linux-kernel - [PATCH] mm/hotplug: Optimize clear_hwpoisoned

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Date:   Fri,  2 Nov 2018 23:00:01 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     akpm@...ux-foundation.org
Cc:     mhocko@...e.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Balbir Singh <bsingharora@...il.com>
Subject: [PATCH] mm/hotplug: Optimize clear_hwpoisoned_pages

In hot remove, we try to clear poisoned pages, but
a small optimization to check if num_poisoned_pages
is 0 helps remove the iteration through nr_pages.

Signed-off-by: Balbir Singh <bsingharora@...il.com>
---
 mm/sparse.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/sparse.c b/mm/sparse.c
index 33307fc05c4d..16219c7ddb5f 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -724,6 +724,16 @@ static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
 	if (!memmap)
 		return;
 
+	/*
+	 * A further optimization is to have per section
+	 * ref counted num_poisoned_pages, but that is going
+	 * to need more space per memmap, for now just do
+	 * a quick global check, this should speed up this
+	 * routine in the absence of bad pages.
+	 */
+	if (atomic_long_read(&num_poisoned_pages) == 0)
+		return;
+
 	for (i = 0; i < nr_pages; i++) {
 		if (PageHWPoison(&memmap[i])) {
 			atomic_long_sub(1, &num_poisoned_pages);
-- 
2.17.1