xfs: simplify log item descriptor tracking

Currently we track log item descriptor belonging to a transaction using a
complex opencoded chunk allocator.  This code has been there since day one
and seems to work around the lack of an efficient slab allocator.

This patch replaces it with dynamically allocated log item descriptors
from a dedicated slab pool, linked to the transaction by a linked list.

This allows to greatly simplify the log item descriptor tracking to the
point where it's just a couple hundred lines in xfs_trans.c instead of
a separate file.  The external API has also been simplified while we're
at it - the xfs_trans_add_item and xfs_trans_del_item functions to add/
delete items from a transaction have been simplified to the bare minium,
and the xfs_trans_find_item function is replaced with a direct dereference
of the li_desc field.  All debug code walking the list of log items in
a transaction is down to a simple list_for_each_entry.

Note that we could easily use a singly linked list here instead of the
double linked list from list.h as the fastpath only does deletion from
sequential traversal.  But given that we don't have one available as
a library function yet I use the list.h functions for simplicity.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

1 files changed, 7 insertions, 98 deletions

diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index e639e8e..0c903eb 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -161,105 +161,14 @@ typedef struct xfs_trans_header {
  * the amount of space needed to log the item it describes
  * once we get to commit processing (see xfs_trans_commit()).
  */
-typedef struct xfs_log_item_desc {
+struct xfs_log_item_desc {
 	struct xfs_log_item	*lid_item;
-	ushort		lid_size;
-	unsigned char	lid_flags;
-	unsigned char	lid_index;
-} xfs_log_item_desc_t;
+	ushort			lid_size;
+	unsigned char		lid_flags;
+	struct list_head	lid_trans;
+};
 
 #define XFS_LID_DIRTY		0x1
-#define XFS_LID_PINNED		0x2
-
-/*
- * This structure is used to maintain a chunk list of log_item_desc
- * structures. The free field is a bitmask indicating which descriptors
- * in this chunk's array are free.  The unused field is the first value
- * not used since this chunk was allocated.
- */
-#define	XFS_LIC_NUM_SLOTS	15
-typedef struct xfs_log_item_chunk {
-	struct xfs_log_item_chunk	*lic_next;
-	ushort				lic_free;
-	ushort				lic_unused;
-	xfs_log_item_desc_t		lic_descs[XFS_LIC_NUM_SLOTS];
-} xfs_log_item_chunk_t;
-
-#define	XFS_LIC_MAX_SLOT	(XFS_LIC_NUM_SLOTS - 1)
-#define	XFS_LIC_FREEMASK	((1 << XFS_LIC_NUM_SLOTS) - 1)
-
-
-/*
- * Initialize the given chunk.  Set the chunk's free descriptor mask
- * to indicate that all descriptors are free.  The caller gets to set
- * lic_unused to the right value (0 matches all free).  The
- * lic_descs.lid_index values are set up as each desc is allocated.
- */
-static inline void xfs_lic_init(xfs_log_item_chunk_t *cp)
-{
-	cp->lic_free = XFS_LIC_FREEMASK;
-}
-
-static inline void xfs_lic_init_slot(xfs_log_item_chunk_t *cp, int slot)
-{
-	cp->lic_descs[slot].lid_index = (unsigned char)(slot);
-}
-
-static inline int xfs_lic_vacancy(xfs_log_item_chunk_t *cp)
-{
-	return cp->lic_free & XFS_LIC_FREEMASK;
-}
-
-static inline void xfs_lic_all_free(xfs_log_item_chunk_t *cp)
-{
-	cp->lic_free = XFS_LIC_FREEMASK;
-}
-
-static inline int xfs_lic_are_all_free(xfs_log_item_chunk_t *cp)
-{
-	return ((cp->lic_free & XFS_LIC_FREEMASK) == XFS_LIC_FREEMASK);
-}
-
-static inline int xfs_lic_isfree(xfs_log_item_chunk_t *cp, int slot)
-{
-	return (cp->lic_free & (1 << slot));
-}
-
-static inline void xfs_lic_claim(xfs_log_item_chunk_t *cp, int slot)
-{
-	cp->lic_free &= ~(1 << slot);
-}
-
-static inline void xfs_lic_relse(xfs_log_item_chunk_t *cp, int slot)
-{
-	cp->lic_free |= 1 << slot;
-}
-
-static inline xfs_log_item_desc_t *
-xfs_lic_slot(xfs_log_item_chunk_t *cp, int slot)
-{
-	return &(cp->lic_descs[slot]);
-}
-
-static inline int xfs_lic_desc_to_slot(xfs_log_item_desc_t *dp)
-{
-	return (uint)dp->lid_index;
-}
-
-/*
- * Calculate the address of a chunk given a descriptor pointer:
- * dp - dp->lid_index give the address of the start of the lic_descs array.
- * From this we subtract the offset of the lic_descs field in a chunk.
- * All of this yields the address of the chunk, which is
- * cast to a chunk pointer.
- */
-static inline xfs_log_item_chunk_t *
-xfs_lic_desc_to_chunk(xfs_log_item_desc_t *dp)
-{
-	return (xfs_log_item_chunk_t*) \
-		(((xfs_caddr_t)((dp) - (dp)->lid_index)) - \
-		(xfs_caddr_t)(((xfs_log_item_chunk_t*)0)->lic_descs));
-}
 
 #define	XFS_TRANS_MAGIC		0x5452414E	/* 'TRAN' */
 /*
@@ -516,8 +425,7 @@ typedef struct xfs_trans {
 	int64_t			t_rblocks_delta;/* superblock rblocks change */
 	int64_t			t_rextents_delta;/* superblocks rextents chg */
 	int64_t			t_rextslog_delta;/* superblocks rextslog chg */
-	unsigned int		t_items_free;	/* log item descs free */
-	xfs_log_item_chunk_t	t_items;	/* first log item desc chunk */
+	struct list_head	t_items;	/* log item descriptors */
 	xfs_trans_header_t	t_header;	/* header for in-log trans */
 	struct list_head	t_busy;		/* list of busy extents */
 	unsigned long		t_pflags;	/* saved process flags state */
@@ -595,6 +503,7 @@ int		xfs_trans_ail_init(struct xfs_mount *);
 void		xfs_trans_ail_destroy(struct xfs_mount *);
 
 extern kmem_zone_t	*xfs_trans_zone;
+extern kmem_zone_t	*xfs_log_item_desc_zone;
 
 #endif	/* __KERNEL__ */