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Date: Thu, 29 May 2014 15:22:34 +0900 From: Joonsoo Kim <iamjoonsoo.kim@....com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Zhang Yanfei <zhangyanfei.yes@...il.com>, Johannes Weiner <hannes@...xchg.org>, Andi Kleen <andi@...stfloor.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Richard Yao <ryao@...too.org>, Joonsoo Kim <iamjoonsoo.kim@....com> Subject: [PATCH] vmalloc: use rcu list iterator to reduce vmap_area_lock contention 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@...too.org> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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