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Lazy Superblock Counters

When we have a couple of hundred transactions on the fly at once,
they all typically modify the on disk superblock in some way.
create/unclink/mkdir/rmdir modify inode counts, allocation/freeing
modify free block counts.

When these counts are modified in a transaction, the must eventually
lock the superblock buffer and apply the mods.  The buffer then
remains locked until the transaction is committed into the incore
log buffer. The result of this is that with enough transactions on
the fly the incore superblock buffer becomes a bottleneck.

The result of contention on the incore superblock buffer is that
transaction rates fall - the more pressure that is put on the
superblock buffer, the slower things go.

The key to removing the contention is to not require the superblock
fields in question to be locked. We do that by not marking the
superblock dirty in the transaction. IOWs, we modify the incore
superblock but do not modify the cached superblock buffer. In short,
we do not log superblock modifications to critical fields in the
superblock on every transaction. In fact we only do it just before
we write the superblock to disk every sync period or just before
unmount.

This creates an interesting problem - if we don't log or write out
the fields in every transaction, then how do the values get
recovered after a crash? the answer is simple - we keep enough
duplicate, logged information in other structures that we can
reconstruct the correct count  after log recovery has been
performed.

It is the AGF and AGI structures that contain the duplicate
information; after recovery, we walk every AGI and AGF and sum their
individual counters to get the correct value, and we do a
transaction into the log to correct them. An optimisation of this is
that if we have a clean unmount record, we know the value in the
superblock is correct, so we can avoid the summation walk under
normal conditions and so mount/recovery times do not change under
normal operation.

One wrinkle that was discovered during development was that the
blocks used in the freespace btrees are never accounted for in the
AGF counters. This was once a valid optimisation to make; when the
filesystem is full, the free space btrees are empty and consume no
space. Hence when it matters, the "accounting" is correct.  But that
means the when we do the AGF summations, we would not have a correct
count and xfs_check would complain.  Hence a new counter was added
to track the number of blocks used by the free space btrees. This is
an *on-disk format change*.

As a result of this, lazy superblock counters are a mkfs option
and at the moment on linux there is no way to convert an old
filesystem. This is possible - xfs_db can be used to twiddle the
right bits and then xfs_repair will do the format conversion
for you. Similarly, you can convert backwards as well. At some point
we'll add functionality to xfs_admin to do the bit twiddling
easily....
Merge of xfs-linux-melb:xfs-kern:28652a by kenmcd.

  Changes to support lazy superblock counters.

/*
 * Copyright (c) 2000-2006 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_VFS_H__
#define __XFS_VFS_H__

#include <linux/vfs.h>
#include "xfs_fs.h"

struct bhv_vfs;
struct bhv_vnode;

struct fid;
struct cred;
struct seq_file;
struct super_block;
struct xfs_mount_args;

typedef struct kstatfs	bhv_statvfs_t;

typedef struct bhv_vfs_sync_work {
	struct list_head	w_list;
	struct bhv_vfs		*w_vfs;
	void			*w_data;	/* syncer routine argument */
	void			(*w_syncer)(struct bhv_vfs *, void *);
} bhv_vfs_sync_work_t;

typedef struct bhv_vfs {
	u_int			vfs_flag;	/* flags */
	xfs_fsid_t		vfs_fsid;	/* file system ID */
	xfs_fsid_t		*vfs_altfsid;	/* An ID fixed for life of FS */
	bhv_head_t		vfs_bh;		/* head of vfs behavior chain */
	struct super_block	*vfs_super;	/* generic superblock pointer */
	struct task_struct	*vfs_sync_task;	/* generalised sync thread */
	bhv_vfs_sync_work_t	vfs_sync_work;	/* work item for VFS_SYNC */
	struct list_head	vfs_sync_list;	/* sync thread work item list */
	spinlock_t		vfs_sync_lock;	/* work item list lock */
	int			vfs_sync_seq;	/* sync thread generation no. */
	wait_queue_head_t	vfs_wait_single_sync_task;
} bhv_vfs_t;

#define bhvtovfs(bdp)		( (struct bhv_vfs *)BHV_VOBJ(bdp) )
#define bhvtovfsops(bdp)	( (struct bhv_vfsops *)BHV_OPS(bdp) )
#define VFS_BHVHEAD(vfs)	( &(vfs)->vfs_bh )
#define VFS_REMOVEBHV(vfs, bdp)	( bhv_remove(VFS_BHVHEAD(vfs), bdp) )

#define VFS_POSITION_BASE	BHV_POSITION_BASE	/* chain bottom */
#define VFS_POSITION_TOP	BHV_POSITION_TOP	/* chain top */
#define VFS_POSITION_INVALID	BHV_POSITION_INVALID	/* invalid pos. num */

typedef enum {
	VFS_BHV_UNKNOWN,	/* not specified */
	VFS_BHV_XFS,		/* xfs */
	VFS_BHV_DM,		/* data migration */
	VFS_BHV_QM,		/* quota manager */
	VFS_BHV_IO,		/* IO path */
	VFS_BHV_END		/* housekeeping end-of-range */
} bhv_vfs_type_t;

#define VFS_POSITION_XFS	(BHV_POSITION_BASE)
#define VFS_POSITION_DM		(VFS_POSITION_BASE+10)
#define VFS_POSITION_QM		(VFS_POSITION_BASE+20)
#define VFS_POSITION_IO		(VFS_POSITION_BASE+30)

#define VFS_RDONLY		0x0001	/* read-only vfs */
#define VFS_GRPID		0x0002	/* group-ID assigned from directory */
#define VFS_DMI			0x0004	/* filesystem has the DMI enabled */
/* ---- VFS_UMOUNT ----		0x0008	-- unneeded, fixed via kthread APIs */
#define VFS_32BITINODES		0x0010	/* do not use inums above 32 bits */
#define VFS_END			0x0010	/* max flag */

#define SYNC_ATTR		0x0001	/* sync attributes */
#define SYNC_CLOSE		0x0002	/* close file system down */
#define SYNC_DELWRI		0x0004	/* look at delayed writes */
#define SYNC_WAIT		0x0008	/* wait for i/o to complete */
#define SYNC_BDFLUSH		0x0010	/* BDFLUSH is calling -- don't block */
#define SYNC_FSDATA		0x0020	/* flush fs data (e.g. superblocks) */
#define SYNC_REFCACHE		0x0040  /* prune some of the nfs ref cache */
#define SYNC_REMOUNT		0x0080  /* remount readonly, no dummy LRs */
#define SYNC_IOWAIT		0x0100  /* wait for all I/O to complete */
#define SYNC_SUPER		0x0200  /* flush superblock to disk */

#define SHUTDOWN_META_IO_ERROR	0x0001	/* write attempt to metadata failed */
#define SHUTDOWN_LOG_IO_ERROR	0x0002	/* write attempt to the log failed */
#define SHUTDOWN_FORCE_UMOUNT	0x0004	/* shutdown from a forced unmount */
#define SHUTDOWN_CORRUPT_INCORE	0x0008	/* corrupt in-memory data structures */
#define SHUTDOWN_REMOTE_REQ	0x0010	/* shutdown came from remote cell */
#define SHUTDOWN_DEVICE_REQ	0x0020	/* failed all paths to the device */

typedef int	(*vfs_mount_t)(bhv_desc_t *,
				struct xfs_mount_args *, struct cred *);
typedef int	(*vfs_parseargs_t)(bhv_desc_t *, char *,
				struct xfs_mount_args *, int);
typedef	int	(*vfs_showargs_t)(bhv_desc_t *, struct seq_file *);
typedef int	(*vfs_unmount_t)(bhv_desc_t *, int, struct cred *);
typedef int	(*vfs_mntupdate_t)(bhv_desc_t *, int *,
				struct xfs_mount_args *);
typedef int	(*vfs_root_t)(bhv_desc_t *, struct bhv_vnode **);
typedef int	(*vfs_statvfs_t)(bhv_desc_t *, bhv_statvfs_t *,
				struct bhv_vnode *);
typedef int	(*vfs_sync_t)(bhv_desc_t *, int, struct cred *);
typedef int	(*vfs_vget_t)(bhv_desc_t *, struct bhv_vnode **, struct fid *);
typedef int	(*vfs_dmapiops_t)(bhv_desc_t *, caddr_t);
typedef int	(*vfs_quotactl_t)(bhv_desc_t *, int, int, caddr_t);
typedef void	(*vfs_init_vnode_t)(bhv_desc_t *,
				struct bhv_vnode *, bhv_desc_t *, int);
typedef void	(*vfs_force_shutdown_t)(bhv_desc_t *, int, char *, int);
typedef void	(*vfs_freeze_t)(bhv_desc_t *);
typedef	struct inode * (*vfs_get_inode_t)(bhv_desc_t *, xfs_ino_t, int);

typedef struct bhv_vfsops {
	bhv_position_t		vf_position;	/* behavior chain position */
	vfs_mount_t		vfs_mount;	/* mount file system */
	vfs_parseargs_t		vfs_parseargs;	/* parse mount options */
	vfs_showargs_t		vfs_showargs;	/* unparse mount options */
	vfs_unmount_t		vfs_unmount;	/* unmount file system */
	vfs_mntupdate_t		vfs_mntupdate;	/* update file system options */
	vfs_root_t		vfs_root;	/* get root vnode */
	vfs_statvfs_t		vfs_statvfs;	/* file system statistics */
	vfs_sync_t		vfs_sync;	/* flush files */
	vfs_vget_t		vfs_vget;	/* get vnode from fid */
	vfs_dmapiops_t		vfs_dmapiops;	/* data migration */
	vfs_quotactl_t		vfs_quotactl;	/* disk quota */
	vfs_get_inode_t		vfs_get_inode;	/* bhv specific iget */
	vfs_init_vnode_t	vfs_init_vnode;	/* initialize a new vnode */
	vfs_force_shutdown_t	vfs_force_shutdown;	/* crash and burn */
	vfs_freeze_t		vfs_freeze;	/* freeze fs for snapshot */
} bhv_vfsops_t;

/*
 * Virtual filesystem operations, operating from head bhv.
 */
#define VFSHEAD(v)			((v)->vfs_bh.bh_first)
#define bhv_vfs_mount(v, ma,cr)		vfs_mount(VFSHEAD(v), ma,cr)
#define bhv_vfs_parseargs(v, o,ma,f)	vfs_parseargs(VFSHEAD(v), o,ma,f)
#define bhv_vfs_showargs(v, m)		vfs_showargs(VFSHEAD(v), m)
#define bhv_vfs_unmount(v, f,cr)	vfs_unmount(VFSHEAD(v), f,cr)
#define bhv_vfs_mntupdate(v, fl,args)	vfs_mntupdate(VFSHEAD(v), fl,args)
#define bhv_vfs_root(v, vpp)		vfs_root(VFSHEAD(v), vpp)
#define bhv_vfs_statvfs(v, sp,vp)	vfs_statvfs(VFSHEAD(v), sp,vp)
#define bhv_vfs_sync(v, flag,cr)	vfs_sync(VFSHEAD(v), flag,cr)
#define bhv_vfs_vget(v, vpp,fidp)	vfs_vget(VFSHEAD(v), vpp,fidp)
#define bhv_vfs_dmapiops(v, p)		vfs_dmapiops(VFSHEAD(v), p)
#define bhv_vfs_quotactl(v, c,id,p)	vfs_quotactl(VFSHEAD(v), c,id,p)
#define bhv_vfs_get_inode(v, ino, fl)	vfs_get_inode(VFSHEAD(v), ino,fl)
#define bhv_vfs_init_vnode(v, vp,b,ul)	vfs_init_vnode(VFSHEAD(v), vp,b,ul)
#define bhv_vfs_force_shutdown(v,u,f,l)	vfs_force_shutdown(VFSHEAD(v), u,f,l)
#define bhv_vfs_freeze(v)		vfs_freeze(VFSHEAD(v))

/*
 * Virtual filesystem operations, operating from next bhv.
 */
#define bhv_next_vfs_mount(b, ma,cr)		vfs_mount(b, ma,cr)
#define bhv_next_vfs_parseargs(b, o,ma,f)	vfs_parseargs(b, o,ma,f)
#define bhv_next_vfs_showargs(b, m)		vfs_showargs(b, m)
#define bhv_next_vfs_unmount(b, f,cr)		vfs_unmount(b, f,cr)
#define bhv_next_vfs_mntupdate(b, fl,args)	vfs_mntupdate(b, fl, args)
#define bhv_next_vfs_root(b, vpp)		vfs_root(b, vpp)
#define bhv_next_vfs_statvfs(b, sp,vp)		vfs_statvfs(b, sp,vp)
#define bhv_next_vfs_sync(b, flag,cr)		vfs_sync(b, flag,cr)
#define bhv_next_vfs_vget(b, vpp,fidp)		vfs_vget(b, vpp,fidp)
#define bhv_next_vfs_dmapiops(b, p)		vfs_dmapiops(b, p)
#define bhv_next_vfs_quotactl(b, c,id,p)	vfs_quotactl(b, c,id,p)
#define bhv_next_vfs_get_inode(b, ino,fl)	vfs_get_inode(b, ino,fl)
#define bhv_next_vfs_init_vnode(b, vp,b2,ul)	vfs_init_vnode(b, vp,b2,ul)
#define bhv_next_force_shutdown(b, fl,f,l)	vfs_force_shutdown(b, fl,f,l)
#define bhv_next_vfs_freeze(b)			vfs_freeze(b)

extern int vfs_mount(bhv_desc_t *, struct xfs_mount_args *, struct cred *);
extern int vfs_parseargs(bhv_desc_t *, char *, struct xfs_mount_args *, int);
extern int vfs_showargs(bhv_desc_t *, struct seq_file *);
extern int vfs_unmount(bhv_desc_t *, int, struct cred *);
extern int vfs_mntupdate(bhv_desc_t *, int *, struct xfs_mount_args *);
extern int vfs_root(bhv_desc_t *, struct bhv_vnode **);
extern int vfs_statvfs(bhv_desc_t *, bhv_statvfs_t *, struct bhv_vnode *);
extern int vfs_sync(bhv_desc_t *, int, struct cred *);
extern int vfs_vget(bhv_desc_t *, struct bhv_vnode **, struct fid *);
extern int vfs_dmapiops(bhv_desc_t *, caddr_t);
extern int vfs_quotactl(bhv_desc_t *, int, int, caddr_t);
extern struct inode *vfs_get_inode(bhv_desc_t *, xfs_ino_t, int);
extern void vfs_init_vnode(bhv_desc_t *, struct bhv_vnode *, bhv_desc_t *, int);
extern void vfs_force_shutdown(bhv_desc_t *, int, char *, int);
extern void vfs_freeze(bhv_desc_t *);

#define vfs_test_for_freeze(vfs)	((vfs)->vfs_super->s_frozen)
#define vfs_wait_for_freeze(vfs,l)	vfs_check_frozen((vfs)->vfs_super, (l))

#define XFS_DMOPS		"xfs_dm_operations"	/* Data Migration */
#define XFS_QMOPS		"xfs_qm_operations"	/* Quota Manager  */
#define XFS_IOOPS		"xfs_io_operations"	/* I/O subsystem  */
#define XFS_DM_MODULE		"xfs_dmapi"
#define XFS_QM_MODULE		"xfs_quota"
#define XFS_IO_MODULE		"xfs_ioops"

typedef struct bhv_module_vfsops {
	struct bhv_vfsops	bhv_common;
	void *			bhv_custom;
} bhv_module_vfsops_t;

typedef struct bhv_module {
	bhv_desc_t		bm_desc;
	const char *		bm_name;
	bhv_module_vfsops_t *	bm_ops;
} bhv_module_t;

#define vfs_bhv_lookup(v, id)	(bhv_lookup_range(&(v)->vfs_bh, (id), (id)))
#define vfs_bhv_custom(b)	(((bhv_module_vfsops_t*)BHV_OPS(b))->bhv_custom)
#define vfs_bhv_set_custom(b,o)	((b)->bhv_custom = (void *)(o))
#define vfs_bhv_clr_custom(b)	((b)->bhv_custom = NULL)

extern bhv_vfs_t *vfs_allocate(struct super_block *);
extern bhv_vfs_t *vfs_from_sb(struct super_block *);
extern void vfs_deallocate(bhv_vfs_t *);
extern void vfs_insertbhv(bhv_vfs_t *, bhv_desc_t *, bhv_vfsops_t *, void *);

extern void bhv_module_init(const char *, struct module *, const void *);
extern void bhv_module_exit(const char *);
extern void bhv_get_vfsops(struct bhv_vfs *, const char *, const char *);
extern void bhv_insert_all_vfsops(struct bhv_vfs *);
extern void bhv_remove_all_vfsops(struct bhv_vfs *, int);
extern void bhv_remove_vfsops(struct bhv_vfs *, int);

#endif	/* __XFS_VFS_H__ */