Re: [PATCH] nfs: fix NR_FILE_DIRTY underflow

Re: [PATCH] nfs: fix NR_FILE_DIRTY underflow

[Peter Zijlstra]

- Sorry for possible duplicates, but I don't seem to be getting to lkml -

On Wed, 2006-12-13 at 07:26 -0500, Trond Myklebust wrote:
> On Wed, 2006-12-13 at 13:12 +0100, Peter Zijlstra wrote:
> > Still testing this patch, but it looks good so far.
> > 
> > ---
> > Just setting PG_dirty can cause NR_FILE_DIRTY to underflow
> > which is bad (TM).
> > 
> > Use set_page_dirty() which will do the right thing.
> 
> Actually, I'd prefer to have it do the right thing by getting rid of
> that call to test_clear_page_dirty() inside
> invalidate_inode_pages2_range(). That is causing loss of data integrity,
> and is what is causing us to have to hack NFS in the first place.

Ah, I think I see what your problem is there.
How about this totally untested patch:

  (little update - it seems to compile and run, now testing if it fixes
the problem too)

---
Delay clearing the dirty page state till after removing it from the
mapping in invalidate_inode_pages2_range(). This will give
try_to_release_pages() a shot to flush dirty data.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 fs/nfs/file.c              |    2 --
 include/linux/page-flags.h |    2 ++
 mm/page-writeback.c        |   17 +++++++++++------
 mm/truncate.c              |   11 +++--------
 4 files changed, 16 insertions(+), 16 deletions(-)

Index: linux-2.6-git/fs/nfs/file.c
===================================================================
--- linux-2.6-git.orig/fs/nfs/file.c	2006-12-13 15:31:26.000000000 +0100
+++ linux-2.6-git/fs/nfs/file.c	2006-12-13 15:39:33.000000000 +0100
@@ -320,8 +320,6 @@ static int nfs_release_page(struct page 
 	 */
 	if (!(gfp & __GFP_FS))
 		return 0;
-	/* Hack... Force nfs_wb_page() to write out the page */
-	SetPageDirty(page);
 	return !nfs_wb_page(page_file_mapping(page)->host, page);
 }
 
Index: linux-2.6-git/include/linux/page-flags.h
===================================================================
--- linux-2.6-git.orig/include/linux/page-flags.h	2006-12-13 15:35:50.000000000 +0100
+++ linux-2.6-git/include/linux/page-flags.h	2006-12-13 15:36:14.000000000 +0100
@@ -252,7 +252,9 @@ static inline void SetPageUptodate(struc
 #define ClearPageUncached(page)	clear_bit(PG_uncached, &(page)->flags)
 
 struct page;	/* forward declaration */
+struct address_space;
 
+int __test_clear_page_dirty(struct address_space *mapping, struct page *page);
 int test_clear_page_dirty(struct page *page);
 int test_clear_page_writeback(struct page *page);
 int test_set_page_writeback(struct page *page);
Index: linux-2.6-git/mm/page-writeback.c
===================================================================
--- linux-2.6-git.orig/mm/page-writeback.c	2006-12-13 15:34:15.000000000 +0100
+++ linux-2.6-git/mm/page-writeback.c	2006-12-13 15:39:41.000000000 +0100
@@ -850,13 +850,8 @@ int set_page_dirty_lock(struct page *pag
 }
 EXPORT_SYMBOL(set_page_dirty_lock);
 
-/*
- * Clear a page's dirty flag, while caring for dirty memory accounting. 
- * Returns true if the page was previously dirty.
- */
-int test_clear_page_dirty(struct page *page)
+int __test_clear_page_dirty(struct address_space *mapping, struct page *page)
 {
-	struct address_space *mapping = page_mapping(page);
 	unsigned long flags;
 
 	if (!mapping)
@@ -880,6 +875,16 @@ int test_clear_page_dirty(struct page *p
 	write_unlock_irqrestore(&mapping->tree_lock, flags);
 	return 0;
 }
+
+/*
+ * Clear a page's dirty flag, while caring for dirty memory accounting.
+ * Returns true if the page was previously dirty.
+ */
+int test_clear_page_dirty(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+	return __test_clear_page_dirty(mapping, page);
+}
 EXPORT_SYMBOL(test_clear_page_dirty);
 
 /*
Index: linux-2.6-git/mm/truncate.c
===================================================================
--- linux-2.6-git.orig/mm/truncate.c	2006-12-13 15:36:38.000000000 +0100
+++ linux-2.6-git/mm/truncate.c	2006-12-13 15:44:01.000000000 +0100
@@ -307,18 +307,12 @@ invalidate_complete_page2(struct address
 		return 0;
 
 	write_lock_irq(&mapping->tree_lock);
-	if (PageDirty(page))
-		goto failed;
-
 	BUG_ON(PagePrivate(page));
 	__remove_from_page_cache(page);
 	write_unlock_irq(&mapping->tree_lock);
 	ClearPageUptodate(page);
 	page_cache_release(page);	/* pagecache ref */
 	return 1;
-failed:
-	write_unlock_irq(&mapping->tree_lock);
-	return 0;
 }
 
 /**
@@ -386,12 +380,13 @@ int invalidate_inode_pages2_range(struct
 					  PAGE_CACHE_SIZE, 0);
 				}
 			}
-			was_dirty = test_clear_page_dirty(page);
+			was_dirty = PageDirty(page);
 			if (!invalidate_complete_page2(mapping, page)) {
 				if (was_dirty)
 					set_page_dirty(page);
 				ret = -EIO;
-			}
+			} else
+				__test_clear_page_dirty(mapping, page);
 			unlock_page(page);
 		}
 		pagevec_release(&pvec);


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