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diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
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+/*
+ * 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"
+
+/*
+ * 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 avail < orig / 10 || avail < XFS_BTREE_MAXLEVELS;
+}
+
+/*
+ * 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_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_ag_resv_init(pag, XFS_AG_RESV_AGFL, ask, used);
+ if (error)
+ goto out;
+ }
+
+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);
+}