[XFS] Concurrent Multi-File Data Streams

In media spaces, video is often stored in a frame-per-file format. When
dealing with uncompressed realtime HD video streams in this format, it is
crucial that files do not get fragmented and that multiple files a placed
contiguously on disk.

When multiple streams are being ingested and played out at the same time,
it is critical that the filesystem does not cross the streams and
interleave them together as this creates seek and readahead cache miss
latency and prevents both ingest and playout from meeting frame rate
targets.

This patch set creates a "stream of files" concept into the allocator to
place all the data from a single stream contiguously on disk so that RAID
array readahead can be used effectively. Each additional stream gets
placed in different allocation groups within the filesystem, thereby
ensuring that we don't cross any streams. When an AG fills up, we select a
new AG for the stream that is not in use.

The core of the functionality is the stream tracking - each inode that we
create in a directory needs to be associated with the directories' stream.
Hence every time we create a file, we look up the directories' stream
object and associate the new file with that object.

Once we have a stream object for a file, we use the AG that the stream
object point to for allocations. If we can't allocate in that AG (e.g. it
is full) we move the entire stream to another AG. Other inodes in the same
stream are moved to the new AG on their next allocation (i.e. lazy
update).

Stream objects are kept in a cache and hold a reference on the inode.
Hence the inode cannot be reclaimed while there is an outstanding stream
reference. This means that on unlink we need to remove the stream
association and we also need to flush all the associations on certain
events that want to reclaim all unreferenced inodes (e.g. filesystem
freeze).

SGI-PV: 964469
SGI-Modid: xfs-linux-melb:xfs-kern:29096a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Barry Naujok <bnaujok@sgi.com>
Signed-off-by: Donald Douwsma <donaldd@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Vlad Apostolov <vapo@sgi.com>

1 files changed, 136 insertions, 0 deletions

diff --git a/fs/xfs/xfs_filestream.h b/fs/xfs/xfs_filestream.h
new file mode 100644
index 000000000000..f655f7dc334c
--- /dev/null
+++ b/fs/xfs/xfs_filestream.h
@@ -0,0 +1,136 @@
+/*
+ * Copyright (c) 2006-2007 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+#ifndef __XFS_FILESTREAM_H__
+#define __XFS_FILESTREAM_H__
+
+#ifdef __KERNEL__
+
+struct xfs_mount;
+struct xfs_inode;
+struct xfs_perag;
+struct xfs_bmalloca;
+
+#ifdef XFS_FILESTREAMS_TRACE
+#define XFS_FSTRM_KTRACE_INFO           1
+#define XFS_FSTRM_KTRACE_AGSCAN         2
+#define XFS_FSTRM_KTRACE_AGPICK1        3
+#define XFS_FSTRM_KTRACE_AGPICK2        4
+#define XFS_FSTRM_KTRACE_UPDATE         5
+#define XFS_FSTRM_KTRACE_FREE           6
+#define XFS_FSTRM_KTRACE_ITEM_LOOKUP    7
+#define XFS_FSTRM_KTRACE_ASSOCIATE      8
+#define XFS_FSTRM_KTRACE_MOVEAG         9
+#define XFS_FSTRM_KTRACE_ORPHAN         10
+
+#define XFS_FSTRM_KTRACE_SIZE   16384
+extern ktrace_t *xfs_filestreams_trace_buf;
+
+#endif
+
+/*
+ * Allocation group filestream associations are tracked with per-ag atomic
+ * counters.  These counters allow _xfs_filestream_pick_ag() to tell whether a
+ * particular AG already has active filestreams associated with it. The mount
+ * point's m_peraglock is used to protect these counters from per-ag array
+ * re-allocation during a growfs operation.  When xfs_growfs_data_private() is
+ * about to reallocate the array, it calls xfs_filestream_flush() with the
+ * m_peraglock held in write mode.
+ *
+ * Since xfs_mru_cache_flush() guarantees that all the free functions for all
+ * the cache elements have finished executing before it returns, it's safe for
+ * the free functions to use the atomic counters without m_peraglock protection.
+ * This allows the implementation of xfs_fstrm_free_func() to be agnostic about
+ * whether it was called with the m_peraglock held in read mode, write mode or
+ * not held at all.  The race condition this addresses is the following:
+ *
+ *  - The work queue scheduler fires and pulls a filestream directory cache
+ *    element off the LRU end of the cache for deletion, then gets pre-empted.
+ *  - A growfs operation grabs the m_peraglock in write mode, flushes all the
+ *    remaining items from the cache and reallocates the mount point's per-ag
+ *    array, resetting all the counters to zero.
+ *  - The work queue thread resumes and calls the free function for the element
+ *    it started cleaning up earlier.  In the process it decrements the
+ *    filestreams counter for an AG that now has no references.
+ *
+ * With a shrinkfs feature, the above scenario could panic the system.
+ *
+ * All other uses of the following macros should be protected by either the
+ * m_peraglock held in read mode, or the cache's internal locking exposed by the
+ * interval between a call to xfs_mru_cache_lookup() and a call to
+ * xfs_mru_cache_done().  In addition, the m_peraglock must be held in read mode
+ * when new elements are added to the cache.
+ *
+ * Combined, these locking rules ensure that no associations will ever exist in
+ * the cache that reference per-ag array elements that have since been
+ * reallocated.
+ */
+STATIC_INLINE int
+xfs_filestream_peek_ag(
+        xfs_mount_t     *mp,
+        xfs_agnumber_t  agno)
+{
+        return atomic_read(&mp->m_perag[agno].pagf_fstrms);
+}
+
+STATIC_INLINE int
+xfs_filestream_get_ag(
+        xfs_mount_t     *mp,
+        xfs_agnumber_t  agno)
+{
+        return atomic_inc_return(&mp->m_perag[agno].pagf_fstrms);
+}
+
+STATIC_INLINE int
+xfs_filestream_put_ag(
+        xfs_mount_t     *mp,
+        xfs_agnumber_t  agno)
+{
+        return atomic_dec_return(&mp->m_perag[agno].pagf_fstrms);
+}
+
+/* allocation selection flags */
+typedef enum xfs_fstrm_alloc {
+        XFS_PICK_USERDATA = 1,
+        XFS_PICK_LOWSPACE = 2,
+} xfs_fstrm_alloc_t;
+
+/* prototypes for filestream.c */
+int xfs_filestream_init(void);
+void xfs_filestream_uninit(void);
+int xfs_filestream_mount(struct xfs_mount *mp);
+void xfs_filestream_unmount(struct xfs_mount *mp);
+void xfs_filestream_flush(struct xfs_mount *mp);
+xfs_agnumber_t xfs_filestream_lookup_ag(struct xfs_inode *ip);
+int xfs_filestream_associate(struct xfs_inode *dip, struct xfs_inode *ip);
+void xfs_filestream_deassociate(struct xfs_inode *ip);
+int xfs_filestream_new_ag(struct xfs_bmalloca *ap, xfs_agnumber_t *agp);
+
+
+/* filestreams for the inode? */
+STATIC_INLINE int
+xfs_inode_is_filestream(
+        struct xfs_inode        *ip)
+{
+        return (ip->i_mount->m_flags & XFS_MOUNT_FILESTREAMS) ||
+                xfs_iflags_test(ip, XFS_IFILESTREAM) ||
+                (ip->i_d.di_flags & XFS_DIFLAG_FILESTREAM);
+}
+
+#endif /* __KERNEL__ */
+
+#endif /* __XFS_FILESTREAM_H__ */