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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).
Merge of xfs-linux-melb:xfs-kern:29096a by kenmcd.

  Concurrent Multi-File Data Streams feature check in.

/*
 * 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_MRU_CACHE_H__
#define __XFS_MRU_CACHE_H__


/* Function pointer type for callback to free a client's data pointer. */
typedef void (*xfs_mru_cache_free_func_t)(unsigned long, void*);

typedef struct xfs_mru_cache
{
	struct radix_tree_root	store;     /* Core storage data structure.  */
	struct list_head	*lists;    /* Array of lists, one per grp.  */
	struct list_head	reap_list; /* Elements overdue for reaping. */
	spinlock_t		lock;      /* Lock to protect this struct.  */
	unsigned int		grp_count; /* Number of discrete groups.    */
	unsigned int		grp_time;  /* Time period spanned by grps.  */
	unsigned int		lru_grp;   /* Group containing time zero.   */
	unsigned long		time_zero; /* Time first element was added. */
	unsigned long		next_reap; /* Time that the reaper should
					      next do something. */
	unsigned int		reap_all;  /* if set, reap all lists */
	xfs_mru_cache_free_func_t free_func; /* Function pointer for freeing. */
	struct delayed_work	work;      /* Workqueue data for reaping.   */
} xfs_mru_cache_t;

int xfs_mru_cache_init(void);
void xfs_mru_cache_uninit(void);
int xfs_mru_cache_create(struct xfs_mru_cache **mrup, unsigned int lifetime_ms,
			     unsigned int grp_count,
			     xfs_mru_cache_free_func_t free_func);
void xfs_mru_cache_flush(xfs_mru_cache_t *mru, int restart);
void xfs_mru_cache_destroy(struct xfs_mru_cache *mru);
int xfs_mru_cache_insert(struct xfs_mru_cache *mru, unsigned long key,
				void *value);
void * xfs_mru_cache_remove(struct xfs_mru_cache *mru, unsigned long key);
void xfs_mru_cache_delete(struct xfs_mru_cache *mru, unsigned long key);
void *xfs_mru_cache_lookup(struct xfs_mru_cache *mru, unsigned long key);
void *xfs_mru_cache_peek(struct xfs_mru_cache *mru, unsigned long key);
void xfs_mru_cache_done(struct xfs_mru_cache *mru);

#endif /* __XFS_MRU_CACHE_H__ */