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mirror_zfs/include/sys/arc.h
Brian Behlendorf ab26409db7 Linux 3.1 compat, super_block->s_shrink 
The Linux 3.1 kernel has introduced the concept of per-filesystem
shrinkers which are directly assoicated with a super block.  Prior
to this change there was one shared global shrinker.

The zfs code relied on being able to call the global shrinker when
the arc_meta_limit was exceeded.  This would cause the VFS to drop
references on a fraction of the dentries in the dcache.  The ARC
could then safely reclaim the memory used by these entries and
honor the arc_meta_limit.  Unfortunately, when per-filesystem
shrinkers were added the old interfaces were made unavailable.

This change adds support to use the new per-filesystem shrinker
interface so we can continue to honor the arc_meta_limit.  The
major benefit of the new interface is that we can now target
only the zfs filesystem for dentry and inode pruning.  Thus we
can minimize any impact on the caching of other filesystems.

In the context of making this change several other important
issues related to managing the ARC were addressed, they include:

* The dnlc_reduce_cache() function which was called by the ARC
to drop dentries for the Posix layer was replaced with a generic
zfs_prune_t callback.  The ZPL layer now registers a callback to
drop these dentries removing a layering violation which dates
back to the Solaris code.  This callback can also be used by
other ARC consumers such as Lustre.

  arc_add_prune_callback()
  arc_remove_prune_callback()

* The arc_reduce_dnlc_percent module option has been changed to
arc_meta_prune for clarity.  The dnlc functions are specific to
Solaris's VFS and have already been largely eliminated already.
The replacement tunable now represents the number of bytes the
prune callback will request when invoked.

* Less aggressively invoke the prune callback.  We used to call
this whenever we exceeded the arc_meta_limit however that's not
strictly correct since it results in over zeleous reclaim of
dentries and inodes.  It is now only called once the arc_meta_limit
is exceeded and every effort has been made to evict other data from
the ARC cache.

* More promptly manage exceeding the arc_meta_limit.  When reading
meta data in to the cache if a buffer was unable to be recycled
notify the arc_reclaim thread to invoke the required prune.

* Added arcstat_prune kstat which is incremented when the ARC
is forced to request that a consumer prune its cache.  Remember
this will only occur when the ARC has no other choice.  If it
can evict buffers safely without invoking the prune callback
it will.

* This change is also expected to resolve the unexpect collapses
of the ARC cache.  This would occur because when exceeded just the
arc_meta_limit reclaim presure would be excerted on the arc_c
value via arc_shrink().  This effectively shrunk the entire cache
when really we just needed to reclaim meta data.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #466
Closes #292
2012-01-11 11:46:02 -08:00

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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
*/
#ifndef _SYS_ARC_H
#define _SYS_ARC_H
#include <sys/zfs_context.h>
#ifdef __cplusplus
extern "C" {
#endif
#include <sys/zio.h>
#include <sys/dmu.h>
#include <sys/spa.h>
#include <sys/refcount.h>
typedef struct arc_buf_hdr arc_buf_hdr_t;
typedef struct arc_buf arc_buf_t;
typedef struct arc_prune arc_prune_t;
typedef void arc_done_func_t(zio_t *zio, arc_buf_t *buf, void *private);
typedef void arc_prune_func_t(int64_t bytes, void *private);
typedef int arc_evict_func_t(void *private);
/* generic arc_done_func_t's which you can use */
arc_done_func_t arc_bcopy_func;
arc_done_func_t arc_getbuf_func;
/* generic arc_prune_func_t wrapper for callbacks */
struct arc_prune {
arc_prune_func_t *p_pfunc;
void *p_private;
list_node_t p_node;
refcount_t p_refcnt;
};
struct arc_buf {
arc_buf_hdr_t *b_hdr;
arc_buf_t *b_next;
kmutex_t b_evict_lock;
krwlock_t b_data_lock;
void *b_data;
arc_evict_func_t *b_efunc;
void *b_private;
};
typedef enum arc_buf_contents {
ARC_BUFC_DATA, /* buffer contains data */
ARC_BUFC_METADATA, /* buffer contains metadata */
ARC_BUFC_NUMTYPES
} arc_buf_contents_t;
/*
* These are the flags we pass into calls to the arc
*/
#define ARC_WAIT (1 << 1) /* perform I/O synchronously */
#define ARC_NOWAIT (1 << 2) /* perform I/O asynchronously */
#define ARC_PREFETCH (1 << 3) /* I/O is a prefetch */
#define ARC_CACHED (1 << 4) /* I/O was already in cache */
#define ARC_L2CACHE (1 << 5) /* cache in L2ARC */
/*
* The following breakdows of arc_size exist for kstat only.
*/
typedef enum arc_space_type {
ARC_SPACE_DATA,
ARC_SPACE_HDRS,
ARC_SPACE_L2HDRS,
ARC_SPACE_OTHER,
ARC_SPACE_NUMTYPES
} arc_space_type_t;
void arc_space_consume(uint64_t space, arc_space_type_t type);
void arc_space_return(uint64_t space, arc_space_type_t type);
void *arc_data_buf_alloc(uint64_t space);
void arc_data_buf_free(void *buf, uint64_t space);
arc_buf_t *arc_buf_alloc(spa_t *spa, int size, void *tag,
arc_buf_contents_t type);
arc_buf_t *arc_loan_buf(spa_t *spa, int size);
void arc_return_buf(arc_buf_t *buf, void *tag);
void arc_loan_inuse_buf(arc_buf_t *buf, void *tag);
void arc_buf_add_ref(arc_buf_t *buf, void *tag);
int arc_buf_remove_ref(arc_buf_t *buf, void *tag);
int arc_buf_size(arc_buf_t *buf);
void arc_release(arc_buf_t *buf, void *tag);
int arc_release_bp(arc_buf_t *buf, void *tag, blkptr_t *bp, spa_t *spa,
zbookmark_t *zb);
int arc_released(arc_buf_t *buf);
int arc_has_callback(arc_buf_t *buf);
void arc_buf_freeze(arc_buf_t *buf);
void arc_buf_thaw(arc_buf_t *buf);
#ifdef ZFS_DEBUG
int arc_referenced(arc_buf_t *buf);
#endif
int arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp, arc_buf_t *pbuf,
arc_done_func_t *done, void *private, int priority, int zio_flags,
uint32_t *arc_flags, const zbookmark_t *zb);
int arc_read_nolock(zio_t *pio, spa_t *spa, const blkptr_t *bp,
arc_done_func_t *done, void *private, int priority, int flags,
uint32_t *arc_flags, const zbookmark_t *zb);
zio_t *arc_write(zio_t *pio, spa_t *spa, uint64_t txg,
blkptr_t *bp, arc_buf_t *buf, boolean_t l2arc, const zio_prop_t *zp,
arc_done_func_t *ready, arc_done_func_t *done, void *private,
int priority, int zio_flags, const zbookmark_t *zb);
arc_prune_t *arc_add_prune_callback(arc_prune_func_t *func, void *private);
void arc_remove_prune_callback(arc_prune_t *p);
void arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private);
int arc_buf_evict(arc_buf_t *buf);
void arc_adjust_meta(int64_t adjustment, boolean_t may_prune);
void arc_flush(spa_t *spa);
void arc_tempreserve_clear(uint64_t reserve);
int arc_tempreserve_space(uint64_t reserve, uint64_t txg);
void arc_init(void);
void arc_fini(void);
/*
* Level 2 ARC
*/
void l2arc_add_vdev(spa_t *spa, vdev_t *vd);
void l2arc_remove_vdev(vdev_t *vd);
boolean_t l2arc_vdev_present(vdev_t *vd);
void l2arc_init(void);
void l2arc_fini(void);
void l2arc_start(void);
void l2arc_stop(void);
#ifdef __cplusplus
}
#endif
#endif /* _SYS_ARC_H */
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