xfs: replace dop_low with transaction flag

The dop_low field enables the low free space allocation mode when a
previous allocation has detected difficulty allocating blocks. It
has historically been part of the xfs_defer_ops structure, which
means if enabled, it remains enabled across a set of transactions
until the deferred operations have completed and the dfops is reset.

Now that the dfops is embedded in the transaction, we can save a bit
more space by using a transaction flag rather than a standalone
boolean. Drop the ->dop_low field and replace it with a transaction
flag that is set at the same points, carried across rolling
transactions and cleared on completion of deferred operations. This
essentially emulates the behavior of ->dop_low and so should not
change behavior.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

8 files changed, 36 insertions, 30 deletions

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index a85c0445b38f..8edf7522aaff 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -700,7 +700,7 @@ xfs_bmap_extents_to_btree(
         if (tp->t_firstblock == NULLFSBLOCK) {
                 args.type = XFS_ALLOCTYPE_START_BNO;
                 args.fsbno = XFS_INO_TO_FSB(mp, ip->i_ino);
-        } else if (tp->t_dfops->dop_low) {
+        } else if (tp->t_flags & XFS_TRANS_LOWMODE) {
                 args.type = XFS_ALLOCTYPE_START_BNO;
                 args.fsbno = tp->t_firstblock;
         } else {
@@ -3449,7 +3449,7 @@ xfs_bmap_btalloc(
                         error = xfs_bmap_btalloc_nullfb(ap, &args, &blen);
                 if (error)
                         return error;
-        } else if (ap->tp->t_dfops->dop_low) {
+        } else if (ap->tp->t_flags & XFS_TRANS_LOWMODE) {
                 if (xfs_inode_is_filestream(ap->ip))
                         args.type = XFS_ALLOCTYPE_FIRST_AG;
                 else
@@ -3484,7 +3484,7 @@ xfs_bmap_btalloc(
          * is >= the stripe unit and the allocation offset is
          * at the end of file.
          */
-        if (!ap->tp->t_dfops->dop_low && ap->aeof) {
+        if (!(ap->tp->t_flags & XFS_TRANS_LOWMODE) && ap->aeof) {
                 if (!ap->offset) {
                         args.alignment = stripe_align;
                         atype = args.type;
@@ -3576,7 +3576,7 @@ xfs_bmap_btalloc(
                 args.total = ap->minlen;
                 if ((error = xfs_alloc_vextent(&args)))
                         return error;
-                ap->tp->t_dfops->dop_low = true;
+                ap->tp->t_flags |= XFS_TRANS_LOWMODE;
         }
         if (args.fsbno != NULLFSBLOCK) {
                 /*
diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
index 01489714a253..955e29de8cae 100644
--- a/fs/xfs/libxfs/xfs_bmap_btree.c
+++ b/fs/xfs/libxfs/xfs_bmap_btree.c
@@ -226,7 +226,7 @@ xfs_bmbt_alloc_block(
                  * block allocation here and corrupt the filesystem.
                  */
                 args.minleft = args.tp->t_blk_res;
-        } else if (cur->bc_tp->t_dfops->dop_low) {
+        } else if (cur->bc_tp->t_flags & XFS_TRANS_LOWMODE) {
                 args.type = XFS_ALLOCTYPE_START_BNO;
         } else {
                 args.type = XFS_ALLOCTYPE_NEAR_BNO;
@@ -253,7 +253,7 @@ xfs_bmbt_alloc_block(
                 error = xfs_alloc_vextent(&args);
                 if (error)
                         goto error0;
-                cur->bc_tp->t_dfops->dop_low = true;
+                cur->bc_tp->t_flags |= XFS_TRANS_LOWMODE;
         }
         if (WARN_ON_ONCE(args.fsbno == NULLFSBLOCK)) {
                 *stat = 0;
diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
index e3517a53c525..64e1abc60edc 100644
--- a/fs/xfs/libxfs/xfs_defer.c
+++ b/fs/xfs/libxfs/xfs_defer.c
@@ -330,9 +330,14 @@ xfs_defer_reset(
 
         ASSERT(!xfs_defer_has_unfinished_work(dop));
 
-        dop->dop_low = false;
         memset(dop->dop_inodes, 0, sizeof(dop->dop_inodes));
         memset(dop->dop_bufs, 0, sizeof(dop->dop_bufs));
+
+        /*
+         * Low mode state transfers across transaction rolls to mirror dfops
+         * lifetime. Clear it now that dfops is reset.
+         */
+        tp->t_flags &= ~XFS_TRANS_LOWMODE;
 }
 
 /*
@@ -590,7 +595,14 @@ xfs_defer_move(
 
         memcpy(dst->dop_inodes, src->dop_inodes, sizeof(dst->dop_inodes));
         memcpy(dst->dop_bufs, src->dop_bufs, sizeof(dst->dop_bufs));
-        dst->dop_low = src->dop_low;
+
+        /*
+         * Low free space mode was historically controlled by a dfops field.
+         * This meant that low mode state potentially carried across multiple
+         * transaction rolls. Transfer low mode on a dfops move to preserve
+         * that behavior.
+         */
+        dtp->t_flags |= (stp->t_flags & XFS_TRANS_LOWMODE);
 
         xfs_defer_reset(stp);
 }
diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
index d60c50498fdf..8908a2716774 100644
--- a/fs/xfs/libxfs/xfs_defer.h
+++ b/fs/xfs/libxfs/xfs_defer.h
@@ -25,17 +25,6 @@ struct xfs_defer_pending {
 
 /*
  * Header for deferred operation list.
- *
- * dop_low is used by the allocator to activate the lowspace algorithm -
- * when free space is running low the extent allocator may choose to
- * allocate an extent from an AG without leaving sufficient space for
- * a btree split when inserting the new extent.  In this case the allocator
- * will enable the lowspace algorithm which is supposed to allow further
- * allocations (such as btree splits and newroots) to allocate from
- * sequential AGs.  In order to avoid locking AGs out of order the lowspace
- * algorithm will start searching for free space from AG 0.  If the correct
- * transaction reservations have been made then this algorithm will eventually
- * find all the space it needs.
  */
 enum xfs_defer_ops_type {
         XFS_DEFER_OPS_TYPE_BMAP,
diff --git a/fs/xfs/libxfs/xfs_shared.h b/fs/xfs/libxfs/xfs_shared.h
index 22089f1c880a..1c5debe748f0 100644
--- a/fs/xfs/libxfs/xfs_shared.h
+++ b/fs/xfs/libxfs/xfs_shared.h
@@ -64,6 +64,18 @@ void	xfs_log_get_max_trans_res(struct xfs_mount *mp,
 #define XFS_TRANS_RESERVE       0x20    /* OK to use reserved data blocks */
 #define XFS_TRANS_NO_WRITECOUNT 0x40    /* do not elevate SB writecount */
 #define XFS_TRANS_NOFS          0x80    /* pass KM_NOFS to kmem_alloc */
+/*
+ * LOWMODE is used by the allocator to activate the lowspace algorithm - when
+ * free space is running low the extent allocator may choose to allocate an
+ * extent from an AG without leaving sufficient space for a btree split when
+ * inserting the new extent. In this case the allocator will enable the
+ * lowspace algorithm which is supposed to allow further allocations (such as
+ * btree splits and newroots) to allocate from sequential AGs. In order to
+ * avoid locking AGs out of order the lowspace algorithm will start searching
+ * for free space from AG 0. If the correct transaction reservations have been
+ * made then this algorithm will eventually find all the space it needs.
+ */
+#define XFS_TRANS_LOWMODE       0x100   /* allocate in low space mode */
 
 /*
  * Field values for xfs_trans_mod_sb.
diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
index 212173c62588..182501373af2 100644
--- a/fs/xfs/xfs_filestream.c
+++ b/fs/xfs/xfs_filestream.c
@@ -20,6 +20,7 @@
 #include "xfs_trace.h"
 #include "xfs_ag_resv.h"
 #include "xfs_trans.h"
+#include "xfs_shared.h"
 
 struct xfs_fstrm_item {
         struct xfs_mru_cache_elem       mru;
@@ -378,7 +379,7 @@ xfs_filestream_new_ag(
 
         if (xfs_alloc_is_userdata(ap->datatype))
                 flags |= XFS_PICK_USERDATA;
-        if (ap->tp->t_dfops->dop_low)
+        if (ap->tp->t_flags & XFS_TRANS_LOWMODE)
                 flags |= XFS_PICK_LOWSPACE;
 
         err = xfs_filestream_pick_ag(pip, startag, agp, flags, minlen);
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index cc6995cfce66..8807f1bb814a 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -2223,19 +2223,16 @@ DECLARE_EVENT_CLASS(xfs_defer_class,
                 __field(dev_t, dev)
                 __field(void *, dop)
                 __field(char, committed)
-                __field(char, low)
                 __field(unsigned long, caller_ip)
         ),
         TP_fast_assign(
                 __entry->dev = mp ? mp->m_super->s_dev : 0;
                 __entry->dop = dop;
-                __entry->low = dop->dop_low;
                 __entry->caller_ip = caller_ip;
         ),
-        TP_printk("dev %d:%d ops %p low %d, caller %pS",
+        TP_printk("dev %d:%d ops %p caller %pS",
                   MAJOR(__entry->dev), MINOR(__entry->dev),
                   __entry->dop,
-                  __entry->low,
                   (char *)__entry->caller_ip)
 )
 #define DEFINE_DEFER_EVENT(name) \
@@ -2251,19 +2248,16 @@ DECLARE_EVENT_CLASS(xfs_defer_error_class,
                 __field(dev_t, dev)
                 __field(void *, dop)
                 __field(char, committed)
-                __field(char, low)
                 __field(int, error)
         ),
         TP_fast_assign(
                 __entry->dev = mp ? mp->m_super->s_dev : 0;
                 __entry->dop = dop;
-                __entry->low = dop->dop_low;
                 __entry->error = error;
         ),
-        TP_printk("dev %d:%d ops %p low %d err %d",
+        TP_printk("dev %d:%d ops %p err %d",
                   MAJOR(__entry->dev), MINOR(__entry->dev),
                   __entry->dop,
-                  __entry->low,
                   __entry->error)
 )
 #define DEFINE_DEFER_ERROR_EVENT(name) \
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index dc79e3c1d3e8..7e493221160e 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -101,8 +101,6 @@ struct xfs_defer_ops {
         /* relog these with each roll */
         struct xfs_inode        *dop_inodes[XFS_DEFER_OPS_NR_INODES];
         struct xfs_buf          *dop_bufs[XFS_DEFER_OPS_NR_BUFS];
-
-        bool                    dop_low;        /* alloc in low mode */
 };
 
 /*