[PATCH 3/4] xfs: make xfs_inode_set_eofblocks_tag cheaper for the common case

[Christoph Hellwig <hch@xxxxxx>]

For long growing file writes we will usually already have the eofblocks
tag set when adding more speculative preallocations.  Add a flag in the
inode to allow us to skip the the fairly expensive AG-wide spinlocks
and multiple radix tree operations in that case.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/xfs/xfs_icache.c | 14 ++++++++++++++
 fs/xfs/xfs_inode.h  |  1 +
 2 files changed, 15 insertions(+)

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index fb39a66..65b2e3f 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -1414,6 +1414,16 @@ xfs_inode_set_eofblocks_tag(
        struct xfs_perag *pag;
        int tagged;
 
+       /*
+        * Don't bother locking the AG and looking up in the radix trees
+        * if we already know that we have the tag set.
+        */
+       if (ip->i_flags & XFS_IEOFBLOCKS)
+               return;
+       spin_lock(&ip->i_flags_lock);
+       ip->i_flags |= XFS_IEOFBLOCKS;
+       spin_unlock(&ip->i_flags_lock);
+
        pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
        spin_lock(&pag->pag_ici_lock);
        trace_xfs_inode_set_eofblocks_tag(ip);
@@ -1449,6 +1459,10 @@ xfs_inode_clear_eofblocks_tag(
        struct xfs_mount *mp = ip->i_mount;
        struct xfs_perag *pag;
 
+       spin_lock(&ip->i_flags_lock);
+       ip->i_flags &= ~XFS_IEOFBLOCKS;
+       spin_unlock(&ip->i_flags_lock);
+
        pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
        spin_lock(&pag->pag_ici_lock);
        trace_xfs_inode_clear_eofblocks_tag(ip);
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index e1a411e..8f30d25 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -216,6 +216,7 @@ xfs_get_initial_prid(struct xfs_inode *dp)
 #define __XFS_IPINNED_BIT      8        /* wakeup key for zero pin count */
 #define XFS_IPINNED            (1 << __XFS_IPINNED_BIT)
 #define XFS_IDONTCACHE         (1 << 9) /* don't cache the inode long term */
+#define XFS_IEOFBLOCKS         (1 << 10)/* has the preallocblocks tag set */
 
 /*
  * Per-lifetime flags need to be reset when re-using a reclaimable inode during
-- 
2.1.4