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Diffstat (limited to 'fs/xfs/xfs_log_priv.h')
| -rw-r--r-- | fs/xfs/xfs_log_priv.h | 712 |
1 files changed, 712 insertions, 0 deletions
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h new file mode 100644 index 0000000000..fa3ad1d7b3 --- /dev/null +++ b/fs/xfs/xfs_log_priv.h @@ -0,0 +1,712 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc. + * All Rights Reserved. + */ +#ifndef __XFS_LOG_PRIV_H__ +#define __XFS_LOG_PRIV_H__ + +#include "xfs_extent_busy.h" /* for struct xfs_busy_extents */ + +struct xfs_buf; +struct xlog; +struct xlog_ticket; +struct xfs_mount; + +/* + * get client id from packed copy. + * + * this hack is here because the xlog_pack code copies four bytes + * of xlog_op_header containing the fields oh_clientid, oh_flags + * and oh_res2 into the packed copy. + * + * later on this four byte chunk is treated as an int and the + * client id is pulled out. + * + * this has endian issues, of course. + */ +static inline uint xlog_get_client_id(__be32 i) +{ + return be32_to_cpu(i) >> 24; +} + +/* + * In core log state + */ +enum xlog_iclog_state { + XLOG_STATE_ACTIVE, /* Current IC log being written to */ + XLOG_STATE_WANT_SYNC, /* Want to sync this iclog; no more writes */ + XLOG_STATE_SYNCING, /* This IC log is syncing */ + XLOG_STATE_DONE_SYNC, /* Done syncing to disk */ + XLOG_STATE_CALLBACK, /* Callback functions now */ + XLOG_STATE_DIRTY, /* Dirty IC log, not ready for ACTIVE status */ +}; + +#define XLOG_STATE_STRINGS \ + { XLOG_STATE_ACTIVE, "XLOG_STATE_ACTIVE" }, \ + { XLOG_STATE_WANT_SYNC, "XLOG_STATE_WANT_SYNC" }, \ + { XLOG_STATE_SYNCING, "XLOG_STATE_SYNCING" }, \ + { XLOG_STATE_DONE_SYNC, "XLOG_STATE_DONE_SYNC" }, \ + { XLOG_STATE_CALLBACK, "XLOG_STATE_CALLBACK" }, \ + { XLOG_STATE_DIRTY, "XLOG_STATE_DIRTY" } + +/* + * In core log flags + */ +#define XLOG_ICL_NEED_FLUSH (1u << 0) /* iclog needs REQ_PREFLUSH */ +#define XLOG_ICL_NEED_FUA (1u << 1) /* iclog needs REQ_FUA */ + +#define XLOG_ICL_STRINGS \ + { XLOG_ICL_NEED_FLUSH, "XLOG_ICL_NEED_FLUSH" }, \ + { XLOG_ICL_NEED_FUA, "XLOG_ICL_NEED_FUA" } + + +/* + * Log ticket flags + */ +#define XLOG_TIC_PERM_RESERV (1u << 0) /* permanent reservation */ + +#define XLOG_TIC_FLAGS \ + { XLOG_TIC_PERM_RESERV, "XLOG_TIC_PERM_RESERV" } + +/* + * Below are states for covering allocation transactions. + * By covering, we mean changing the h_tail_lsn in the last on-disk + * log write such that no allocation transactions will be re-done during + * recovery after a system crash. Recovery starts at the last on-disk + * log write. + * + * These states are used to insert dummy log entries to cover + * space allocation transactions which can undo non-transactional changes + * after a crash. Writes to a file with space + * already allocated do not result in any transactions. Allocations + * might include space beyond the EOF. So if we just push the EOF a + * little, the last transaction for the file could contain the wrong + * size. If there is no file system activity, after an allocation + * transaction, and the system crashes, the allocation transaction + * will get replayed and the file will be truncated. This could + * be hours/days/... after the allocation occurred. + * + * The fix for this is to do two dummy transactions when the + * system is idle. We need two dummy transaction because the h_tail_lsn + * in the log record header needs to point beyond the last possible + * non-dummy transaction. The first dummy changes the h_tail_lsn to + * the first transaction before the dummy. The second dummy causes + * h_tail_lsn to point to the first dummy. Recovery starts at h_tail_lsn. + * + * These dummy transactions get committed when everything + * is idle (after there has been some activity). + * + * There are 5 states used to control this. + * + * IDLE -- no logging has been done on the file system or + * we are done covering previous transactions. + * NEED -- logging has occurred and we need a dummy transaction + * when the log becomes idle. + * DONE -- we were in the NEED state and have committed a dummy + * transaction. + * NEED2 -- we detected that a dummy transaction has gone to the + * on disk log with no other transactions. + * DONE2 -- we committed a dummy transaction when in the NEED2 state. + * + * There are two places where we switch states: + * + * 1.) In xfs_sync, when we detect an idle log and are in NEED or NEED2. + * We commit the dummy transaction and switch to DONE or DONE2, + * respectively. In all other states, we don't do anything. + * + * 2.) When we finish writing the on-disk log (xlog_state_clean_log). + * + * No matter what state we are in, if this isn't the dummy + * transaction going out, the next state is NEED. + * So, if we aren't in the DONE or DONE2 states, the next state + * is NEED. We can't be finishing a write of the dummy record + * unless it was committed and the state switched to DONE or DONE2. + * + * If we are in the DONE state and this was a write of the + * dummy transaction, we move to NEED2. + * + * If we are in the DONE2 state and this was a write of the + * dummy transaction, we move to IDLE. + * + * + * Writing only one dummy transaction can get appended to + * one file space allocation. When this happens, the log recovery + * code replays the space allocation and a file could be truncated. + * This is why we have the NEED2 and DONE2 states before going idle. + */ + +#define XLOG_STATE_COVER_IDLE 0 +#define XLOG_STATE_COVER_NEED 1 +#define XLOG_STATE_COVER_DONE 2 +#define XLOG_STATE_COVER_NEED2 3 +#define XLOG_STATE_COVER_DONE2 4 + +#define XLOG_COVER_OPS 5 + +typedef struct xlog_ticket { + struct list_head t_queue; /* reserve/write queue */ + struct task_struct *t_task; /* task that owns this ticket */ + xlog_tid_t t_tid; /* transaction identifier */ + atomic_t t_ref; /* ticket reference count */ + int t_curr_res; /* current reservation */ + int t_unit_res; /* unit reservation */ + char t_ocnt; /* original unit count */ + char t_cnt; /* current unit count */ + uint8_t t_flags; /* properties of reservation */ + int t_iclog_hdrs; /* iclog hdrs in t_curr_res */ +} xlog_ticket_t; + +/* + * - A log record header is 512 bytes. There is plenty of room to grow the + * xlog_rec_header_t into the reserved space. + * - ic_data follows, so a write to disk can start at the beginning of + * the iclog. + * - ic_forcewait is used to implement synchronous forcing of the iclog to disk. + * - ic_next is the pointer to the next iclog in the ring. + * - ic_log is a pointer back to the global log structure. + * - ic_size is the full size of the log buffer, minus the cycle headers. + * - ic_offset is the current number of bytes written to in this iclog. + * - ic_refcnt is bumped when someone is writing to the log. + * - ic_state is the state of the iclog. + * + * Because of cacheline contention on large machines, we need to separate + * various resources onto different cachelines. To start with, make the + * structure cacheline aligned. The following fields can be contended on + * by independent processes: + * + * - ic_callbacks + * - ic_refcnt + * - fields protected by the global l_icloglock + * + * so we need to ensure that these fields are located in separate cachelines. + * We'll put all the read-only and l_icloglock fields in the first cacheline, + * and move everything else out to subsequent cachelines. + */ +typedef struct xlog_in_core { + wait_queue_head_t ic_force_wait; + wait_queue_head_t ic_write_wait; + struct xlog_in_core *ic_next; + struct xlog_in_core *ic_prev; + struct xlog *ic_log; + u32 ic_size; + u32 ic_offset; + enum xlog_iclog_state ic_state; + unsigned int ic_flags; + void *ic_datap; /* pointer to iclog data */ + struct list_head ic_callbacks; + + /* reference counts need their own cacheline */ + atomic_t ic_refcnt ____cacheline_aligned_in_smp; + xlog_in_core_2_t *ic_data; +#define ic_header ic_data->hic_header +#ifdef DEBUG + bool ic_fail_crc : 1; +#endif + struct semaphore ic_sema; + struct work_struct ic_end_io_work; + struct bio ic_bio; + struct bio_vec ic_bvec[]; +} xlog_in_core_t; + +/* + * The CIL context is used to aggregate per-transaction details as well be + * passed to the iclog for checkpoint post-commit processing. After being + * passed to the iclog, another context needs to be allocated for tracking the + * next set of transactions to be aggregated into a checkpoint. + */ +struct xfs_cil; + +struct xfs_cil_ctx { + struct xfs_cil *cil; + xfs_csn_t sequence; /* chkpt sequence # */ + xfs_lsn_t start_lsn; /* first LSN of chkpt commit */ + xfs_lsn_t commit_lsn; /* chkpt commit record lsn */ + struct xlog_in_core *commit_iclog; + struct xlog_ticket *ticket; /* chkpt ticket */ + atomic_t space_used; /* aggregate size of regions */ + struct xfs_busy_extents busy_extents; + struct list_head log_items; /* log items in chkpt */ + struct list_head lv_chain; /* logvecs being pushed */ + struct list_head iclog_entry; + struct list_head committing; /* ctx committing list */ + struct work_struct push_work; + atomic_t order_id; + + /* + * CPUs that could have added items to the percpu CIL data. Access is + * coordinated with xc_ctx_lock. + */ + struct cpumask cil_pcpmask; +}; + +/* + * Per-cpu CIL tracking items + */ +struct xlog_cil_pcp { + int32_t space_used; + uint32_t space_reserved; + struct list_head busy_extents; + struct list_head log_items; +}; + +/* + * Committed Item List structure + * + * This structure is used to track log items that have been committed but not + * yet written into the log. It is used only when the delayed logging mount + * option is enabled. + * + * This structure tracks the list of committing checkpoint contexts so + * we can avoid the problem of having to hold out new transactions during a + * flush until we have a the commit record LSN of the checkpoint. We can + * traverse the list of committing contexts in xlog_cil_push_lsn() to find a + * sequence match and extract the commit LSN directly from there. If the + * checkpoint is still in the process of committing, we can block waiting for + * the commit LSN to be determined as well. This should make synchronous + * operations almost as efficient as the old logging methods. + */ +struct xfs_cil { + struct xlog *xc_log; + unsigned long xc_flags; + atomic_t xc_iclog_hdrs; + struct workqueue_struct *xc_push_wq; + + struct rw_semaphore xc_ctx_lock ____cacheline_aligned_in_smp; + struct xfs_cil_ctx *xc_ctx; + + spinlock_t xc_push_lock ____cacheline_aligned_in_smp; + xfs_csn_t xc_push_seq; + bool xc_push_commit_stable; + struct list_head xc_committing; + wait_queue_head_t xc_commit_wait; + wait_queue_head_t xc_start_wait; + xfs_csn_t xc_current_sequence; + wait_queue_head_t xc_push_wait; /* background push throttle */ + + void __percpu *xc_pcp; /* percpu CIL structures */ +} ____cacheline_aligned_in_smp; + +/* xc_flags bit values */ +#define XLOG_CIL_EMPTY 1 +#define XLOG_CIL_PCP_SPACE 2 + +/* + * The amount of log space we allow the CIL to aggregate is difficult to size. + * Whatever we choose, we have to make sure we can get a reservation for the + * log space effectively, that it is large enough to capture sufficient + * relogging to reduce log buffer IO significantly, but it is not too large for + * the log or induces too much latency when writing out through the iclogs. We + * track both space consumed and the number of vectors in the checkpoint + * context, so we need to decide which to use for limiting. + * + * Every log buffer we write out during a push needs a header reserved, which + * is at least one sector and more for v2 logs. Hence we need a reservation of + * at least 512 bytes per 32k of log space just for the LR headers. That means + * 16KB of reservation per megabyte of delayed logging space we will consume, + * plus various headers. The number of headers will vary based on the num of + * io vectors, so limiting on a specific number of vectors is going to result + * in transactions of varying size. IOWs, it is more consistent to track and + * limit space consumed in the log rather than by the number of objects being + * logged in order to prevent checkpoint ticket overruns. + * + * Further, use of static reservations through the log grant mechanism is + * problematic. It introduces a lot of complexity (e.g. reserve grant vs write + * grant) and a significant deadlock potential because regranting write space + * can block on log pushes. Hence if we have to regrant log space during a log + * push, we can deadlock. + * + * However, we can avoid this by use of a dynamic "reservation stealing" + * technique during transaction commit whereby unused reservation space in the + * transaction ticket is transferred to the CIL ctx commit ticket to cover the + * space needed by the checkpoint transaction. This means that we never need to + * specifically reserve space for the CIL checkpoint transaction, nor do we + * need to regrant space once the checkpoint completes. This also means the + * checkpoint transaction ticket is specific to the checkpoint context, rather + * than the CIL itself. + * + * With dynamic reservations, we can effectively make up arbitrary limits for + * the checkpoint size so long as they don't violate any other size rules. + * Recovery imposes a rule that no transaction exceed half the log, so we are + * limited by that. Furthermore, the log transaction reservation subsystem + * tries to keep 25% of the log free, so we need to keep below that limit or we + * risk running out of free log space to start any new transactions. + * + * In order to keep background CIL push efficient, we only need to ensure the + * CIL is large enough to maintain sufficient in-memory relogging to avoid + * repeated physical writes of frequently modified metadata. If we allow the CIL + * to grow to a substantial fraction of the log, then we may be pinning hundreds + * of megabytes of metadata in memory until the CIL flushes. This can cause + * issues when we are running low on memory - pinned memory cannot be reclaimed, + * and the CIL consumes a lot of memory. Hence we need to set an upper physical + * size limit for the CIL that limits the maximum amount of memory pinned by the + * CIL but does not limit performance by reducing relogging efficiency + * significantly. + * + * As such, the CIL push threshold ends up being the smaller of two thresholds: + * - a threshold large enough that it allows CIL to be pushed and progress to be + * made without excessive blocking of incoming transaction commits. This is + * defined to be 12.5% of the log space - half the 25% push threshold of the + * AIL. + * - small enough that it doesn't pin excessive amounts of memory but maintains + * close to peak relogging efficiency. This is defined to be 16x the iclog + * buffer window (32MB) as measurements have shown this to be roughly the + * point of diminishing performance increases under highly concurrent + * modification workloads. + * + * To prevent the CIL from overflowing upper commit size bounds, we introduce a + * new threshold at which we block committing transactions until the background + * CIL commit commences and switches to a new context. While this is not a hard + * limit, it forces the process committing a transaction to the CIL to block and + * yeild the CPU, giving the CIL push work a chance to be scheduled and start + * work. This prevents a process running lots of transactions from overfilling + * the CIL because it is not yielding the CPU. We set the blocking limit at + * twice the background push space threshold so we keep in line with the AIL + * push thresholds. + * + * Note: this is not a -hard- limit as blocking is applied after the transaction + * is inserted into the CIL and the push has been triggered. It is largely a + * throttling mechanism that allows the CIL push to be scheduled and run. A hard + * limit will be difficult to implement without introducing global serialisation + * in the CIL commit fast path, and it's not at all clear that we actually need + * such hard limits given the ~7 years we've run without a hard limit before + * finding the first situation where a checkpoint size overflow actually + * occurred. Hence the simple throttle, and an ASSERT check to tell us that + * we've overrun the max size. + */ +#define XLOG_CIL_SPACE_LIMIT(log) \ + min_t(int, (log)->l_logsize >> 3, BBTOB(XLOG_TOTAL_REC_SHIFT(log)) << 4) + +#define XLOG_CIL_BLOCKING_SPACE_LIMIT(log) \ + (XLOG_CIL_SPACE_LIMIT(log) * 2) + +/* + * ticket grant locks, queues and accounting have their own cachlines + * as these are quite hot and can be operated on concurrently. + */ +struct xlog_grant_head { + spinlock_t lock ____cacheline_aligned_in_smp; + struct list_head waiters; + atomic64_t grant; +}; + +/* + * The reservation head lsn is not made up of a cycle number and block number. + * Instead, it uses a cycle number and byte number. Logs don't expect to + * overflow 31 bits worth of byte offset, so using a byte number will mean + * that round off problems won't occur when releasing partial reservations. + */ +struct xlog { + /* The following fields don't need locking */ + struct xfs_mount *l_mp; /* mount point */ + struct xfs_ail *l_ailp; /* AIL log is working with */ + struct xfs_cil *l_cilp; /* CIL log is working with */ + struct xfs_buftarg *l_targ; /* buftarg of log */ + struct workqueue_struct *l_ioend_workqueue; /* for I/O completions */ + struct delayed_work l_work; /* background flush work */ + long l_opstate; /* operational state */ + uint l_quotaoffs_flag; /* XFS_DQ_*, for QUOTAOFFs */ + struct list_head *l_buf_cancel_table; + int l_iclog_hsize; /* size of iclog header */ + int l_iclog_heads; /* # of iclog header sectors */ + uint l_sectBBsize; /* sector size in BBs (2^n) */ + int l_iclog_size; /* size of log in bytes */ + int l_iclog_bufs; /* number of iclog buffers */ + xfs_daddr_t l_logBBstart; /* start block of log */ + int l_logsize; /* size of log in bytes */ + int l_logBBsize; /* size of log in BB chunks */ + + /* The following block of fields are changed while holding icloglock */ + wait_queue_head_t l_flush_wait ____cacheline_aligned_in_smp; + /* waiting for iclog flush */ + int l_covered_state;/* state of "covering disk + * log entries" */ + xlog_in_core_t *l_iclog; /* head log queue */ + spinlock_t l_icloglock; /* grab to change iclog state */ + int l_curr_cycle; /* Cycle number of log writes */ + int l_prev_cycle; /* Cycle number before last + * block increment */ + int l_curr_block; /* current logical log block */ + int l_prev_block; /* previous logical log block */ + + /* + * l_last_sync_lsn and l_tail_lsn are atomics so they can be set and + * read without needing to hold specific locks. To avoid operations + * contending with other hot objects, place each of them on a separate + * cacheline. + */ + /* lsn of last LR on disk */ + atomic64_t l_last_sync_lsn ____cacheline_aligned_in_smp; + /* lsn of 1st LR with unflushed * buffers */ + atomic64_t l_tail_lsn ____cacheline_aligned_in_smp; + + struct xlog_grant_head l_reserve_head; + struct xlog_grant_head l_write_head; + + struct xfs_kobj l_kobj; + + /* log recovery lsn tracking (for buffer submission */ + xfs_lsn_t l_recovery_lsn; + + uint32_t l_iclog_roundoff;/* padding roundoff */ + + /* Users of log incompat features should take a read lock. */ + struct rw_semaphore l_incompat_users; +}; + +/* + * Bits for operational state + */ +#define XLOG_ACTIVE_RECOVERY 0 /* in the middle of recovery */ +#define XLOG_RECOVERY_NEEDED 1 /* log was recovered */ +#define XLOG_IO_ERROR 2 /* log hit an I/O error, and being + shutdown */ +#define XLOG_TAIL_WARN 3 /* log tail verify warning issued */ + +static inline bool +xlog_recovery_needed(struct xlog *log) +{ + return test_bit(XLOG_RECOVERY_NEEDED, &log->l_opstate); +} + +static inline bool +xlog_in_recovery(struct xlog *log) +{ + return test_bit(XLOG_ACTIVE_RECOVERY, &log->l_opstate); +} + +static inline bool +xlog_is_shutdown(struct xlog *log) +{ + return test_bit(XLOG_IO_ERROR, &log->l_opstate); +} + +/* + * Wait until the xlog_force_shutdown() has marked the log as shut down + * so xlog_is_shutdown() will always return true. + */ +static inline void +xlog_shutdown_wait( + struct xlog *log) +{ + wait_var_event(&log->l_opstate, xlog_is_shutdown(log)); +} + +/* common routines */ +extern int +xlog_recover( + struct xlog *log); +extern int +xlog_recover_finish( + struct xlog *log); +extern void +xlog_recover_cancel(struct xlog *); + +extern __le32 xlog_cksum(struct xlog *log, struct xlog_rec_header *rhead, + char *dp, int size); + +extern struct kmem_cache *xfs_log_ticket_cache; +struct xlog_ticket *xlog_ticket_alloc(struct xlog *log, int unit_bytes, + int count, bool permanent); + +void xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket); +void xlog_print_trans(struct xfs_trans *); +int xlog_write(struct xlog *log, struct xfs_cil_ctx *ctx, + struct list_head *lv_chain, struct xlog_ticket *tic, + uint32_t len); +void xfs_log_ticket_ungrant(struct xlog *log, struct xlog_ticket *ticket); +void xfs_log_ticket_regrant(struct xlog *log, struct xlog_ticket *ticket); + +void xlog_state_switch_iclogs(struct xlog *log, struct xlog_in_core *iclog, + int eventual_size); +int xlog_state_release_iclog(struct xlog *log, struct xlog_in_core *iclog, + struct xlog_ticket *ticket); + +/* + * When we crack an atomic LSN, we sample it first so that the value will not + * change while we are cracking it into the component values. This means we + * will always get consistent component values to work from. This should always + * be used to sample and crack LSNs that are stored and updated in atomic + * variables. + */ +static inline void +xlog_crack_atomic_lsn(atomic64_t *lsn, uint *cycle, uint *block) +{ + xfs_lsn_t val = atomic64_read(lsn); + + *cycle = CYCLE_LSN(val); + *block = BLOCK_LSN(val); +} + +/* + * Calculate and assign a value to an atomic LSN variable from component pieces. + */ +static inline void +xlog_assign_atomic_lsn(atomic64_t *lsn, uint cycle, uint block) +{ + atomic64_set(lsn, xlog_assign_lsn(cycle, block)); +} + +/* + * When we crack the grant head, we sample it first so that the value will not + * change while we are cracking it into the component values. This means we + * will always get consistent component values to work from. + */ +static inline void +xlog_crack_grant_head_val(int64_t val, int *cycle, int *space) +{ + *cycle = val >> 32; + *space = val & 0xffffffff; +} + +static inline void +xlog_crack_grant_head(atomic64_t *head, int *cycle, int *space) +{ + xlog_crack_grant_head_val(atomic64_read(head), cycle, space); +} + +static inline int64_t +xlog_assign_grant_head_val(int cycle, int space) +{ + return ((int64_t)cycle << 32) | space; +} + +static inline void +xlog_assign_grant_head(atomic64_t *head, int cycle, int space) +{ + atomic64_set(head, xlog_assign_grant_head_val(cycle, space)); +} + +/* + * Committed Item List interfaces + */ +int xlog_cil_init(struct xlog *log); +void xlog_cil_init_post_recovery(struct xlog *log); +void xlog_cil_destroy(struct xlog *log); +bool xlog_cil_empty(struct xlog *log); +void xlog_cil_commit(struct xlog *log, struct xfs_trans *tp, + xfs_csn_t *commit_seq, bool regrant); +void xlog_cil_set_ctx_write_state(struct xfs_cil_ctx *ctx, + struct xlog_in_core *iclog); + + +/* + * CIL force routines + */ +void xlog_cil_flush(struct xlog *log); +xfs_lsn_t xlog_cil_force_seq(struct xlog *log, xfs_csn_t sequence); + +static inline void +xlog_cil_force(struct xlog *log) +{ + xlog_cil_force_seq(log, log->l_cilp->xc_current_sequence); +} + +/* + * Wrapper function for waiting on a wait queue serialised against wakeups + * by a spinlock. This matches the semantics of all the wait queues used in the + * log code. + */ +static inline void +xlog_wait( + struct wait_queue_head *wq, + struct spinlock *lock) + __releases(lock) +{ + DECLARE_WAITQUEUE(wait, current); + + add_wait_queue_exclusive(wq, &wait); + __set_current_state(TASK_UNINTERRUPTIBLE); + spin_unlock(lock); + schedule(); + remove_wait_queue(wq, &wait); +} + +int xlog_wait_on_iclog(struct xlog_in_core *iclog); + +/* + * The LSN is valid so long as it is behind the current LSN. If it isn't, this + * means that the next log record that includes this metadata could have a + * smaller LSN. In turn, this means that the modification in the log would not + * replay. + */ +static inline bool +xlog_valid_lsn( + struct xlog *log, + xfs_lsn_t lsn) +{ + int cur_cycle; + int cur_block; + bool valid = true; + + /* + * First, sample the current lsn without locking to avoid added + * contention from metadata I/O. The current cycle and block are updated + * (in xlog_state_switch_iclogs()) and read here in a particular order + * to avoid false negatives (e.g., thinking the metadata LSN is valid + * when it is not). + * + * The current block is always rewound before the cycle is bumped in + * xlog_state_switch_iclogs() to ensure the current LSN is never seen in + * a transiently forward state. Instead, we can see the LSN in a + * transiently behind state if we happen to race with a cycle wrap. + */ + cur_cycle = READ_ONCE(log->l_curr_cycle); + smp_rmb(); + cur_block = READ_ONCE(log->l_curr_block); + + if ((CYCLE_LSN(lsn) > cur_cycle) || + (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block)) { + /* + * If the metadata LSN appears invalid, it's possible the check + * above raced with a wrap to the next log cycle. Grab the lock + * to check for sure. + */ + spin_lock(&log->l_icloglock); + cur_cycle = log->l_curr_cycle; + cur_block = log->l_curr_block; + spin_unlock(&log->l_icloglock); + + if ((CYCLE_LSN(lsn) > cur_cycle) || + (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block)) + valid = false; + } + + return valid; +} + +/* + * Log vector and shadow buffers can be large, so we need to use kvmalloc() here + * to ensure success. Unfortunately, kvmalloc() only allows GFP_KERNEL contexts + * to fall back to vmalloc, so we can't actually do anything useful with gfp + * flags to control the kmalloc() behaviour within kvmalloc(). Hence kmalloc() + * will do direct reclaim and compaction in the slow path, both of which are + * horrendously expensive. We just want kmalloc to fail fast and fall back to + * vmalloc if it can't get somethign straight away from the free lists or + * buddy allocator. Hence we have to open code kvmalloc outselves here. + * + * This assumes that the caller uses memalloc_nofs_save task context here, so + * despite the use of GFP_KERNEL here, we are going to be doing GFP_NOFS + * allocations. This is actually the only way to make vmalloc() do GFP_NOFS + * allocations, so lets just all pretend this is a GFP_KERNEL context + * operation.... + */ +static inline void * +xlog_kvmalloc( + size_t buf_size) +{ + gfp_t flags = GFP_KERNEL; + void *p; + + flags &= ~__GFP_DIRECT_RECLAIM; + flags |= __GFP_NOWARN | __GFP_NORETRY; + do { + p = kmalloc(buf_size, flags); + if (!p) + p = vmalloc(buf_size); + } while (!p); + + return p; +} + +#endif /* __XFS_LOG_PRIV_H__ */ |