[PATCH v2 2/3] xfs: xfs_defer_capture should absorb remaining block reservation

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

When xfs_defer_capture extracts the deferred ops and transaction state
from a transaction, it should absorb the remaining block reservation so
that when we continue the dfops chain, we still have those blocks to
use.

This adds the requirement that every log intent item recovery function
must be careful to reserve enough blocks to handle both itself and all
defer ops that it can queue.  On the other hand, this enables us to do
away with the handwaving block estimation nonsense that was going on in
xlog_finish_defer_ops.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
v2: trivial rebase of patch 1
---
 fs/xfs/libxfs/xfs_defer.c |    4 ++++
 fs/xfs/libxfs/xfs_defer.h |    1 +
 fs/xfs/xfs_log_recover.c  |   18 +-----------------
 3 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
index 0cb4af0c5c10..8bd01952c955 100644
--- a/fs/xfs/libxfs/xfs_defer.c
+++ b/fs/xfs/libxfs/xfs_defer.c
@@ -593,6 +593,8 @@ xfs_defer_capture(
 	/* Move the dfops chain and transaction state to the freezer. */
 	list_splice_init(&tp->t_dfops, &dfc->dfc_dfops);
 	dfc->dfc_tpflags = tp->t_flags & XFS_TRANS_LOWMODE;
+	dfc->dfc_blkres = tp->t_blk_res - tp->t_blk_res_used;
+	tp->t_blk_res = tp->t_blk_res_used;
 	xfs_defer_reset(tp);
 
 	/*
@@ -622,6 +624,8 @@ xfs_defer_continue(
 	list_splice_init(&dfc->dfc_dfops, &tp->t_dfops);
 	tp->t_flags |= dfc->dfc_tpflags;
 	dfc->dfc_tpflags = 0;
+	tp->t_blk_res += dfc->dfc_blkres;
+	dfc->dfc_blkres = 0;
 }
 
 /* Release all resources that we used to capture deferred ops. */
diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
index 366d08d99e11..59d126aeb31c 100644
--- a/fs/xfs/libxfs/xfs_defer.h
+++ b/fs/xfs/libxfs/xfs_defer.h
@@ -76,6 +76,7 @@ struct xfs_defer_capture {
 	/* Deferred ops state saved from the transaction. */
 	struct list_head	dfc_dfops;
 	unsigned int		dfc_tpflags;
+	unsigned int		dfc_blkres;
 };
 
 /*
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 79be1f02d1b4..777b60073ff7 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -2501,26 +2501,10 @@ xlog_finish_defer_ops(
 {
 	struct xfs_defer_capture *dfc, *next;
 	struct xfs_trans	*tp;
-	int64_t			freeblks;
-	uint64_t		resblks;
 	int			error = 0;
 
 	list_for_each_entry_safe(dfc, next, capture_list, dfc_list) {
-		/*
-		 * We're finishing the defer_ops that accumulated as a result
-		 * of recovering unfinished intent items during log recovery.
-		 * We reserve an itruncate transaction because it is the
-		 * largest permanent transaction type.  Since we're the only
-		 * user of the fs right now, take 93% (15/16) of the available
-		 * free blocks.  Use weird math to avoid a 64-bit division.
-		 */
-		freeblks = percpu_counter_sum(&mp->m_fdblocks);
-		if (freeblks <= 0)
-			return -ENOSPC;
-
-		resblks = min_t(uint64_t, UINT_MAX, freeblks);
-		resblks = (resblks * 15) >> 4;
-		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, resblks,
+		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0,
 				0, XFS_TRANS_RESERVE, &tp);
 		if (error)
 			return error;