[PATCH v3 6/7] xfs: Add RT atomic write unit max to xfs_mount

[John Garry <john.g.garry@oracle.com>]

rtvol guarantees alloc unit alignment through rt_extsize. As such, it is
possible to atomically write multiple FS blocks in a rtvol (up to
rt_extsize).

Add a member to xfs_mount to hold the pre-calculated atomic write unit max.

The value in rt_extsize is not necessarily a power-of-2, so find the
largest power-of-2 evenly divisible into rt_extsize.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 fs/xfs/libxfs/xfs_sb.c |  3 +++
 fs/xfs/xfs_mount.h     |  1 +
 fs/xfs/xfs_rtalloc.c   | 23 +++++++++++++++++++++++
 fs/xfs/xfs_rtalloc.h   |  4 ++++
 4 files changed, 31 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index 3b5623611eba..6381060df901 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -25,6 +25,7 @@
 #include "xfs_da_format.h"
 #include "xfs_health.h"
 #include "xfs_ag.h"
+#include "xfs_rtalloc.h"
 #include "xfs_rtbitmap.h"
 #include "xfs_exchrange.h"
 #include "xfs_rtgroup.h"
@@ -1149,6 +1150,8 @@ xfs_sb_mount_rextsize(
 		rgs->blklog = 0;
 		rgs->blkmask = (uint64_t)-1;
 	}
+
+	xfs_rt_awu_update(mp);
 }
 
 /* Update incore sb rt extent size, then recompute the cached rt geometry. */
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index db9dade7d22a..f2f1d2c667cc 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -191,6 +191,7 @@ typedef struct xfs_mount {
 	bool			m_fail_unmount;
 	bool			m_finobt_nores; /* no per-AG finobt resv. */
 	bool			m_update_sb;	/* sb needs update in mount */
+	xfs_extlen_t		m_rt_awu_max;   /* rt atomic write unit max */
 
 	/*
 	 * Bitsets of per-fs metadata that have been checked and/or are sick.
diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index fcfa6e0eb3ad..e3093f3c7670 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -735,6 +735,28 @@ xfs_rtginode_ensure(
 	return xfs_rtginode_create(rtg, type, true);
 }
 
+void
+xfs_rt_awu_update(
+	struct xfs_mount	*mp)
+{
+	xfs_agblock_t		rsize = mp->m_sb.sb_rextsize;
+	xfs_extlen_t		awu_max;
+
+	if (is_power_of_2(rsize)) {
+		mp->m_rt_awu_max = rsize;
+		return;
+	}
+
+	/* Find highest power-of-2 evenly divisible into sb_rextsize */
+	awu_max = 1;
+	while (1) {
+		if (rsize % (awu_max * 2))
+			break;
+		awu_max *= 2;
+	}
+	mp->m_rt_awu_max = awu_max;
+}
+
 static struct xfs_mount *
 xfs_growfs_rt_alloc_fake_mount(
 	const struct xfs_mount	*mp,
@@ -969,6 +991,7 @@ xfs_growfs_rt_bmblock(
 	 */
 	mp->m_rsumlevels = nmp->m_rsumlevels;
 	mp->m_rsumblocks = nmp->m_rsumblocks;
+	mp->m_rt_awu_max = nmp->m_rt_awu_max;
 
 	/*
 	 * Recompute the growfsrt reservation from the new rsumsize.
diff --git a/fs/xfs/xfs_rtalloc.h b/fs/xfs/xfs_rtalloc.h
index 8e2a07b8174b..fcb7bb3df470 100644
--- a/fs/xfs/xfs_rtalloc.h
+++ b/fs/xfs/xfs_rtalloc.h
@@ -42,6 +42,10 @@ xfs_growfs_rt(
 	struct xfs_mount	*mp,	/* file system mount structure */
 	xfs_growfs_rt_t		*in);	/* user supplied growfs struct */
 
+void
+xfs_rt_awu_update(
+	struct xfs_mount	*mp);
+
 int xfs_rtalloc_reinit_frextents(struct xfs_mount *mp);
 #else
 # define xfs_growfs_rt(mp,in)				(-ENOSYS)
-- 
2.31.1