From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f50.google.com (mail-pb0-f50.google.com [209.85.160.50]) by kanga.kvack.org (Postfix) with ESMTP id 544616B0134 for ; Tue, 10 Jun 2014 22:15:17 -0400 (EDT) Received: by mail-pb0-f50.google.com with SMTP id rp16so1450482pbb.37 for ; Tue, 10 Jun 2014 19:15:17 -0700 (PDT) Received: from lgeamrelo02.lge.com (lgeamrelo02.lge.com. [156.147.1.126]) by mx.google.com with ESMTP id mn6si36370089pbc.17.2014.06.10.19.15.15 for ; Tue, 10 Jun 2014 19:15:16 -0700 (PDT) From: Joonsoo Kim Subject: [PATCH v2] vmalloc: use rcu list iterator to reduce vmap_area_lock contention Date: Wed, 11 Jun 2014 11:19:06 +0900 Message-Id: <1402453146-10057-1-git-send-email-iamjoonsoo.kim@lge.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Zhang Yanfei , Johannes Weiner , Andi Kleen , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Richard Yao , Eric Dumazet , Joonsoo Kim 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(). rcu can be used in this function because all RCU protocol is already respected by writers, since Nick Piggin commit db64fe02258f1507e13fe5 ("mm: rewrite vmap layer") back in linux-2.6.28 Specifically : insertions use list_add_rcu(), deletions use list_del_rcu() and kfree_rcu(). Note the rb tree is not used from rcu reader (it would not be safe), only the vmap_area_list has full RCU protection. Note that __purge_vmap_area_lazy() already uses this rcu protection. rcu_read_lock(); list_for_each_entry_rcu(va, &vmap_area_list, list) { if (va->flags & VM_LAZY_FREE) { if (va->va_start < *start) *start = va->va_start; if (va->va_end > *end) *end = va->va_end; nr += (va->va_end - va->va_start) >> PAGE_SHIFT; list_add_tail(&va->purge_list, &valist); va->flags |= VM_LAZY_FREEING; va->flags &= ~VM_LAZY_FREE; } } rcu_read_unlock(); v2: add more commit description from Eric [edumazet@google.com: add more commit description] Reported-by: Richard Yao Acked-by: Eric Dumazet Signed-off-by: Joonsoo Kim 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org