mm/readahead.c: simplify get_next_ra_size()

mainline inclusion
from mainline-5.0-rc1
commit 20ff1c950500380c6f74ec1a0d6f4eafab673ef6
category: bugfix
bugzilla: 5928
CVE: NA

-----------------------------

It's a trivial simplification for get_next_ra_size() and clear enough for
humans to understand.

It also fixes potential overflow if ra->size(< ra_pages) is too large.

Link: http://lkml.kernel.org/r/1540707206-19649-1-git-send-email-hsiangkao@aol.comSigned-off-by: NGao Xiang <hsiangkao@aol.com>
Reviewed-by: NFengguang Wu <fengguang.wu@intel.com>
Reviewed-by: NMatthew Wilcox <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NJing xiangfeng <jingxiangfeng@huawei.com>
Reviewed-by: NChen Wandun <chenwandun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/readahead.c

@@ -275,14 +275,12 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
 				      unsigned long max)
 {
 	unsigned long cur = ra->size;
-	unsigned long newsize;
 
 	if (cur < max / 16)
-		newsize = 4 * cur;
-	else
-		newsize = 2 * cur;
-
-	return min(newsize, max);
+		return 4 * cur;
+	if (cur <= max / 2)
+		return 2 * cur;
+	return max;
 }
 
 /*