From patchwork Sat Mar  5 16:50:14 2011
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Date: Sat, 5 Mar 2011 10:50:14 -0600
Message-ID: <AANLkTi=gqurEsoMZv+10Np4duOKq4kZf77mTgu6BfkSC@mail.gmail.com>
Subject: Re: [PATCH] btrfs file write debugging patch
From: Mitch Harder <mitch.harder@sabayonlinux.org>
To: Xin Zhong <thierryzhong@hotmail.com>
Cc: chris.mason@oracle.com, xin.zhong@intel.com, linux-btrfs@vger.kernel.org
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--- fs/btrfs/file.c	2011-03-05 07:34:43.025131607 -0600
+++ /usr/src/linux/fs/btrfs/file.c	2011-03-05 07:41:45.001260294 -0600
@@ -1023,8 +1023,20 @@

 		copied = btrfs_copy_from_user(pos, num_pages,
 					   write_bytes, pages, &i);
-		dirty_pages = (copied + offset + PAGE_CACHE_SIZE - 1) >>
-				PAGE_CACHE_SHIFT;
+
+		/*
+		 * if we have trouble faulting in the pages, fall
+		 * back to one page at a time
+		 */
+		if (copied < write_bytes)
+			nrptrs = 1;
+
+		if (copied == 0)
+			dirty_pages = 0;
+		else
+			dirty_pages = (copied + offset +
+				       PAGE_CACHE_SIZE - 1) >>
+				       PAGE_CACHE_SHIFT;

 		if (num_pages > dirty_pages) {
 			if (copied > 0)