[PATCH 08/10] xfs: introduce a XFS_BMAPI_BESTEFFORT flag

From: Christoph Hellwig <hch@lst.de>
To: linux-xfs@vger.kernel.org
Subject: [PATCH 08/10] xfs: introduce a XFS_BMAPI_BESTEFFORT flag
Date: Thu, 13 Apr 2017 10:05:15 +0200	[thread overview]
Message-ID: <20170413080517.12564-9-hch@lst.de> (raw)
In-Reply-To: <20170413080517.12564-1-hch@lst.de>

We currently have two classes of xfs_bmapi_write callers that have
conflicting space reservation needs.  Many callers expect to be able
to reserve the number of total blocks passed in a single AG for
the use with the current allocation as well as future allocations
in the same transactions, or transactions chained off from it.

Other callers want to allocate up to the number of blocks passed in,
although they are fine with a smaller number of blocks to make
forward progress.  For those we only need to leave a few blocks aside
for the bmap btree manipulations when doing the main space allocation.

This patch introduces a new XFS_BMAPI_BESTEFFORT flag for the second
kind of callers that ignores the total flag and just uses the minleft
parameter to leave space for bmap btree allocations and splits.

With this we can remove the potentially dangerous fallback that
ignores the total reservation in xfs_bmap_btalloc.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/libxfs/xfs_attr_remote.c |  6 ++++--
 fs/xfs/libxfs/xfs_bmap.c        | 27 ++++++++++++++++++++-------
 fs/xfs/libxfs/xfs_bmap.h        |  3 +++
 fs/xfs/xfs_bmap_util.c          |  2 ++
 fs/xfs/xfs_iomap.c              |  4 ++--
 fs/xfs/xfs_reflink.c            |  3 ++-
 6 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
index d52f525f5b2d..35a99d15521c 100644
--- a/fs/xfs/libxfs/xfs_attr_remote.c
+++ b/fs/xfs/libxfs/xfs_attr_remote.c
@@ -464,8 +464,10 @@ xfs_attr_rmtval_set(
 		xfs_defer_init(args->dfops, args->firstblock);
 		nmap = 1;
 		error = xfs_bmapi_write(args->trans, dp, (xfs_fileoff_t)lblkno,
-				  blkcnt, XFS_BMAPI_ATTRFORK, args->firstblock,
-				  args->total, &map, &nmap, args->dfops);
+				  blkcnt,
+				  XFS_BMAPI_ATTRFORK | XFS_BMAPI_BESTEFFORT,
+				  args->firstblock, args->total, &map, &nmap,
+				  args->dfops);
 		if (!error)
 			error = xfs_defer_finish(&args->trans, args->dfops, dp);
 		if (error) {
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 6faefa342748..c06e7d500ed1 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -915,7 +915,7 @@ xfs_bmap_local_to_extents(
 		args.fsbno = *firstblock;
 		args.type = XFS_ALLOCTYPE_NEAR_BNO;
 	}
-	args.total = args.minlen = args.maxlen = args.prod = 1;
+	args.minlen = args.maxlen = args.prod = 1;
 	error = xfs_alloc_vextent(&args);
 	if (error)
 		goto done;
@@ -3504,7 +3504,6 @@ xfs_bmap_btalloc_nullfb(
 	int			error;
 
 	args->type = XFS_ALLOCTYPE_START_BNO;
-	args->total = ap->total;
 
 	startag = ag = XFS_FSB_TO_AGNO(mp, args->fsbno);
 	if (startag == NULLAGNUMBER)
@@ -3538,7 +3537,6 @@ xfs_bmap_btalloc_filestreams(
 	int			error;
 
 	args->type = XFS_ALLOCTYPE_NEAR_BNO;
-	args->total = ap->total;
 
 	ag = XFS_FSB_TO_AGNO(mp, args->fsbno);
 	if (ag == NULLAGNUMBER)
@@ -3684,10 +3682,9 @@ xfs_bmap_btalloc(
 			args.type = XFS_ALLOCTYPE_FIRST_AG;
 		else
 			args.type = XFS_ALLOCTYPE_START_BNO;
-		args.total = args.minlen = 1;
+		args.minlen = 1;
 	} else {
 		args.type = XFS_ALLOCTYPE_NEAR_BNO;
-		args.total = ap->total;
 		args.minlen = 1;
 	}
 	/* apply extent size hints if obtained earlier */
@@ -3754,7 +3751,24 @@ xfs_bmap_btalloc(
 		args.alignment = 1;
 		args.minalignslop = 0;
 	}
-	args.minleft = xfs_bmap_minleft(ap);
+
+	/*
+	 * If the XFS_BMAPI_BESTEFFORT flag is set we try to allocate any
+	 * space that's available, even if it is less than requested.  We
+	 * still need to set a minleft value to guarantee that we can still
+	 * manipulate the bmap btree, though.  The total value is ignored in
+	 * this case.
+	 *
+	 * If the flag is not set the total value specifies the total space
+	 * that the transaction may use, and we must find an AG that has
+	 * enough space available for all of total, or this allocation request
+	 * will fail.
+	 */
+	if (ap->flags & XFS_BMAPI_BESTEFFORT)
+		args.minleft = xfs_bmap_minleft(ap);
+	else
+		args.total = ap->total;
+
 	args.wasdel = ap->wasdel;
 	args.resv = XFS_AG_RESV_NONE;
 	args.datatype = ap->datatype;
@@ -3800,7 +3814,6 @@ xfs_bmap_btalloc(
 	if (args.fsbno == NULLFSBLOCK && nullfb) {
 		args.fsbno = 0;
 		args.type = XFS_ALLOCTYPE_FIRST_AG;
-		args.total = 1;
 		if ((error = xfs_alloc_vextent(&args)))
 			return error;
 		ap->dfops->dop_low = true;
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index 36a7f36f5f38..f35a2b2c4f06 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -79,6 +79,9 @@ struct xfs_extent_free_item
 #define XFS_BMAPI_PREALLOC	0x008	/* preallocation op: unwritten space */
 #define XFS_BMAPI_IGSTATE	0x010	/* Ignore state - */
 					/* combine contig. space */
+
+#define XFS_BMAPI_BESTEFFORT	0x020	/* may allocate less than requested */
+
 /*
  * unwritten extent conversion - this needs write cache flushing and no additional
  * allocation alignments. When specified with XFS_BMAPI_PREALLOC it converts
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 4d1920e594b0..f809ebc7a495 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1033,6 +1033,8 @@ xfs_alloc_file_space(
 	startoffset_fsb	= XFS_B_TO_FSBT(mp, offset);
 	allocatesize_fsb = XFS_B_TO_FSB(mp, count);
 
+	alloc_type |= XFS_BMAPI_BESTEFFORT;
+
 	/*
 	 * Allocate file space until done or until there is an error
 	 */
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 009f8243dddc..1abed9b6d5c5 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -171,7 +171,7 @@ xfs_iomap_write_direct(
 	uint		qblocks, resblks, resrtextents;
 	int		error;
 	int		lockmode;
-	int		bmapi_flags = XFS_BMAPI_PREALLOC;
+	int		bmapi_flags = XFS_BMAPI_PREALLOC | XFS_BMAPI_BESTEFFORT;
 	uint		tflags = 0;
 
 	rt = XFS_IS_REALTIME_INODE(ip);
@@ -679,7 +679,7 @@ xfs_iomap_write_allocate(
 	xfs_trans_t	*tp;
 	int		nimaps;
 	int		error = 0;
-	int		flags = XFS_BMAPI_DELALLOC;
+	int		flags = XFS_BMAPI_DELALLOC | XFS_BMAPI_BESTEFFORT;
 	int		nres;
 
 	if (whichfork == XFS_COW_FORK)
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index c0f3754caca2..aad321c16d2f 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -455,7 +455,8 @@ xfs_reflink_allocate_cow(
 
 	/* Allocate the entire reservation as unwritten blocks. */
 	error = xfs_bmapi_write(tp, ip, imap->br_startoff, imap->br_blockcount,
-			XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC, &first_block,
+			XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC |
+			XFS_BMAPI_BESTEFFORT, &first_block,
 			resblks, imap, &nimaps, &dfops);
 	if (error)
 		goto out_bmap_cancel;
-- 
2.11.0

