From 12720557095321254db83fdc44167581ab7249d3 Mon Sep 17 00:00:00 2001
From: Jeff Moyer <jmoyer@redhat.com>
Date: Tue, 15 Dec 2009 16:47:49 -0800
Subject: [PATCH] --- yaml --- r: 176711 b: refs/heads/master c:
 23aee091d804efa8cc732a31c1ae5d625e1ec886 h: refs/heads/master i:   176709:
 a44892f48e57251c4672775fbafe8f8d13fb6fac   176707:
 236428e1ee81663e758792ac91280310495e6c23   176703:
 213bff6f7d5c4aff0146aa1d7470a29f0ccd8d9d v: v3

---
 [refs]               |  2 +-
 trunk/fs/direct-io.c | 38 +++++++++++++++++++++++++-------------
 2 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/[refs] b/[refs]
index 4206165a9ab1..5047551d53a9 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: fac046ad0b1ee2c4244ebf43a26433ef0ea29ae4
+refs/heads/master: 23aee091d804efa8cc732a31c1ae5d625e1ec886
diff --git a/trunk/fs/direct-io.c b/trunk/fs/direct-io.c
index b912270942fa..9f34bb9b1ecb 100644
--- a/trunk/fs/direct-io.c
+++ b/trunk/fs/direct-io.c
@@ -104,6 +104,18 @@ struct dio {
 	unsigned cur_page_len;		/* Nr of bytes at cur_page_offset */
 	sector_t cur_page_block;	/* Where it starts */
 
+	/* BIO completion state */
+	spinlock_t bio_lock;		/* protects BIO fields below */
+	unsigned long refcount;		/* direct_io_worker() and bios */
+	struct bio *bio_list;		/* singly linked via bi_private */
+	struct task_struct *waiter;	/* waiting task (NULL if none) */
+
+	/* AIO related stuff */
+	struct kiocb *iocb;		/* kiocb */
+	int is_async;			/* is IO async ? */
+	int io_error;			/* IO error in completion path */
+	ssize_t result;                 /* IO result */
+
 	/*
 	 * Page fetching state. These variables belong to dio_refill_pages().
 	 */
@@ -115,22 +127,16 @@ struct dio {
 	 * Page queue.  These variables belong to dio_refill_pages() and
 	 * dio_get_page().
 	 */
-	struct page *pages[DIO_PAGES];	/* page buffer */
 	unsigned head;			/* next page to process */
 	unsigned tail;			/* last valid page + 1 */
 	int page_errors;		/* errno from get_user_pages() */
 
-	/* BIO completion state */
-	spinlock_t bio_lock;		/* protects BIO fields below */
-	unsigned long refcount;		/* direct_io_worker() and bios */
-	struct bio *bio_list;		/* singly linked via bi_private */
-	struct task_struct *waiter;	/* waiting task (NULL if none) */
-
-	/* AIO related stuff */
-	struct kiocb *iocb;		/* kiocb */
-	int is_async;			/* is IO async ? */
-	int io_error;			/* IO error in completion path */
-	ssize_t result;                 /* IO result */
+	/*
+	 * pages[] (and any fields placed after it) are not zeroed out at
+	 * allocation time.  Don't add new fields after pages[] unless you
+	 * wish that they not be zeroed.
+	 */
+	struct page *pages[DIO_PAGES];	/* page buffer */
 };
 
 /*
@@ -1151,10 +1157,16 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 		}
 	}
 
-	dio = kzalloc(sizeof(*dio), GFP_KERNEL);
+	dio = kmalloc(sizeof(*dio), GFP_KERNEL);
 	retval = -ENOMEM;
 	if (!dio)
 		goto out;
+	/*
+	 * Believe it or not, zeroing out the page array caused a .5%
+	 * performance regression in a database benchmark.  So, we take
+	 * care to only zero out what's needed.
+	 */
+	memset(dio, 0, offsetof(struct dio, pages));
 
 	/*
 	 * For block device access DIO_NO_LOCKING is used,