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.

[akpm@linux-foundation.org: tweak comment text]
Link: http://lkml.kernel.org/r/20181102120001.4526-1-bsingharora@gmail.com
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/sparse.c b/mm/sparse.c
index 3abc8cc..691544a 100644 (file)
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -740,6 +740,15 @@ static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
        if (!memmap)
                return;
 
+       /*
+        * A further optimization is to have per section refcounted
+        * num_poisoned_pages.  But that would need more space per memmap, so
+        * for now just do a quick global check to 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);