Re: 2.6.20-rc5: known unfixed regressions

[David Chinner <dgc@sgi.com>]

On Sat, Jan 13, 2007 at 08:11:25AM +0100, Adrian Bunk wrote:
> On Fri, Jan 12, 2007 at 02:27:48PM -0500, Linus Torvalds wrote:
> >...
> > A lot of developers (including me) will be gone next week for 
> > Linux.Conf.Au, so you have a week of rest and quiet to test this, and 
> > report any problems. 
> > 
> > Not that there will be any, right? You all behave now!
> >...
> 
> This still leaves the old regressions we have not yet fixed...
> 
> 
> This email lists some known regressions in 2.6.20-rc5 compared to 2.6.19.
> 
> 
> Subject    : BUG: at mm/truncate.c:60 cancel_dirty_page()  (XFS)
> References : http://lkml.org/lkml/2007/1/5/308
> Submitter  : Sami Farin <7atbggg02@sneakemail.com>
> Handled-By : David Chinner <dgc@sgi.com>
> Status     : problem is being discussed

I'm at LCA and been having laptop dramas so the fix is being held up at this
point. I and trying to test a change right now that adds an optional unmap
to truncate_inode_pages_range as XFS needs, in some circumstances, to toss
out dirty pages (with dirty bufferheads) and hence requires truncate semantics
that are currently missing unmap calls.

Semi-untested patch attached below.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group


 fs/xfs/linux-2.6/xfs_fs_subr.c |    6 ++--
 include/linux/mm.h             |    2 +
 mm/truncate.c                  |   60 ++++++++++++++++++++++++++++++++++++-----
 3 files changed, 60 insertions(+), 8 deletions(-)

Index: linux-2.6.19/fs/xfs/linux-2.6/xfs_fs_subr.c
===================================================================
--- linux-2.6.19.orig/fs/xfs/linux-2.6/xfs_fs_subr.c	2006-10-03 23:22:36.000000000 +1000
+++ linux-2.6.19/fs/xfs/linux-2.6/xfs_fs_subr.c	2007-01-17 01:24:51.771273750 +1100
@@ -32,7 +32,8 @@ fs_tosspages(
 	struct inode	*ip = vn_to_inode(vp);
 
 	if (VN_CACHED(vp))
-		truncate_inode_pages(ip->i_mapping, first);
+		truncate_unmap_inode_pages_range(ip->i_mapping,
+					     first, last, 1);
 }
 
 void
@@ -49,7 +50,8 @@ fs_flushinval_pages(
 		if (VN_TRUNC(vp))
 			VUNTRUNCATE(vp);
 		filemap_write_and_wait(ip->i_mapping);
-		truncate_inode_pages(ip->i_mapping, first);
+		truncate_unmap_inode_pages_range(ip->i_mapping,
+					     first, last, 1);
 	}
 }
 
Index: linux-2.6.19/include/linux/mm.h
===================================================================
--- linux-2.6.19.orig/include/linux/mm.h	2007-01-17 01:21:16.017790000 +1100
+++ linux-2.6.19/include/linux/mm.h	2007-01-17 01:24:51.775274000 +1100
@@ -1058,6 +1058,8 @@ extern unsigned long page_unuse(struct p
 extern void truncate_inode_pages(struct address_space *, loff_t);
 extern void truncate_inode_pages_range(struct address_space *,
 				       loff_t lstart, loff_t lend);
+extern void truncate_unmap_inode_pages_range(struct address_space *,
+				       loff_t lstart, loff_t lend, int unmap);
 
 /* generic vm_area_ops exported for stackable file systems */
 extern struct page *filemap_nopage(struct vm_area_struct *, unsigned long, int *);
Index: linux-2.6.19/mm/truncate.c
===================================================================
--- linux-2.6.19.orig/mm/truncate.c	2007-01-17 01:21:23.074231000 +1100
+++ linux-2.6.19/mm/truncate.c	2007-01-17 01:24:51.779274250 +1100
@@ -59,7 +59,7 @@ void cancel_dirty_page(struct page *page
 
 		WARN_ON(++warncount < 5);
 	}
-		
+
 	if (TestClearPageDirty(page)) {
 		struct address_space *mapping = page->mapping;
 		if (mapping && mapping_cap_account_dirty(mapping)) {
@@ -122,16 +122,34 @@ invalidate_complete_page(struct address_
 	return ret;
 }
 
+/*
+ * This is a helper for truncate_unmap_inode_page. Unmap the page we
+ * are passed. Page must be locked by the caller.
+ */
+static void
+unmap_single_page(struct address_space *mapping, struct page *page)
+{
+	BUG_ON(!PageLocked(page));
+	while (page_mapped(page)) {
+		unmap_mapping_range(mapping,
+			(loff_t)page->index << PAGE_CACHE_SHIFT,
+			PAGE_CACHE_SIZE, 0);
+	}
+}
+
 /**
- * truncate_inode_pages - truncate range of pages specified by start and
+ * truncate_unmap_inode_pages_range - truncate range of pages specified by
+ * start and end byte offsets and optionally unmap them first.
  * end byte offsets
  * @mapping: mapping to truncate
  * @lstart: offset from which to truncate
  * @lend: offset to which to truncate
+ * @unmap: unmap whole truncated pages if non-zero
  *
  * Truncate the page cache, removing the pages that are between
  * specified offsets (and zeroing out partial page
- * (if lstart is not page aligned)).
+ * (if lstart is not page aligned)). If specified, unmap the pages
+ * before they are removed.
  *
  * Truncate takes two passes - the first pass is nonblocking.  It will not
  * block on page locks and it will not block on writeback.  The second pass
@@ -146,8 +164,8 @@ invalidate_complete_page(struct address_
  * mapping is large, it is probably the case that the final pages are the most
  * recently touched, and freeing happens in ascending file offset order.
  */
-void truncate_inode_pages_range(struct address_space *mapping,
-				loff_t lstart, loff_t lend)
+void truncate_unmap_inode_pages_range(struct address_space *mapping,
+				loff_t lstart, loff_t lend, int unmap)
 {
 	const pgoff_t start = (lstart + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
 	pgoff_t end;
@@ -162,6 +180,14 @@ void truncate_inode_pages_range(struct a
 	BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));
 	end = (lend >> PAGE_CACHE_SHIFT);
 
+	/*
+	 * if unmapping, do a range unmap up front to minimise the
+	 * overhead of unmapping the pages
+	 */
+	if (unmap) {
+		unmap_mapping_range(mapping, (loff_t)start << PAGE_CACHE_SHIFT,
+					   (loff_t)end << PAGE_CACHE_SHIFT, 0);
+	}
 	pagevec_init(&pvec, 0);
 	next = start;
 	while (next <= end &&
@@ -184,6 +210,8 @@ void truncate_inode_pages_range(struct a
 				unlock_page(page);
 				continue;
 			}
+			if (unmap)
+				unmap_single_page(mapping, page);
 			truncate_complete_page(mapping, page);
 			unlock_page(page);
 		}
@@ -195,6 +223,8 @@ void truncate_inode_pages_range(struct a
 		struct page *page = find_lock_page(mapping, start - 1);
 		if (page) {
 			wait_on_page_writeback(page);
+			if (unmap)
+				unmap_single_page(mapping, page);
 			truncate_partial_page(page, partial);
 			unlock_page(page);
 			page_cache_release(page);
@@ -224,12 +254,30 @@ void truncate_inode_pages_range(struct a
 			if (page->index > next)
 				next = page->index;
 			next++;
+			if (unmap)
+				unmap_single_page(mapping, page);
 			truncate_complete_page(mapping, page);
 			unlock_page(page);
 		}
 		pagevec_release(&pvec);
 	}
 }
+EXPORT_SYMBOL(truncate_unmap_inode_pages_range);
+
+/**
+ * truncate_inode_pages_range - truncate range of pages specified by start and
+ * end byte offsets
+ * @mapping: mapping to truncate
+ * @lstart: offset from which to truncate
+ * @lend: offset to which to truncate
+ *
+ * Called under (and serialised by) inode->i_mutex.
+ */
+void truncate_inode_pages_range(struct address_space *mapping,
+				loff_t lstart, loff_t lend)
+{
+	truncate_unmap_inode_pages_range(mapping, lstart, lend, 0);
+}
 EXPORT_SYMBOL(truncate_inode_pages_range);
 
 /**
@@ -241,7 +289,7 @@ EXPORT_SYMBOL(truncate_inode_pages_range
  */
 void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
 {
-	truncate_inode_pages_range(mapping, lstart, (loff_t)-1);
+	truncate_unmap_inode_pages_range(mapping, lstart, (loff_t)-1, 0);
 }
 EXPORT_SYMBOL(truncate_inode_pages);
 
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