linux-kernel - Re: [patch] rewrite rd

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Date:	Tue, 4 Dec 2007 08:08:56 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, rob@...dley.net,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [patch] rewrite rd

On Tue, Dec 04, 2007 at 08:01:31AM +0100, Nick Piggin wrote:
> Thanks for the review, I'll post an incremental patch in a sec.
 

Index: linux-2.6/drivers/block/brd.c
===================================================================
--- linux-2.6.orig/drivers/block/brd.c
+++ linux-2.6/drivers/block/brd.c
@@ -56,7 +56,7 @@ struct brd_device {
  */
 static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
 {
-	unsigned long idx;
+	pgoff_t idx;
 	struct page *page;
 
 	/*
@@ -87,13 +87,17 @@ static struct page *brd_lookup_page(stru
  */
 static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
 {
-	unsigned long idx;
+	pgoff_t idx;
 	struct page *page;
 
 	page = brd_lookup_page(brd, sector);
 	if (page)
 		return page;
 
+	/*
+	 * Must use NOIO because we don't want to recurse back into the
+	 * block or filesystem layers from page reclaim.
+	 */
 	page = alloc_page(GFP_NOIO | __GFP_HIGHMEM | __GFP_ZERO);
 	if (!page)
 		return NULL;
@@ -148,6 +152,11 @@ static void brd_free_pages(struct brd_de
 
 		pos++;
 
+		/*
+		 * This assumes radix_tree_gang_lookup always returns as
+		 * many pages as possible. If the radix-tree code changes,
+		 * so will this have to.
+		 */
 	} while (nr_pages == FREE_BATCH);
 }
 
@@ -159,7 +168,7 @@ static int copy_to_brd_setup(struct brd_
 	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
 	size_t copy;
 
-	copy = min((unsigned long)n, PAGE_SIZE - offset);
+	copy = min_t(size_t, n, PAGE_SIZE - offset);
 	if (!brd_insert_page(brd, sector))
 		return -ENOMEM;
 	if (copy < n) {
@@ -181,7 +190,7 @@ static void copy_to_brd(struct brd_devic
 	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
 	size_t copy;
 
-	copy = min((unsigned long)n, PAGE_SIZE - offset);
+	copy = min_t(size_t, n, PAGE_SIZE - offset);
 	page = brd_lookup_page(brd, sector);
 	BUG_ON(!page);
 
@@ -213,7 +222,7 @@ static void copy_from_brd(void *dst, str
 	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
 	size_t copy;
 
-	copy = min((unsigned long)n, PAGE_SIZE - offset);
+	copy = min_t(size_t, n, PAGE_SIZE - offset);
 	page = brd_lookup_page(brd, sector);
 	if (page) {
 		src = kmap_atomic(page, KM_USER1);
@@ -318,6 +327,9 @@ static int brd_ioctl(struct inode *inode
 		/*
 		 * Invalidate the cache first, so it isn't written
 		 * back to the device.
+		 *
+		 * Another thread might instantiate more buffercache here,
+		 * but there is not much we can do to close that race.
 		 */
 		invalidate_bh_lrus();
 		truncate_inode_pages(bdev->bd_inode->i_mapping, 0);
--
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