[PATCH 2/6] btrfs: Use unified stripe_page's index calculation

From: Zhaolei <zhaolei@cn.fujitsu.com>
To: <linux-btrfs@vger.kernel.org>
Cc: Zhao Lei <zhaolei@cn.fujitsu.com>
Subject: [PATCH 2/6] btrfs: Use unified stripe_page's index calculation
Date: Thu, 5 Mar 2015 02:41:08 +0800	[thread overview]
Message-ID: <337fbe9ed9d9ddb47415b260e213e01c040d1ef3.1425494151.git.zhaolei@cn.fujitsu.com> (raw)
In-Reply-To: <86557aad51883ada25ace853f10d1474e8db048e.1425494151.git.zhaolei@cn.fujitsu.com>

From: Zhao Lei <zhaolei@cn.fujitsu.com>

We are using different index calculation method for stripe_page in
current code:
1: (rbio->stripe_len / PAGE_CACHE_SIZE) * stripe_index + page_index
2: DIV_ROUND_UP(rbio->stripe_len, PAGE_CACHE_SIZE) * stripe_index + page_index
3: DIV_ROUND_UP(rbio->stripe_len * stripe_index, PAGE_CACHE_SIZE) + page_index
...

They can get same result when stripe_len align to PAGE_CACHE_SIZE,
this is why current code can work.
But anyway, we need to fix it to make code better.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 fs/btrfs/raid56.c | 43 +++++++++++++++++++++----------------------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 0cfbfcf..645bc37 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -612,13 +612,28 @@ static int rbio_can_merge(struct btrfs_raid_bio *last,
 	return 1;
 }
 
+static int rbio_stripe_page_index(struct btrfs_raid_bio *rbio, int stripe,
+				  int index)
+{
+	return stripe * rbio->stripe_npages + index;
+}
+
+/*
+ * these are just the pages from the rbio array, not from anything
+ * the FS sent down to us
+ */
+static struct page *rbio_stripe_page(struct btrfs_raid_bio *rbio, int stripe,
+				     int index)
+{
+	return rbio->stripe_pages[rbio_stripe_page_index(rbio, stripe, index)];
+}
+
 /*
  * helper to index into the pstripe
  */
 static struct page *rbio_pstripe_page(struct btrfs_raid_bio *rbio, int index)
 {
-	index += (rbio->nr_data * rbio->stripe_len) >> PAGE_CACHE_SHIFT;
-	return rbio->stripe_pages[index];
+	return rbio_stripe_page(rbio, rbio->nr_data, index);
 }
 
 /*
@@ -629,10 +644,7 @@ static struct page *rbio_qstripe_page(struct btrfs_raid_bio *rbio, int index)
 {
 	if (rbio->nr_data + 1 == rbio->real_stripes)
 		return NULL;
-
-	index += ((rbio->nr_data + 1) * rbio->stripe_len) >>
-		PAGE_CACHE_SHIFT;
-	return rbio->stripe_pages[index];
+	return rbio_stripe_page(rbio, rbio->nr_data + 1, index);
 }
 
 /*
@@ -944,8 +956,7 @@ static struct page *page_in_rbio(struct btrfs_raid_bio *rbio,
  */
 static unsigned long rbio_nr_pages(unsigned long stripe_len, int nr_stripes)
 {
-	unsigned long nr = stripe_len * nr_stripes;
-	return DIV_ROUND_UP(nr, PAGE_CACHE_SIZE);
+	return DIV_ROUND_UP(stripe_len, PAGE_CACHE_SIZE) * nr_stripes;
 }
 
 /*
@@ -1023,13 +1034,13 @@ static int alloc_rbio_pages(struct btrfs_raid_bio *rbio)
 	return 0;
 }
 
-/* allocate pages for just the p/q stripes */
+/* only allocate pages for p/q stripes */
 static int alloc_rbio_parity_pages(struct btrfs_raid_bio *rbio)
 {
 	int i;
 	struct page *page;
 
-	i = (rbio->nr_data * rbio->stripe_len) >> PAGE_CACHE_SHIFT;
+	i = rbio_stripe_page_index(rbio, rbio->nr_data, 0);
 
 	for (; i < rbio->nr_pages; i++) {
 		if (rbio->stripe_pages[i])
@@ -1119,18 +1130,6 @@ static void validate_rbio_for_rmw(struct btrfs_raid_bio *rbio)
 }
 
 /*
- * these are just the pages from the rbio array, not from anything
- * the FS sent down to us
- */
-static struct page *rbio_stripe_page(struct btrfs_raid_bio *rbio, int stripe, int page)
-{
-	int index;
-	index = stripe * (rbio->stripe_len >> PAGE_CACHE_SHIFT);
-	index += page;
-	return rbio->stripe_pages[index];
-}
-
-/*
  * helper function to walk our bio list and populate the bio_pages array with
  * the result.  This seems expensive, but it is faster than constantly
  * searching through the bio list as we setup the IO in finish_rmw or stripe
-- 
1.8.5.1

