 1.7.9.5
>


\
 
 \ /
  Last update: 2014-05-29 16:21    [W:0.206 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site