[PATCH v5 2/3] xfs: Set realtime flag based on initial allocation size

[Richard Wareing <rwareing@fb.com>]

- The rt_alloc_min sysfs option automatically selects the device (data
  device, or realtime) based on the size of the initial allocation of the
  file.
- This option can be used to route the storage of small files (and the
  inefficient workloads associated with them) to a suitable storage
  device such a SSD, while larger allocations are sent to a traditional
  HDD.
- Supports writes via O_DIRECT, buffered (i.e. page cache), and
  pre-allocations (i.e. fallocate)
- Available only when kernel is compiled w/ CONFIG_XFS_RT option.

Signed-off-by: Richard Wareing <rwareing@fb.com>
---
Changes since v4:
* Added xfs_inode_select_target function to hold target selection
  code
* XFS_IS_REALTIME_MOUNT check now moved inside xfs_inode_select_target
  function for better gating
* Improved consistency in the sysfs set behavior
* Style fixes

Changes since v3:
* Now functions via initial allocation regardless of O_DIRECT, buffered or
  pre-allocation code paths.  Provides a consistent user-experience.
* I Did do some experiments putting this in the xfs_bmapi_write code path
  however pre-allocation accounting unfortunately prevents this cleaner
  approach.  As such, this proved to be the cleanest and functional approach.
* No longer a mount option, now a sysfs tunable

 fs/xfs/xfs_bmap_util.c |  2 ++
 fs/xfs/xfs_inode.c     | 18 ++++++++++++------
 fs/xfs/xfs_iomap.c     |  5 +++++
 fs/xfs/xfs_mount.h     |  1 +
 fs/xfs/xfs_rtalloc.c   | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/xfs_rtalloc.h   |  2 ++
 fs/xfs/xfs_sysfs.c     | 38 ++++++++++++++++++++++++++++++++++++++
 7 files changed, 110 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 9e3cc21..8205669d 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1026,6 +1026,8 @@ xfs_alloc_file_space(
 	if (len <= 0)
 		return -EINVAL;
 
+	xfs_inode_select_target(ip, len);
+
 	rt = XFS_IS_REALTIME_INODE(ip);
 	extsz = xfs_get_extsz_hint(ip);
 
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index ec9826c..f9e2deb 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1620,12 +1620,18 @@ xfs_itruncate_extents(
 	if (error)
 		goto out;
 
-	/*
-	 * Clear the reflink flag if we truncated everything.
-	 */
-	if (ip->i_d.di_nblocks == 0 && xfs_is_reflink_inode(ip)) {
-		ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
-		xfs_inode_clear_cowblocks_tag(ip);
+	if (ip->i_d.di_nblocks == 0) {
+		/*
+		 * Clear the reflink flag if we truncated everything.
+		 */
+		if (xfs_is_reflink_inode(ip)) {
+			ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
+			xfs_inode_clear_cowblocks_tag(ip);
+		}
+		/* Clear realtime flag if m_rt_alloc_min policy is in place */
+		if (XFS_IS_REALTIME_MOUNT(mp) && mp->m_rt_alloc_min) {
+			ip->i_d.di_flags &= ~XFS_DIFLAG_REALTIME;
+		}
 	}
 
 	/*
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 94e5bdf..b3c3b9b 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -40,6 +40,7 @@
 #include "xfs_dquot_item.h"
 #include "xfs_dquot.h"
 #include "xfs_reflink.h"
+#include "xfs_rtalloc.h"
 
 
 #define XFS_WRITEIO_ALIGN(mp,off)	(((off) >> mp->m_writeio_log) \
@@ -174,6 +175,8 @@ xfs_iomap_write_direct(
 	int		bmapi_flags = XFS_BMAPI_PREALLOC;
 	uint		tflags = 0;
 
+	xfs_inode_select_target(ip, count);
+
 	rt = XFS_IS_REALTIME_INODE(ip);
 	extsz = xfs_get_extsz_hint(ip);
 	lockmode = XFS_ILOCK_SHARED;	/* locked by caller */
@@ -981,6 +984,8 @@ xfs_file_iomap_begin(
 	if (XFS_FORCED_SHUTDOWN(mp))
 		return -EIO;
 
+	xfs_inode_select_target(ip, length);
+
 	if (((flags & (IOMAP_WRITE | IOMAP_DIRECT)) == IOMAP_WRITE) &&
 			!IS_DAX(inode) && !xfs_get_extsz_hint(ip)) {
 		/* Reserve delalloc blocks for regular writeback. */
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 9fa312a..2adc701 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -197,6 +197,7 @@ typedef struct xfs_mount {
 	__uint32_t		m_generation;
 
 	bool			m_fail_unmount;
+	uint			m_rt_alloc_min; /* Min RT allocation */
 #ifdef DEBUG
 	/*
 	 * DEBUG mode instrumentation to test and/or trigger delayed allocation
diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index c57aa7f..421f860 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -1284,3 +1284,53 @@ xfs_rtpick_extent(
 	*pick = b;
 	return 0;
 }
+
+/*
+ * If allocation length is less than rt_alloc_min threshold select the
+ * data device.   Otherwise, select the realtime device.
+ */
+void xfs_rt_alloc_min(
+	struct xfs_mount	*mp,
+	struct xfs_inode	*ip,
+	xfs_off_t			len)
+{
+	if (!mp->m_rt_alloc_min)
+		return;
+
+	if (len < mp->m_rt_alloc_min) {
+		ip->i_d.di_flags &= ~XFS_DIFLAG_REALTIME;
+	} else {
+		ip->i_d.di_flags |= XFS_DIFLAG_REALTIME;
+	}
+}
+
+/*
+* Select the target device for the inode based on either the size of the
+* initial allocation, or the amount of space available on the data device.
+*
+*/
+void xfs_inode_select_target(
+	struct xfs_inode	*ip,
+	xfs_off_t			len)
+{
+	struct xfs_mount    *mp = ip->i_mount;
+
+	/* If the mount does not have a realtime device configured, there's
+	 * nothing to do here.
+	 */
+	if (!XFS_IS_REALTIME_MOUNT(mp))
+		return;
+
+	/* You cannot select a new device target once blocks have been allocated
+	 * (e.g. fallocate() beyond EOF), or if data has been written already.
+	 */
+	if (ip->i_d.di_nextents)
+		return;
+	if (ip->i_d.di_size)
+		return;
+
+	/* m_rt_alloc_min controls target selection.  Target selection code is
+	 * not valid if not set.
+	 */
+	xfs_rt_alloc_min(mp, ip, len);
+}
diff --git a/fs/xfs/xfs_rtalloc.h b/fs/xfs/xfs_rtalloc.h
index f13133e..eaf7ed3 100644
--- a/fs/xfs/xfs_rtalloc.h
+++ b/fs/xfs/xfs_rtalloc.h
@@ -136,6 +136,7 @@ int xfs_rtalloc_query_range(struct xfs_trans *tp,
 int xfs_rtalloc_query_all(struct xfs_trans *tp,
 			  xfs_rtalloc_query_range_fn fn,
 			  void *priv);
+void xfs_inode_select_target(struct xfs_inode *ip, xfs_off_t len);
 #else
 # define xfs_rtallocate_extent(t,b,min,max,l,f,p,rb)    (ENOSYS)
 # define xfs_rtfree_extent(t,b,l)                       (ENOSYS)
@@ -155,6 +156,7 @@ xfs_rtmount_init(
 }
 # define xfs_rtmount_inodes(m)  (((mp)->m_sb.sb_rblocks == 0)? 0 : (ENOSYS))
 # define xfs_rtunmount_inodes(m)
+# define xfs_inode_select_target(i,l)
 #endif	/* CONFIG_XFS_RT */
 
 #endif	/* __XFS_RTALLOC_H__ */
diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
index 80ac15f..1e202a1 100644
--- a/fs/xfs/xfs_sysfs.c
+++ b/fs/xfs/xfs_sysfs.c
@@ -129,10 +129,48 @@ XFS_SYSFS_ATTR_RW(drop_writes);
 
 #endif /* DEBUG */
 
+STATIC ssize_t
+rt_alloc_min_store(
+	struct kobject			*kobject,
+	const char				*buf,
+	size_t					count)
+{
+	struct xfs_mount		*mp = to_mp(kobject);
+	int						ret;
+	int						val;
+
+	ret = kstrtoint(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	/* Only valid if using a real-time device */
+	if(!XFS_IS_REALTIME_MOUNT(mp))
+		return -EINVAL;
+
+	if (val >= 0)
+		mp->m_rt_alloc_min = val;
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+STATIC ssize_t
+rt_alloc_min_show(
+	struct kobject          *kobject,
+	char                    *buf)
+{
+	struct xfs_mount        *mp = to_mp(kobject);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", mp->m_rt_alloc_min);
+}
+XFS_SYSFS_ATTR_RW(rt_alloc_min);
+
 static struct attribute *xfs_mp_attrs[] = {
 #ifdef DEBUG
 	ATTR_LIST(drop_writes),
 #endif
+	ATTR_LIST(rt_alloc_min),
 	NULL,
 };
 
-- 
2.9.5