On Wed, 2013-09-25 at 07:30 -0400, Peter Hurley wrote:
> On 09/25/2013 05:04 AM, Lin Ming wrote:
> > On Wed, Sep 18, 2013 at 8:22 AM, Peter Hurley <pe...@hurleysoftware.com>
> > wrote:
> > [snip]
> >>
> >> Looking over vmalloc.c, the critical section footprint of the
> >> vmap_area_lock
> >> could definitely be reduced (even nearly eliminated), but that's a project
> >> for
> >> another day :)
> >
> > Hi Peter,
> >
> > I also looked over vmallo.c, but didn't find obvious way to reduce the
> > critical section footprint.
> > Could you share some hints how to do this?
>
> vmap_area_list is an RCU list.
> get_vmalloc_info() doesn't need to take the vmap_area_lock at all.
> Look at __purge_vmap_area_lazy() for a howto.
Would you like below patch?
From: Lin Ming <min...@gmail.com>
Date: Wed, 25 Sep 2013 23:48:19 +0800
Subject: [PATCH] mm/vmalloc.c: eliminate vmap_area_lock in get_vmalloc_info()
vmap_area_list is an RCU list.
get_vmalloc_info() doesn't need to take the vmap_area_lock at all.
Use RCU to protect list scan.
Signed-off-by: Lin Ming <min...@gmail.com>
---
mm/vmalloc.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 13a5495..4523c9c 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2684,14 +2684,14 @@ 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;
/*
@@ -2718,7 +2718,7 @@ 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
--
1.7.2.5
>
> Regards,
> Peter Hurley
>
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