From 16acea8215a0824879d2600f29edf66e63b4b506 Mon Sep 17 00:00:00 2001
From: Joseph Qi <joseph.qi@linux.alibaba.com>
Date: Wed, 15 May 2019 16:55:24 +0800
Subject: [PATCH] block: introduce bvec_nth_page()

Cherry-pick from upstream commit 4d633062c1c0794a6b3836b7b55afba4599736e8.

Single-page bvec can often be seen in small BS workloads, so
introduce bvec_nth_page() for avoiding to call nth_page() unnecessarily,
which looks not cheap.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: Caspar Zhang <caspar@linux.alibaba.com>
---
 include/linux/bvec.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index fe7a22dd133b..66a737c6baa6 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/bug.h>
 #include <linux/errno.h>
+#include <linux/mm.h>
 
 /*
  * was unsigned short, but we might as well be ready for > 64kB I/O pages
@@ -46,6 +47,11 @@ struct bvec_iter {
 						   current bvec */
 };
 
+static inline struct page *bvec_nth_page(struct page *page, int idx)
+{
+	return idx == 0 ? page : nth_page(page, idx);
+}
+
 /*
  * various member access, note that bio_data should of course not be used
  * on highmem page vectors
-- 
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