ocfs2: Allow smaller allocations during large writes

The ocfs2 write code loops through a page much like the block code, except
that ocfs2 allocation units can be any size, including larger than page
size. Typically it's equal to or larger than page size - most kernels run 4k
pages, the minimum ocfs2 allocation (cluster) size.

Some changes introduced during 2.6.23 changed the way writes to pages are
handled, and inadvertantly broke support for > 4k page size. Instead of just
writing one cluster at a time, we now handle the whole page in one pass.

This means that multiple (small) seperate allocations might happen in the
same pass. The allocation code howver typically optimizes by getting the
maximum which was reserved. This triggered a BUG_ON in the extend code where
it'd ask for a single bit (for one part of a > 4k page) and get back more
than it asked for.

Fix this by providing a variant of the high level allocation function which
allows the caller to specify a maximum. The traditional function remains and
just calls the new one with a maximum determined from the initial
reservation.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/fs/ocfs2/suballoc.h b/fs/ocfs2/suballoc.h
index f212dc01a84b..cafe93703095 100644
--- a/fs/ocfs2/suballoc.h
+++ b/fs/ocfs2/suballoc.h
@@ -85,6 +85,17 @@ int ocfs2_claim_clusters(struct ocfs2_super *osb,
                          u32 min_clusters,
                          u32 *cluster_start,
                          u32 *num_clusters);
+/*
+ * Use this variant of ocfs2_claim_clusters to specify a maxiumum
+ * number of clusters smaller than the allocation reserved.
+ */
+int __ocfs2_claim_clusters(struct ocfs2_super *osb,
+                           handle_t *handle,
+                           struct ocfs2_alloc_context *ac,
+                           u32 min_clusters,
+                           u32 max_clusters,
+                           u32 *cluster_start,
+                           u32 *num_clusters);
 
 int ocfs2_free_suballoc_bits(handle_t *handle,
                              struct inode *alloc_inode,