Messages in this thread Patch in this message | | | Subject | Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data" | From | Lin Ming <> | Date | Thu, 26 Sep 2013 00:02:24 +0800 |
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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 <peter@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 <minggr@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 <minggr@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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