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, 15 insertions, 49 deletions

diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
index d1d08aa404b5..74a1c33e4098 100644
--- a/fs/xfs/xfs_trans_buf.c
+++ b/fs/xfs/xfs_trans_buf.c
@@ -47,36 +47,17 @@ xfs_trans_buf_item_match(
         xfs_daddr_t             blkno,
         int                     len)
 {
-        xfs_log_item_chunk_t    *licp;
-        xfs_log_item_desc_t     *lidp;
-        xfs_buf_log_item_t      *blip;
-        int                     i;
+        struct xfs_log_item_desc *lidp;
+        struct xfs_buf_log_item *blip;
 
         len = BBTOB(len);
-        for (licp = &tp->t_items; licp != NULL; licp = licp->lic_next) {
-                if (xfs_lic_are_all_free(licp)) {
-                        ASSERT(licp == &tp->t_items);
-                        ASSERT(licp->lic_next == NULL);
-                        return NULL;
-                }
-
-                for (i = 0; i < licp->lic_unused; i++) {
-                        /*
-                         * Skip unoccupied slots.
-                         */
-                        if (xfs_lic_isfree(licp, i))
-                                continue;
-
-                        lidp = xfs_lic_slot(licp, i);
-                        blip = (xfs_buf_log_item_t *)lidp->lid_item;
-                        if (blip->bli_item.li_type != XFS_LI_BUF)
-                                continue;
-
-                        if (XFS_BUF_TARGET(blip->bli_buf) == target &&
-                            XFS_BUF_ADDR(blip->bli_buf) == blkno &&
-                            XFS_BUF_COUNT(blip->bli_buf) == len)
-                                return blip->bli_buf;
-                }
+        list_for_each_entry(lidp, &tp->t_items, lid_trans) {
+                blip = (struct xfs_buf_log_item *)lidp->lid_item;
+                if (blip->bli_item.li_type == XFS_LI_BUF &&
+                    XFS_BUF_TARGET(blip->bli_buf) == target &&
+                    XFS_BUF_ADDR(blip->bli_buf) == blkno &&
+                    XFS_BUF_COUNT(blip->bli_buf) == len)
+                        return blip->bli_buf;
         }
 
         return NULL;
@@ -123,7 +104,7 @@ _xfs_trans_bjoin(
         /*
          * Get a log_item_desc to point at the new item.
          */
-        (void) xfs_trans_add_item(tp, (xfs_log_item_t *)bip);
+        xfs_trans_add_item(tp, &bip->bli_item);
 
         /*
          * Initialize b_fsprivate2 so we can find it with incore_match()
@@ -479,7 +460,6 @@ xfs_trans_brelse(xfs_trans_t	*tp,
 {
         xfs_buf_log_item_t      *bip;
         xfs_log_item_t          *lip;
-        xfs_log_item_desc_t     *lidp;
 
         /*
          * Default to a normal brelse() call if the tp is NULL.
@@ -510,13 +490,6 @@ xfs_trans_brelse(xfs_trans_t	*tp,
         ASSERT(!(bip->bli_format.blf_flags & XFS_BLF_CANCEL));
         ASSERT(atomic_read(&bip->bli_refcount) > 0);
 
-        /*
-         * Find the item descriptor pointing to this buffer's
-         * log item.  It must be there.
-         */
-        lidp = xfs_trans_find_item(tp, (xfs_log_item_t*)bip);
-        ASSERT(lidp != NULL);
-
         trace_xfs_trans_brelse(bip);
 
         /*
@@ -532,7 +505,7 @@ xfs_trans_brelse(xfs_trans_t	*tp,
          * If the buffer is dirty within this transaction, we can't
          * release it until we commit.
          */
-        if (lidp->lid_flags & XFS_LID_DIRTY)
+        if (bip->bli_item.li_desc->lid_flags & XFS_LID_DIRTY)
                 return;
 
         /*
@@ -549,7 +522,7 @@ xfs_trans_brelse(xfs_trans_t	*tp,
         /*
          * Free up the log item descriptor tracking the released item.
          */
-        xfs_trans_free_item(tp, lidp);
+        xfs_trans_del_item(&bip->bli_item);
 
         /*
          * Clear the hold flag in the buf log item if it is set.
@@ -661,7 +634,6 @@ xfs_trans_log_buf(xfs_trans_t	*tp,
                   uint          last)
 {
         xfs_buf_log_item_t      *bip;
-        xfs_log_item_desc_t     *lidp;
 
         ASSERT(XFS_BUF_ISBUSY(bp));
         ASSERT(XFS_BUF_FSPRIVATE2(bp, xfs_trans_t *) == tp);
@@ -703,11 +675,8 @@ xfs_trans_log_buf(xfs_trans_t	*tp,
                 bip->bli_format.blf_flags &= ~XFS_BLF_CANCEL;
         }
 
-        lidp = xfs_trans_find_item(tp, (xfs_log_item_t*)bip);
-        ASSERT(lidp != NULL);
-
         tp->t_flags |= XFS_TRANS_DIRTY;
-        lidp->lid_flags |= XFS_LID_DIRTY;
+        bip->bli_item.li_desc->lid_flags |= XFS_LID_DIRTY;
         bip->bli_flags |= XFS_BLI_LOGGED;
         xfs_buf_item_log(bip, first, last);
 }
@@ -736,7 +705,6 @@ xfs_trans_binval(
         xfs_trans_t     *tp,
         xfs_buf_t       *bp)
 {
-        xfs_log_item_desc_t     *lidp;
         xfs_buf_log_item_t      *bip;
 
         ASSERT(XFS_BUF_ISBUSY(bp));
@@ -744,8 +712,6 @@ xfs_trans_binval(
         ASSERT(XFS_BUF_FSPRIVATE(bp, void *) != NULL);
 
         bip = XFS_BUF_FSPRIVATE(bp, xfs_buf_log_item_t *);
-        lidp = xfs_trans_find_item(tp, (xfs_log_item_t*)bip);
-        ASSERT(lidp != NULL);
         ASSERT(atomic_read(&bip->bli_refcount) > 0);
 
         trace_xfs_trans_binval(bip);
@@ -760,7 +726,7 @@ xfs_trans_binval(
                 ASSERT(!(bip->bli_flags & (XFS_BLI_LOGGED | XFS_BLI_DIRTY)));
                 ASSERT(!(bip->bli_format.blf_flags & XFS_BLF_INODE_BUF));
                 ASSERT(bip->bli_format.blf_flags & XFS_BLF_CANCEL);
-                ASSERT(lidp->lid_flags & XFS_LID_DIRTY);
+                ASSERT(bip->bli_item.li_desc->lid_flags & XFS_LID_DIRTY);
                 ASSERT(tp->t_flags & XFS_TRANS_DIRTY);
                 return;
         }
@@ -793,7 +759,7 @@ xfs_trans_binval(
         bip->bli_format.blf_flags |= XFS_BLF_CANCEL;
         memset((char *)(bip->bli_format.blf_data_map), 0,
               (bip->bli_format.blf_map_size * sizeof(uint)));
-        lidp->lid_flags |= XFS_LID_DIRTY;
+        bip->bli_item.li_desc->lid_flags |= XFS_LID_DIRTY;
         tp->t_flags |= XFS_TRANS_DIRTY;
 }