// SPDX-License-Identifier: GPL-2.0+
/*
* Copyright (C) 2016 Oracle. All Rights Reserved.
* Author: Darrick J. Wong <[email protected]>
*/
#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_mount.h"
#include "xfs_alloc.h"
#include "xfs_errortag.h"
#include "xfs_error.h"
#include "xfs_trace.h"
#include "xfs_trans.h"
#include "xfs_rmap_btree.h"
#include "xfs_btree.h"
#include "xfs_refcount_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_ag.h"
#include "xfs_ag_resv.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_rmapbt_resv.ar_reserved;
orig = pag->pag_meta_resv.ar_asked;
break;
case XFS_AG_RESV_RMAPBT:
avail = pag->pagf_freeblks + pag->pagf_flcount -
pag->pag_meta_resv.ar_reserved;
orig = pag->pag_rmapbt_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 < pag->pag_mount->m_agbtree_maxlevels,
pag->pag_mount, XFS_ERRTAG_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_rmapbt_resv.ar_reserved;
switch (type) {
case XFS_AG_RESV_METADATA:
case XFS_AG_RESV_RMAPBT:
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 void
__xfs_ag_resv_free(
struct xfs_perag *pag,
enum xfs_ag_resv_type type)
{
struct xfs_ag_resv *resv;
xfs_extlen_t oldresv;
trace_xfs_ag_resv_free(pag, type, 0);
resv = xfs_perag_resv(pag, type);
if (pag->pag_agno == 0)
pag->pag_mount->m_ag_max_usable += resv->ar_asked;
/*
* RMAPBT blocks come from the AGFL and AGFL blocks are always
* considered "free", so whatever was reserved at mount time must be
* given back at umount.
*/
if (type == XFS_AG_RESV_RMAPBT)
oldresv = resv->ar_orig_reserved;
else
oldresv = resv->ar_reserved;
xfs_add_fdblocks(pag->pag_mount, oldresv);
resv->ar_reserved = 0;
resv->ar_asked = 0;
resv->ar_orig_reserved = 0;
}
/* Free a per-AG reservation. */
void
xfs_ag_resv_free(
struct xfs_perag *pag)
{
__xfs_ag_resv_free(pag, XFS_AG_RESV_RMAPBT);
__xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
}
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;
xfs_extlen_t hidden_space;
if (used > ask)
ask = used;
switch (type) {
case XFS_AG_RESV_RMAPBT:
/*
* Space taken by the rmapbt is not subtracted from fdblocks
* because the rmapbt lives in the free space. Here we must
* subtract the entire reservation from fdblocks so that we
* always have blocks available for rmapbt expansion.
*/
hidden_space = ask;
break;
case XFS_AG_RESV_METADATA:
/*
* Space taken by all other metadata btrees are accounted
* on-disk as used space. We therefore only hide the space
* that is reserved but not used by the trees.
*/
hidden_space = ask - used;
break;
default:
ASSERT(0);
return -EINVAL;
}
if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_AG_RESV_FAIL))
error = -ENOSPC;
else
error = xfs_dec_fdblocks(mp, hidden_space, true);
if (error) {
trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
error, _RET_IP_);
xfs_warn(mp,
"Per-AG reservation for AG %u failed. Filesystem may run out of space.",
pag->pag_agno);
return error;
}
/*
* Reduce the maximum per-AG allocation length by however much we're
* trying to reserve for an AG. Since this is a filesystem-wide
* counter, we only make the adjustment for AG 0. This assumes that
* there aren't any AGs hungrier for per-AG reservation than AG 0.
*/
if (pag->pag_agno == 0)
mp->m_ag_max_usable -= ask;
resv = xfs_perag_resv(pag, type);
resv->ar_asked = ask;
resv->ar_orig_reserved = hidden_space;
resv->ar_reserved = ask - used;
trace_xfs_ag_resv_init(pag, type, ask);
return 0;
}
/* Create a per-AG block reservation. */
int
xfs_ag_resv_init(
struct xfs_perag *pag,
struct xfs_trans *tp)
{
struct xfs_mount *mp = pag->pag_mount;
xfs_extlen_t ask;
xfs_extlen_t used;
int error = 0, error2;
bool has_resv = false;
/* Create the metadata reservation. */
if (pag->pag_meta_resv.ar_asked == 0) {
ask = used = 0;
error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask, &used);
if (error)
goto out;
error = xfs_finobt_calc_reserves(pag, tp, &ask, &used);
if (error)
goto out;
error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
ask, used);
if (error) {
/*
* Because we didn't have per-AG reservations when the
* finobt feature was added we might not be able to
* reserve all needed blocks. Warn and fall back to the
* old and potentially buggy code in that case, but
* ensure we do have the reservation for the refcountbt.
*/
ask = used = 0;
mp->m_finobt_nores = true;
error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask,
&used);
if (error)
goto out;
error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
ask, used);
if (error)
goto out;
}
if (ask)
has_resv = true;
}
/* Create the RMAPBT metadata reservation */
if (pag->pag_rmapbt_resv.ar_asked == 0) {
ask = used = 0;
error = xfs_rmapbt_calc_reserves(mp, tp, pag, &ask, &used);
if (error)
goto out;
error = __xfs_ag_resv_init(pag, XFS_AG_RESV_RMAPBT, ask, used);
if (error)
goto out;
if (ask)
has_resv = true;
}
out:
/*
* Initialize the pagf if we have at least one active reservation on the
* AG. This may have occurred already via reservation calculation, but
* fall back to an explicit init to ensure the in-core allocbt usage
* counters are initialized as soon as possible. This is important
* because filesystems with large perag reservations are susceptible to
* free space reservation problems that the allocbt counter is used to
* address.
*/
if (has_resv) {
error2 = xfs_alloc_read_agf(pag, tp, 0, NULL);
if (error2)
return error2;
/*
* If there isn't enough space in the AG to satisfy the
* reservation, let the caller know that there wasn't enough
* space. Callers are responsible for deciding what to do
* next, since (in theory) we can stumble along with
* insufficient reservation if data blocks are being freed to
* replenish the AG's free space.
*/
if (!error &&
xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved >
pag->pagf_freeblks + pag->pagf_flcount)
error = -ENOSPC;
}
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_AGFL:
return;
case XFS_AG_RESV_METADATA:
case XFS_AG_RESV_RMAPBT:
resv = xfs_perag_resv(pag, type);
break;
default:
ASSERT(0);
fallthrough;
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_RMAPBT)
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_AGFL:
return;
case XFS_AG_RESV_METADATA:
case XFS_AG_RESV_RMAPBT:
resv = xfs_perag_resv(pag, type);
break;
default:
ASSERT(0);
fallthrough;
case XFS_AG_RESV_NONE:
xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
fallthrough;
case XFS_AG_RESV_IGNORE:
return;
}
leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
resv->ar_reserved += leftover;
if (type == XFS_AG_RESV_RMAPBT)
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);
}
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