[linux-2.6-block.git] / fs / xfs / libxfs / xfs_ag_resv.c

/*
 * Copyright (C) 2016 Oracle.  All Rights Reserved.
 *
 * Author: Darrick J. Wong <darrick.wong@oracle.com>
 *
 * 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; either version 2
 * of the License, or (at your option) any later version.
 *
 * 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.
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_sb.h"
#include "xfs_mount.h"
#include "xfs_defer.h"
#include "xfs_alloc.h"
#include "xfs_error.h"
#include "xfs_trace.h"
#include "xfs_cksum.h"
#include "xfs_trans.h"
#include "xfs_bit.h"
#include "xfs_bmap.h"
#include "xfs_bmap_btree.h"
#include "xfs_ag_resv.h"
#include "xfs_trans_space.h"
#include "xfs_rmap_btree.h"
#include "xfs_btree.h"
#include "xfs_refcount_btree.h"

/*
 * Per-AG Block Reservations
 *
 * For some kinds of allocation group metadata structures, it is advantageous
 * to reserve a small number of blocks in each AG so that future expansions of
 * that data structure do not encounter ENOSPC because errors during a btree
 * split cause the filesystem to go offline.
 *
 * Prior to the introduction of reflink, this wasn't an issue because the free
 * space btrees maintain a reserve of space (the AGFL) to handle any expansion
 * that may be necessary; and allocations of other metadata (inodes, BMBT,
 * dir/attr) aren't restricted to a single AG.  However, with reflink it is
 * possible to allocate all the space in an AG, have subsequent reflink/CoW
 * activity expand the refcount btree, and discover that there's no space left
 * to handle that expansion.  Since we can calculate the maximum size of the
 * refcount btree, we can reserve space for it and avoid ENOSPC.
 *
 * Handling per-AG reservations consists of three changes to the allocator's
 * behavior:  First, because these reservations are always needed, we decrease
 * the ag_max_usable counter to reflect the size of the AG after the reserved
 * blocks are taken.  Second, the reservations must be reflected in the
 * fdblocks count to maintain proper accounting.  Third, each AG must maintain
 * its own reserved block counter so that we can calculate the amount of space
 * that must remain free to maintain the reservations.  Fourth, the "remaining
 * reserved blocks" count must be used when calculating the length of the
 * longest free extent in an AG and to clamp maxlen in the per-AG allocation
 * functions.  In other words, we maintain a virtual allocation via in-core
 * accounting tricks so that we don't have to clean up after a crash. :)
 *
 * Reserved blocks can be managed by passing one of the enum xfs_ag_resv_type
 * values via struct xfs_alloc_arg or directly to the xfs_free_extent
 * function.  It might seem a little funny to maintain a reservoir of blocks
 * to feed another reservoir, but the AGFL only holds enough blocks to get
 * through the next transaction.  The per-AG reservation is to ensure (we
 * hope) that each AG never runs out of blocks.  Each data structure wanting
 * to use the reservation system should update ask/used in xfs_ag_resv_init.
 */

/*
 * Are we critically low on blocks?  For now we'll define that as the number
 * of blocks we can get our hands on being less than 10% of what we reserved
 * or less than some arbitrary number (maximum btree height).
 */
bool
xfs_ag_resv_critical(
	struct xfs_perag		*pag,
	enum xfs_ag_resv_type		type)
{
	xfs_extlen_t			avail;
	xfs_extlen_t			orig;

	switch (type) {
	case XFS_AG_RESV_METADATA:
		avail = pag->pagf_freeblks - pag->pag_agfl_resv.ar_reserved;
		orig = pag->pag_meta_resv.ar_asked;
		break;
	case XFS_AG_RESV_AGFL:
		avail = pag->pagf_freeblks + pag->pagf_flcount -
			pag->pag_meta_resv.ar_reserved;
		orig = pag->pag_agfl_resv.ar_asked;
		break;
	default:
		ASSERT(0);
		return false;
	}

	trace_xfs_ag_resv_critical(pag, type, avail);

	/* Critically low if less than 10% or max btree height remains. */
	return XFS_TEST_ERROR(avail < orig / 10 || avail < XFS_BTREE_MAXLEVELS,
			pag->pag_mount, XFS_ERRTAG_AG_RESV_CRITICAL,
			XFS_RANDOM_AG_RESV_CRITICAL);
}

/*
 * How many blocks are reserved but not used, and therefore must not be
 * allocated away?
 */
xfs_extlen_t
xfs_ag_resv_needed(
	struct xfs_perag		*pag,
	enum xfs_ag_resv_type		type)
{
	xfs_extlen_t			len;

	len = pag->pag_meta_resv.ar_reserved + pag->pag_agfl_resv.ar_reserved;
	switch (type) {
	case XFS_AG_RESV_METADATA:
	case XFS_AG_RESV_AGFL:
		len -= xfs_perag_resv(pag, type)->ar_reserved;
		break;
	case XFS_AG_RESV_NONE:
		/* empty */
		break;
	default:
		ASSERT(0);
	}

	trace_xfs_ag_resv_needed(pag, type, len);

	return len;
}

/* Clean out a reservation */
static int
__xfs_ag_resv_free(
	struct xfs_perag		*pag,
	enum xfs_ag_resv_type		type)
{
	struct xfs_ag_resv		*resv;
	xfs_extlen_t			oldresv;
	int				error;

	trace_xfs_ag_resv_free(pag, type, 0);

	resv = xfs_perag_resv(pag, type);
	pag->pag_mount->m_ag_max_usable += resv->ar_asked;
	/*
	 * AGFL blocks are always considered "free", so whatever
	 * was reserved at mount time must be given back at umount.
	 */
	if (type == XFS_AG_RESV_AGFL)
		oldresv = resv->ar_orig_reserved;
	else
		oldresv = resv->ar_reserved;
	error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
	resv->ar_reserved = 0;
	resv->ar_asked = 0;

	if (error)
		trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
				error, _RET_IP_);
	return error;
}

/* Free a per-AG reservation. */
int
xfs_ag_resv_free(
	struct xfs_perag		*pag)
{
	int				error;
	int				err2;

	error = __xfs_ag_resv_free(pag, XFS_AG_RESV_AGFL);
	err2 = __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
	if (err2 && !error)
		error = err2;
	return error;
}

static int
__xfs_ag_resv_init(
	struct xfs_perag		*pag,
	enum xfs_ag_resv_type		type,
	xfs_extlen_t			ask,
	xfs_extlen_t			used)
{
	struct xfs_mount		*mp = pag->pag_mount;
	struct xfs_ag_resv		*resv;
	int				error;

	resv = xfs_perag_resv(pag, type);
	if (used > ask)
		ask = used;
	resv->ar_asked = ask;
	resv->ar_reserved = resv->ar_orig_reserved = ask - used;
	mp->m_ag_max_usable -= ask;

	trace_xfs_ag_resv_init(pag, type, ask);

	error = xfs_mod_fdblocks(mp, -(int64_t)resv->ar_reserved, true);
	if (error)
		trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
				error, _RET_IP_);

	return error;
}

/* Create a per-AG block reservation. */
int
xfs_ag_resv_init(
	struct xfs_perag		*pag)
{
	xfs_extlen_t			ask;
	xfs_extlen_t			used;
	int				error = 0;

	/* Create the metadata reservation. */
	if (pag->pag_meta_resv.ar_asked == 0) {
		ask = used = 0;

		error = xfs_refcountbt_calc_reserves(pag->pag_mount,
				pag->pag_agno, &ask, &used);
		if (error)
			goto out;

		error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
				ask, used);
		if (error)
			goto out;
	}

	/* Create the AGFL metadata reservation */
	if (pag->pag_agfl_resv.ar_asked == 0) {
		ask = used = 0;

		error = xfs_rmapbt_calc_reserves(pag->pag_mount, pag->pag_agno,
				&ask, &used);
		if (error)
			goto out;

		error = __xfs_ag_resv_init(pag, XFS_AG_RESV_AGFL, ask, used);
		if (error)
			goto out;
	}

	ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
	       xfs_perag_resv(pag, XFS_AG_RESV_AGFL)->ar_reserved <=
	       pag->pagf_freeblks + pag->pagf_flcount);
out:
	return error;
}

/* Allocate a block from the reservation. */
void
xfs_ag_resv_alloc_extent(
	struct xfs_perag		*pag,
	enum xfs_ag_resv_type		type,
	struct xfs_alloc_arg		*args)
{
	struct xfs_ag_resv		*resv;
	xfs_extlen_t			len;
	uint				field;

	trace_xfs_ag_resv_alloc_extent(pag, type, args->len);

	switch (type) {
	case XFS_AG_RESV_METADATA:
	case XFS_AG_RESV_AGFL:
		resv = xfs_perag_resv(pag, type);
		break;
	default:
		ASSERT(0);
		/* fall through */
	case XFS_AG_RESV_NONE:
		field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
				       XFS_TRANS_SB_FDBLOCKS;
		xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
		return;
	}

	len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
	resv->ar_reserved -= len;
	if (type == XFS_AG_RESV_AGFL)
		return;
	/* Allocations of reserved blocks only need on-disk sb updates... */
	xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
	/* ...but non-reserved blocks need in-core and on-disk updates. */
	if (args->len > len)
		xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
				-((int64_t)args->len - len));
}

/* Free a block to the reservation. */
void
xfs_ag_resv_free_extent(
	struct xfs_perag		*pag,
	enum xfs_ag_resv_type		type,
	struct xfs_trans		*tp,
	xfs_extlen_t			len)
{
	xfs_extlen_t			leftover;
	struct xfs_ag_resv		*resv;

	trace_xfs_ag_resv_free_extent(pag, type, len);

	switch (type) {
	case XFS_AG_RESV_METADATA:
	case XFS_AG_RESV_AGFL:
		resv = xfs_perag_resv(pag, type);
		break;
	default:
		ASSERT(0);
		/* fall through */
	case XFS_AG_RESV_NONE:
		xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
		return;
	}

	leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
	resv->ar_reserved += leftover;
	if (type == XFS_AG_RESV_AGFL)
		return;
	/* Freeing into the reserved pool only requires on-disk update... */
	xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
	/* ...but freeing beyond that requires in-core and on-disk update. */
	if (len > leftover)
		xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
}
Commit	Line	Data
3fd129b6 DW	1	/*
	2	* Copyright (C) 2016 Oracle. All Rights Reserved.
	3	*
	4	* Author: Darrick J. Wong <darrick.wong@oracle.com>
	5	*
	6	* This program is free software; you can redistribute it and/or
	7	* modify it under the terms of the GNU General Public License
	8	* as published by the Free Software Foundation; either version 2
	9	* of the License, or (at your option) any later version.
	10	*
	11	* This program is distributed in the hope that it would be useful,
	12	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	13	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	14	* GNU General Public License for more details.
	15	*
	16	* You should have received a copy of the GNU General Public License
	17	* along with this program; if not, write the Free Software Foundation,
	18	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
	19	*/
	20	#include "xfs.h"
	21	#include "xfs_fs.h"
	22	#include "xfs_shared.h"
	23	#include "xfs_format.h"
	24	#include "xfs_log_format.h"
	25	#include "xfs_trans_resv.h"
	26	#include "xfs_sb.h"
	27	#include "xfs_mount.h"
	28	#include "xfs_defer.h"
	29	#include "xfs_alloc.h"
	30	#include "xfs_error.h"
	31	#include "xfs_trace.h"
	32	#include "xfs_cksum.h"
	33	#include "xfs_trans.h"
	34	#include "xfs_bit.h"
	35	#include "xfs_bmap.h"
	36	#include "xfs_bmap_btree.h"
	37	#include "xfs_ag_resv.h"
	38	#include "xfs_trans_space.h"
	39	#include "xfs_rmap_btree.h"
	40	#include "xfs_btree.h"
84d69619	41	#include "xfs_refcount_btree.h"
3fd129b6 DW	42
	43	/*
	44	* Per-AG Block Reservations
	45	*
	46	* For some kinds of allocation group metadata structures, it is advantageous
	47	* to reserve a small number of blocks in each AG so that future expansions of
	48	* that data structure do not encounter ENOSPC because errors during a btree
	49	* split cause the filesystem to go offline.
	50	*
	51	* Prior to the introduction of reflink, this wasn't an issue because the free
	52	* space btrees maintain a reserve of space (the AGFL) to handle any expansion
	53	* that may be necessary; and allocations of other metadata (inodes, BMBT,
	54	* dir/attr) aren't restricted to a single AG. However, with reflink it is
	55	* possible to allocate all the space in an AG, have subsequent reflink/CoW
	56	* activity expand the refcount btree, and discover that there's no space left
	57	* to handle that expansion. Since we can calculate the maximum size of the
	58	* refcount btree, we can reserve space for it and avoid ENOSPC.
	59	*
	60	* Handling per-AG reservations consists of three changes to the allocator's
	61	* behavior: First, because these reservations are always needed, we decrease
	62	* the ag_max_usable counter to reflect the size of the AG after the reserved
	63	* blocks are taken. Second, the reservations must be reflected in the
	64	* fdblocks count to maintain proper accounting. Third, each AG must maintain
	65	* its own reserved block counter so that we can calculate the amount of space
	66	* that must remain free to maintain the reservations. Fourth, the "remaining
	67	* reserved blocks" count must be used when calculating the length of the
	68	* longest free extent in an AG and to clamp maxlen in the per-AG allocation
	69	* functions. In other words, we maintain a virtual allocation via in-core
	70	* accounting tricks so that we don't have to clean up after a crash. :)
	71	*
	72	* Reserved blocks can be managed by passing one of the enum xfs_ag_resv_type
	73	* values via struct xfs_alloc_arg or directly to the xfs_free_extent
	74	* function. It might seem a little funny to maintain a reservoir of blocks
	75	* to feed another reservoir, but the AGFL only holds enough blocks to get
	76	* through the next transaction. The per-AG reservation is to ensure (we
	77	* hope) that each AG never runs out of blocks. Each data structure wanting
	78	* to use the reservation system should update ask/used in xfs_ag_resv_init.
	79	*/
	80
	81	/*
	82	* Are we critically low on blocks? For now we'll define that as the number
	83	* of blocks we can get our hands on being less than 10% of what we reserved
	84	* or less than some arbitrary number (maximum btree height).
	85	*/
	86	bool
	87	xfs_ag_resv_critical(
	88	struct xfs_perag *pag,
	89	enum xfs_ag_resv_type type)
	90	{
	91	xfs_extlen_t avail;
	92	xfs_extlen_t orig;
	93
	94	switch (type) {
	95	case XFS_AG_RESV_METADATA:
	96	avail = pag->pagf_freeblks - pag->pag_agfl_resv.ar_reserved;
	97	orig = pag->pag_meta_resv.ar_asked;
	98	break;
	99	case XFS_AG_RESV_AGFL:
	100	avail = pag->pagf_freeblks + pag->pagf_flcount -
	101	pag->pag_meta_resv.ar_reserved;
	102	orig = pag->pag_agfl_resv.ar_asked;
	103	break;
	104	default:
	105	ASSERT(0);
106	return false;
107	}
108
109	trace_xfs_ag_resv_critical(pag, type, avail);
110
111	/* Critically low if less than 10% or max btree height remains. */
a35eb415 DW	112	return XFS_TEST_ERROR(avail < orig / 10 \|\| avail < XFS_BTREE_MAXLEVELS,
	113	pag->pag_mount, XFS_ERRTAG_AG_RESV_CRITICAL,
	114	XFS_RANDOM_AG_RESV_CRITICAL);
3fd129b6 DW	115	}
	116
	117	/*
	118	* How many blocks are reserved but not used, and therefore must not be
	119	* allocated away?
	120	*/
	121	xfs_extlen_t
	122	xfs_ag_resv_needed(
	123	struct xfs_perag *pag,
	124	enum xfs_ag_resv_type type)
	125	{
	126	xfs_extlen_t len;
	127
	128	len = pag->pag_meta_resv.ar_reserved + pag->pag_agfl_resv.ar_reserved;
	129	switch (type) {
	130	case XFS_AG_RESV_METADATA:
	131	case XFS_AG_RESV_AGFL:
	132	len -= xfs_perag_resv(pag, type)->ar_reserved;
	133	break;
	134	case XFS_AG_RESV_NONE:
	135	/* empty */
	136	break;
	137	default:
	138	ASSERT(0);
	139	}
	140
	141	trace_xfs_ag_resv_needed(pag, type, len);
	142
	143	return len;
	144	}
	145
	146	/* Clean out a reservation */
	147	static int
	148	__xfs_ag_resv_free(
	149	struct xfs_perag *pag,
	150	enum xfs_ag_resv_type type)
	151	{
	152	struct xfs_ag_resv *resv;
	153	xfs_extlen_t oldresv;
	154	int error;
	155
	156	trace_xfs_ag_resv_free(pag, type, 0);
	157
	158	resv = xfs_perag_resv(pag, type);
	159	pag->pag_mount->m_ag_max_usable += resv->ar_asked;
	160	/*
	161	* AGFL blocks are always considered "free", so whatever
	162	* was reserved at mount time must be given back at umount.
	163	*/
	164	if (type == XFS_AG_RESV_AGFL)
	165	oldresv = resv->ar_orig_reserved;
	166	else
	167	oldresv = resv->ar_reserved;
	168	error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
	169	resv->ar_reserved = 0;
	170	resv->ar_asked = 0;
	171
	172	if (error)
	173	trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
	174	error, _RET_IP_);
	175	return error;
	176	}
	177
	178	/* Free a per-AG reservation. */
179	int
180	xfs_ag_resv_free(
181	struct xfs_perag *pag)
182	{
183	int error;
184	int err2;
185
186	error = __xfs_ag_resv_free(pag, XFS_AG_RESV_AGFL);
187	err2 = __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
188	if (err2 && !error)
189	error = err2;
190	return error;
191	}
192
193	static int
194	__xfs_ag_resv_init(
195	struct xfs_perag *pag,
196	enum xfs_ag_resv_type type,
197	xfs_extlen_t ask,
198	xfs_extlen_t used)
199	{
200	struct xfs_mount *mp = pag->pag_mount;
201	struct xfs_ag_resv *resv;
202	int error;
203
204	resv = xfs_perag_resv(pag, type);
205	if (used > ask)
206	ask = used;
207	resv->ar_asked = ask;
208	resv->ar_reserved = resv->ar_orig_reserved = ask - used;
209	mp->m_ag_max_usable -= ask;
210
211	trace_xfs_ag_resv_init(pag, type, ask);
212
213	error = xfs_mod_fdblocks(mp, -(int64_t)resv->ar_reserved, true);
214	if (error)
215	trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
216	error, _RET_IP_);
217
218	return error;
219	}
220
221	/* Create a per-AG block reservation. */
222	int
223	xfs_ag_resv_init(
224	struct xfs_perag *pag)
225	{
226	xfs_extlen_t ask;
227	xfs_extlen_t used;
228	int error = 0;
229
230	/* Create the metadata reservation. */
231	if (pag->pag_meta_resv.ar_asked == 0) {
232	ask = used = 0;
233
84d69619 DW	234	error = xfs_refcountbt_calc_reserves(pag->pag_mount,
	235	pag->pag_agno, &ask, &used);
	236	if (error)
	237	goto out;
	238
3fd129b6 DW	239	error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
	240	ask, used);
	241	if (error)
	242	goto out;
	243	}
	244
	245	/* Create the AGFL metadata reservation */
	246	if (pag->pag_agfl_resv.ar_asked == 0) {
	247	ask = used = 0;
	248
84d69619 DW	249	error = xfs_rmapbt_calc_reserves(pag->pag_mount, pag->pag_agno,
	250	&ask, &used);
	251	if (error)
	252	goto out;
	253
3fd129b6 DW	254	error = __xfs_ag_resv_init(pag, XFS_AG_RESV_AGFL, ask, used);
	255	if (error)
	256	goto out;
	257	}
	258
20e73b00 DW	259	ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
	260	xfs_perag_resv(pag, XFS_AG_RESV_AGFL)->ar_reserved <=
	261	pag->pagf_freeblks + pag->pagf_flcount);
3fd129b6 DW	262	out:
	263	return error;
	264	}
	265
	266	/* Allocate a block from the reservation. */
	267	void
	268	xfs_ag_resv_alloc_extent(
	269	struct xfs_perag *pag,
	270	enum xfs_ag_resv_type type,
	271	struct xfs_alloc_arg *args)
	272	{
	273	struct xfs_ag_resv *resv;
	274	xfs_extlen_t len;
	275	uint field;
	276
	277	trace_xfs_ag_resv_alloc_extent(pag, type, args->len);
	278
	279	switch (type) {
	280	case XFS_AG_RESV_METADATA:
	281	case XFS_AG_RESV_AGFL:
	282	resv = xfs_perag_resv(pag, type);
	283	break;
	284	default:
	285	ASSERT(0);
	286	/* fall through */
	287	case XFS_AG_RESV_NONE:
	288	field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
	289	XFS_TRANS_SB_FDBLOCKS;
	290	xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
	291	return;
	292	}
	293
	294	len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
	295	resv->ar_reserved -= len;
	296	if (type == XFS_AG_RESV_AGFL)
	297	return;
	298	/* Allocations of reserved blocks only need on-disk sb updates... */
	299	xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
	300	/* ...but non-reserved blocks need in-core and on-disk updates. */
	301	if (args->len > len)
	302	xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
	303	-((int64_t)args->len - len));
	304	}
	305
	306	/* Free a block to the reservation. */
	307	void
	308	xfs_ag_resv_free_extent(
	309	struct xfs_perag *pag,
	310	enum xfs_ag_resv_type type,
	311	struct xfs_trans *tp,
	312	xfs_extlen_t len)
	313	{
	314	xfs_extlen_t leftover;
	315	struct xfs_ag_resv *resv;
	316
	317	trace_xfs_ag_resv_free_extent(pag, type, len);
	318
	319	switch (type) {
	320	case XFS_AG_RESV_METADATA:
	321	case XFS_AG_RESV_AGFL:
	322	resv = xfs_perag_resv(pag, type);
	323	break;
	324	default:
	325	ASSERT(0);
326	/* fall through */
327	case XFS_AG_RESV_NONE:
328	xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
329	return;
330	}
331
332	leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
333	resv->ar_reserved += leftover;
334	if (type == XFS_AG_RESV_AGFL)
335	return;
336	/* Freeing into the reserved pool only requires on-disk update... */
337	xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
338	/* ...but freeing beyond that requires in-core and on-disk update. */
339	if (len > leftover)
340	xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
341	}