linux-kernel - [PATCH] mm/mmap.c: optimization of do_mmap

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Date:	Sat,  6 Jun 2015 11:54:32 +0200
From:	Piotr Kwapulinski <kwapulinski.piotr@...il.com>
To:	akpm@...ux-foundation.org
Cc:	kirill.shutemov@...ux.intel.com, riel@...hat.com, mhocko@...e.cz,
	sasha.levin@...cle.com, dave@...olabs.net, koct9i@...il.com,
	pfeiner@...gle.com, dh.herrmann@...il.com, vishnu.ps@...sung.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Piotr Kwapulinski <kwapulinski.piotr@...il.com>
Subject: [PATCH] mm/mmap.c: optimization of do_mmap_pgoff function

The simple check for zero length memory mapping may be performed
earlier. It causes that in case of zero length memory mapping some
unnecessary code is not executed at all. It does not make the code less
readable and saves some CPU cycles.

Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@...il.com>
---
 mm/mmap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index bb50cac..aa632ad 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1258,6 +1258,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 
 	*populate = 0;
 
+	if (!len)
+		return -EINVAL;
+
 	/*
 	 * Does the application expect PROT_READ to imply PROT_EXEC?
 	 *
@@ -1268,9 +1271,6 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 		if (!(file && (file->f_path.mnt->mnt_flags & MNT_NOEXEC)))
 			prot |= PROT_EXEC;
 
-	if (!len)
-		return -EINVAL;
-
 	if (!(flags & MAP_FIXED))
 		addr = round_hint_to_min(addr);
 
-- 
2.3.7

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