[PATCH 099/119] xfs: don't allow reflink when the AG is low on space

Darrick J. Wong
2016-06-17T01:28:41Z

If the AG free space is down to the reserves, refuse to reflink our
way out of space. Hopefully userspace will make a real copy and/or go
elsewhere.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/xfs/xfs_reflink.c | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index d2c1547..f5195b7 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -53,6 +53,8 @@
#include "xfs_reflink.h"
#include "xfs_iomap.h"
#include "xfs_rmap_btree.h"
+#include "xfs_sb.h"
+#include "xfs_ag_resv.h"

/*
* Copy on Write of Shared Blocks
@@ -1056,6 +1058,30 @@ out_error:
}

/*
+ * Do we have enough reserve in this AG to handle a reflink? The refcount
+ * btree already reserved all the space it needs, but the rmap btree can grow
+ * infinitely, so we won't allow more reflinks when the AG is down to the
+ * btree reserves.
+ */
+static int
+xfs_reflink_ag_has_free_space(
+ struct xfs_mount *mp,
+ xfs_agnumber_t agno)
+{
+ struct xfs_perag *pag;
+ int error = 0;
+
+ if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
+ return 0;
+
+ pag = xfs_perag_get(mp, agno);
+ if (xfs_ag_resv_critical(pag, XFS_AG_RESV_AGFL))
+ error = -ENOSPC;
+ xfs_perag_put(pag);
+ return error;
+}
+
+/*
* Unmap a range of blocks from a file, then map other blocks into the hole.
* The range to unmap is (destoff : destoff + srcioff + irec->br_blockcount).
* The extent irec is mapped into dest at irec->br_startoff.
@@ -1087,6 +1113,14 @@ xfs_reflink_remap_extent(
irec->br_startblock != DELAYSTARTBLOCK &&
!ISUNWRITTEN(irec));

+ /* No reflinking if we're low on space */
+ if (real_extent) {
+ error = xfs_reflink_ag_has_free_space(mp,
+ XFS_FSB_TO_AGNO(mp, irec->br_startblock));
+ if (error)
+ goto out;
+ }
+
/* Start a rolling transaction to switch the mappings */
resblks = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);