xfs: convert big array and blob array to use memfd backendrepair-part-one_2019-02-04

There are several problems with the initial implementations of the big
array and the blob array data structures.  First, using linked lists
imposes a two-pointer overhead on every record stored.  For blobs this
isn't serious, but for fixed-size records this increases memory
requirements by 40-60%.  Second, we're using kernel memory to store the
intermediate records.  Kernel memory cannot be paged out, which means we
run the risk of OOMing the machine when we run out of physical memory.

Therefore, replace the linked lists in both structures with memfd files.
Random access becomes much easier, memory overhead drops to a negligible
amount, and because memfd pages can be swapped, we have considerably
more flexibility for memory use.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 3 insertions, 13 deletions

diff --git a/fs/xfs/scrub/array.h b/fs/xfs/scrub/array.h
index a6a7b69dc138..b1b473bc56c5 100644
--- a/fs/xfs/scrub/array.h
+++ b/fs/xfs/scrub/array.h
@@ -6,20 +6,10 @@
 #ifndef __XFS_SCRUB_ARRAY_H__
 #define __XFS_SCRUB_ARRAY_H__
 
-struct xma_item;
-
-struct xma_cache {
-	uint64_t	nr;
-	struct xa_item	*item;
-};
-
-#define XMA_CACHE_SIZE	(8)
-
 struct xfbma {
-	struct list_head	list;
-	size_t			obj_size;
-	uint64_t		nr;
-	struct xma_cache	cache[XMA_CACHE_SIZE];
+	struct file	*filp;
+	size_t		obj_size;
+	uint64_t	nr;
 };
 
 struct xfbma *xfbma_init(size_t obj_size);