kernel-ark/fs/xfs/xfs_log_cil.c
Dave Chinner b1c5ebb213 xfs: allocate log vector buffers outside CIL context lock
One of the problems we currently have with delayed logging is that
under serious memory pressure we can deadlock memory reclaim. THis
occurs when memory reclaim (such as run by kswapd) is reclaiming XFS
inodes and issues a log force to unpin inodes that are dirty in the
CIL.

The CIL is pushed, but this will only occur once it gets the CIL
context lock to ensure that all committing transactions are complete
and no new transactions start being committed to the CIL while the
push switches to a new context.

The deadlock occurs when the CIL context lock is held by a
committing process that is doing memory allocation for log vector
buffers, and that allocation is then blocked on memory reclaim
making progress. Memory reclaim, however, is blocked waiting for
a log force to make progress, and so we effectively deadlock at this
point.

To solve this problem, we have to move the CIL log vector buffer
allocation outside of the context lock so that memory reclaim can
always make progress when it needs to force the log. The problem
with doing this is that a CIL push can take place while we are
determining if we need to allocate a new log vector buffer for
an item and hence the current log vector may go away without
warning. That means we canot rely on the existing log vector being
present when we finally grab the context lock and so we must have a
replacement buffer ready to go at all times.

To ensure this, introduce a "shadow log vector" buffer that is
always guaranteed to be present when we gain the CIL context lock
and format the item. This shadow buffer may or may not be used
during the formatting, but if the log item does not have an existing
log vector buffer or that buffer is too small for the new
modifications, we swap it for the new shadow buffer and format
the modifications into that new log vector buffer.

The result of this is that for any object we modify more than once
in a given CIL checkpoint, we double the memory required
to track dirty regions in the log. For single modifications then
we consume the shadow log vectorwe allocate on commit, and that gets
consumed by the checkpoint. However, if we make multiple
modifications, then the second transaction commit will allocate a
shadow log vector and hence we will end up with double the memory
usage as only one of the log vectors is consumed by the CIL
checkpoint. The remaining shadow vector will be freed when th elog
item is freed.

This can probably be optimised in future - access to the shadow log
vector is serialised by the object lock (as opposited to the active
log vector, which is controlled by the CIL context lock) and so we
can probably free shadow log vector from some objects when the log
item is marked clean on removal from the AIL.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
2016-07-22 09:52:35 +10:00

1130 lines
35 KiB
C

/*
* Copyright (c) 2010 Red Hat, Inc. All Rights Reserved.
*
* 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.
*
* 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_format.h"
#include "xfs_log_format.h"
#include "xfs_shared.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_error.h"
#include "xfs_alloc.h"
#include "xfs_extent_busy.h"
#include "xfs_discard.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_log.h"
#include "xfs_log_priv.h"
/*
* Allocate a new ticket. Failing to get a new ticket makes it really hard to
* recover, so we don't allow failure here. Also, we allocate in a context that
* we don't want to be issuing transactions from, so we need to tell the
* allocation code this as well.
*
* We don't reserve any space for the ticket - we are going to steal whatever
* space we require from transactions as they commit. To ensure we reserve all
* the space required, we need to set the current reservation of the ticket to
* zero so that we know to steal the initial transaction overhead from the
* first transaction commit.
*/
static struct xlog_ticket *
xlog_cil_ticket_alloc(
struct xlog *log)
{
struct xlog_ticket *tic;
tic = xlog_ticket_alloc(log, 0, 1, XFS_TRANSACTION, 0,
KM_SLEEP|KM_NOFS);
/*
* set the current reservation to zero so we know to steal the basic
* transaction overhead reservation from the first transaction commit.
*/
tic->t_curr_res = 0;
return tic;
}
/*
* After the first stage of log recovery is done, we know where the head and
* tail of the log are. We need this log initialisation done before we can
* initialise the first CIL checkpoint context.
*
* Here we allocate a log ticket to track space usage during a CIL push. This
* ticket is passed to xlog_write() directly so that we don't slowly leak log
* space by failing to account for space used by log headers and additional
* region headers for split regions.
*/
void
xlog_cil_init_post_recovery(
struct xlog *log)
{
log->l_cilp->xc_ctx->ticket = xlog_cil_ticket_alloc(log);
log->l_cilp->xc_ctx->sequence = 1;
}
static inline int
xlog_cil_iovec_space(
uint niovecs)
{
return round_up((sizeof(struct xfs_log_vec) +
niovecs * sizeof(struct xfs_log_iovec)),
sizeof(uint64_t));
}
/*
* Allocate or pin log vector buffers for CIL insertion.
*
* The CIL currently uses disposable buffers for copying a snapshot of the
* modified items into the log during a push. The biggest problem with this is
* the requirement to allocate the disposable buffer during the commit if:
* a) does not exist; or
* b) it is too small
*
* If we do this allocation within xlog_cil_insert_format_items(), it is done
* under the xc_ctx_lock, which means that a CIL push cannot occur during
* the memory allocation. This means that we have a potential deadlock situation
* under low memory conditions when we have lots of dirty metadata pinned in
* the CIL and we need a CIL commit to occur to free memory.
*
* To avoid this, we need to move the memory allocation outside the
* xc_ctx_lock, but because the log vector buffers are disposable, that opens
* up a TOCTOU race condition w.r.t. the CIL committing and removing the log
* vector buffers between the check and the formatting of the item into the
* log vector buffer within the xc_ctx_lock.
*
* Because the log vector buffer needs to be unchanged during the CIL push
* process, we cannot share the buffer between the transaction commit (which
* modifies the buffer) and the CIL push context that is writing the changes
* into the log. This means skipping preallocation of buffer space is
* unreliable, but we most definitely do not want to be allocating and freeing
* buffers unnecessarily during commits when overwrites can be done safely.
*
* The simplest solution to this problem is to allocate a shadow buffer when a
* log item is committed for the second time, and then to only use this buffer
* if necessary. The buffer can remain attached to the log item until such time
* it is needed, and this is the buffer that is reallocated to match the size of
* the incoming modification. Then during the formatting of the item we can swap
* the active buffer with the new one if we can't reuse the existing buffer. We
* don't free the old buffer as it may be reused on the next modification if
* it's size is right, otherwise we'll free and reallocate it at that point.
*
* This function builds a vector for the changes in each log item in the
* transaction. It then works out the length of the buffer needed for each log
* item, allocates them and attaches the vector to the log item in preparation
* for the formatting step which occurs under the xc_ctx_lock.
*
* While this means the memory footprint goes up, it avoids the repeated
* alloc/free pattern that repeated modifications of an item would otherwise
* cause, and hence minimises the CPU overhead of such behaviour.
*/
static void
xlog_cil_alloc_shadow_bufs(
struct xlog *log,
struct xfs_trans *tp)
{
struct xfs_log_item_desc *lidp;
list_for_each_entry(lidp, &tp->t_items, lid_trans) {
struct xfs_log_item *lip = lidp->lid_item;
struct xfs_log_vec *lv;
int niovecs = 0;
int nbytes = 0;
int buf_size;
bool ordered = false;
/* Skip items which aren't dirty in this transaction. */
if (!(lidp->lid_flags & XFS_LID_DIRTY))
continue;
/* get number of vecs and size of data to be stored */
lip->li_ops->iop_size(lip, &niovecs, &nbytes);
/*
* Ordered items need to be tracked but we do not wish to write
* them. We need a logvec to track the object, but we do not
* need an iovec or buffer to be allocated for copying data.
*/
if (niovecs == XFS_LOG_VEC_ORDERED) {
ordered = true;
niovecs = 0;
nbytes = 0;
}
/*
* We 64-bit align the length of each iovec so that the start
* of the next one is naturally aligned. We'll need to
* account for that slack space here. Then round nbytes up
* to 64-bit alignment so that the initial buffer alignment is
* easy to calculate and verify.
*/
nbytes += niovecs * sizeof(uint64_t);
nbytes = round_up(nbytes, sizeof(uint64_t));
/*
* The data buffer needs to start 64-bit aligned, so round up
* that space to ensure we can align it appropriately and not
* overrun the buffer.
*/
buf_size = nbytes + xlog_cil_iovec_space(niovecs);
/*
* if we have no shadow buffer, or it is too small, we need to
* reallocate it.
*/
if (!lip->li_lv_shadow ||
buf_size > lip->li_lv_shadow->lv_size) {
/*
* We free and allocate here as a realloc would copy
* unecessary data. We don't use kmem_zalloc() for the
* same reason - we don't need to zero the data area in
* the buffer, only the log vector header and the iovec
* storage.
*/
kmem_free(lip->li_lv_shadow);
lv = kmem_alloc(buf_size, KM_SLEEP|KM_NOFS);
memset(lv, 0, xlog_cil_iovec_space(niovecs));
lv->lv_item = lip;
lv->lv_size = buf_size;
if (ordered)
lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
else
lv->lv_iovecp = (struct xfs_log_iovec *)&lv[1];
lip->li_lv_shadow = lv;
} else {
/* same or smaller, optimise common overwrite case */
lv = lip->li_lv_shadow;
if (ordered)
lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
else
lv->lv_buf_len = 0;
lv->lv_bytes = 0;
lv->lv_next = NULL;
}
/* Ensure the lv is set up according to ->iop_size */
lv->lv_niovecs = niovecs;
/* The allocated data region lies beyond the iovec region */
lv->lv_buf = (char *)lv + xlog_cil_iovec_space(niovecs);
}
}
/*
* Prepare the log item for insertion into the CIL. Calculate the difference in
* log space and vectors it will consume, and if it is a new item pin it as
* well.
*/
STATIC void
xfs_cil_prepare_item(
struct xlog *log,
struct xfs_log_vec *lv,
struct xfs_log_vec *old_lv,
int *diff_len,
int *diff_iovecs)
{
/* Account for the new LV being passed in */
if (lv->lv_buf_len != XFS_LOG_VEC_ORDERED) {
*diff_len += lv->lv_bytes;
*diff_iovecs += lv->lv_niovecs;
}
/*
* If there is no old LV, this is the first time we've seen the item in
* this CIL context and so we need to pin it. If we are replacing the
* old_lv, then remove the space it accounts for and make it the shadow
* buffer for later freeing. In both cases we are now switching to the
* shadow buffer, so update the the pointer to it appropriately.
*/
if (!old_lv) {
lv->lv_item->li_ops->iop_pin(lv->lv_item);
lv->lv_item->li_lv_shadow = NULL;
} else if (old_lv != lv) {
ASSERT(lv->lv_buf_len != XFS_LOG_VEC_ORDERED);
*diff_len -= old_lv->lv_bytes;
*diff_iovecs -= old_lv->lv_niovecs;
lv->lv_item->li_lv_shadow = old_lv;
}
/* attach new log vector to log item */
lv->lv_item->li_lv = lv;
/*
* If this is the first time the item is being committed to the
* CIL, store the sequence number on the log item so we can
* tell in future commits whether this is the first checkpoint
* the item is being committed into.
*/
if (!lv->lv_item->li_seq)
lv->lv_item->li_seq = log->l_cilp->xc_ctx->sequence;
}
/*
* Format log item into a flat buffers
*
* For delayed logging, we need to hold a formatted buffer containing all the
* changes on the log item. This enables us to relog the item in memory and
* write it out asynchronously without needing to relock the object that was
* modified at the time it gets written into the iclog.
*
* This function takes the prepared log vectors attached to each log item, and
* formats the changes into the log vector buffer. The buffer it uses is
* dependent on the current state of the vector in the CIL - the shadow lv is
* guaranteed to be large enough for the current modification, but we will only
* use that if we can't reuse the existing lv. If we can't reuse the existing
* lv, then simple swap it out for the shadow lv. We don't free it - that is
* done lazily either by th enext modification or the freeing of the log item.
*
* We don't set up region headers during this process; we simply copy the
* regions into the flat buffer. We can do this because we still have to do a
* formatting step to write the regions into the iclog buffer. Writing the
* ophdrs during the iclog write means that we can support splitting large
* regions across iclog boundares without needing a change in the format of the
* item/region encapsulation.
*
* Hence what we need to do now is change the rewrite the vector array to point
* to the copied region inside the buffer we just allocated. This allows us to
* format the regions into the iclog as though they are being formatted
* directly out of the objects themselves.
*/
static void
xlog_cil_insert_format_items(
struct xlog *log,
struct xfs_trans *tp,
int *diff_len,
int *diff_iovecs)
{
struct xfs_log_item_desc *lidp;
/* Bail out if we didn't find a log item. */
if (list_empty(&tp->t_items)) {
ASSERT(0);
return;
}
list_for_each_entry(lidp, &tp->t_items, lid_trans) {
struct xfs_log_item *lip = lidp->lid_item;
struct xfs_log_vec *lv;
struct xfs_log_vec *old_lv = NULL;
struct xfs_log_vec *shadow;
bool ordered = false;
/* Skip items which aren't dirty in this transaction. */
if (!(lidp->lid_flags & XFS_LID_DIRTY))
continue;
/*
* The formatting size information is already attached to
* the shadow lv on the log item.
*/
shadow = lip->li_lv_shadow;
if (shadow->lv_buf_len == XFS_LOG_VEC_ORDERED)
ordered = true;
/* Skip items that do not have any vectors for writing */
if (!shadow->lv_niovecs && !ordered)
continue;
/* compare to existing item size */
old_lv = lip->li_lv;
if (lip->li_lv && shadow->lv_size <= lip->li_lv->lv_size) {
/* same or smaller, optimise common overwrite case */
lv = lip->li_lv;
lv->lv_next = NULL;
if (ordered)
goto insert;
/*
* set the item up as though it is a new insertion so
* that the space reservation accounting is correct.
*/
*diff_iovecs -= lv->lv_niovecs;
*diff_len -= lv->lv_bytes;
/* Ensure the lv is set up according to ->iop_size */
lv->lv_niovecs = shadow->lv_niovecs;
/* reset the lv buffer information for new formatting */
lv->lv_buf_len = 0;
lv->lv_bytes = 0;
lv->lv_buf = (char *)lv +
xlog_cil_iovec_space(lv->lv_niovecs);
} else {
/* switch to shadow buffer! */
lv = shadow;
lv->lv_item = lip;
if (ordered) {
/* track as an ordered logvec */
ASSERT(lip->li_lv == NULL);
goto insert;
}
}
ASSERT(IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t)));
lip->li_ops->iop_format(lip, lv);
insert:
xfs_cil_prepare_item(log, lv, old_lv, diff_len, diff_iovecs);
}
}
/*
* Insert the log items into the CIL and calculate the difference in space
* consumed by the item. Add the space to the checkpoint ticket and calculate
* if the change requires additional log metadata. If it does, take that space
* as well. Remove the amount of space we added to the checkpoint ticket from
* the current transaction ticket so that the accounting works out correctly.
*/
static void
xlog_cil_insert_items(
struct xlog *log,
struct xfs_trans *tp)
{
struct xfs_cil *cil = log->l_cilp;
struct xfs_cil_ctx *ctx = cil->xc_ctx;
struct xfs_log_item_desc *lidp;
int len = 0;
int diff_iovecs = 0;
int iclog_space;
ASSERT(tp);
/*
* We can do this safely because the context can't checkpoint until we
* are done so it doesn't matter exactly how we update the CIL.
*/
xlog_cil_insert_format_items(log, tp, &len, &diff_iovecs);
/*
* Now (re-)position everything modified at the tail of the CIL.
* We do this here so we only need to take the CIL lock once during
* the transaction commit.
*/
spin_lock(&cil->xc_cil_lock);
list_for_each_entry(lidp, &tp->t_items, lid_trans) {
struct xfs_log_item *lip = lidp->lid_item;
/* Skip items which aren't dirty in this transaction. */
if (!(lidp->lid_flags & XFS_LID_DIRTY))
continue;
/*
* Only move the item if it isn't already at the tail. This is
* to prevent a transient list_empty() state when reinserting
* an item that is already the only item in the CIL.
*/
if (!list_is_last(&lip->li_cil, &cil->xc_cil))
list_move_tail(&lip->li_cil, &cil->xc_cil);
}
/* account for space used by new iovec headers */
len += diff_iovecs * sizeof(xlog_op_header_t);
ctx->nvecs += diff_iovecs;
/* attach the transaction to the CIL if it has any busy extents */
if (!list_empty(&tp->t_busy))
list_splice_init(&tp->t_busy, &ctx->busy_extents);
/*
* Now transfer enough transaction reservation to the context ticket
* for the checkpoint. The context ticket is special - the unit
* reservation has to grow as well as the current reservation as we
* steal from tickets so we can correctly determine the space used
* during the transaction commit.
*/
if (ctx->ticket->t_curr_res == 0) {
ctx->ticket->t_curr_res = ctx->ticket->t_unit_res;
tp->t_ticket->t_curr_res -= ctx->ticket->t_unit_res;
}
/* do we need space for more log record headers? */
iclog_space = log->l_iclog_size - log->l_iclog_hsize;
if (len > 0 && (ctx->space_used / iclog_space !=
(ctx->space_used + len) / iclog_space)) {
int hdrs;
hdrs = (len + iclog_space - 1) / iclog_space;
/* need to take into account split region headers, too */
hdrs *= log->l_iclog_hsize + sizeof(struct xlog_op_header);
ctx->ticket->t_unit_res += hdrs;
ctx->ticket->t_curr_res += hdrs;
tp->t_ticket->t_curr_res -= hdrs;
ASSERT(tp->t_ticket->t_curr_res >= len);
}
tp->t_ticket->t_curr_res -= len;
ctx->space_used += len;
spin_unlock(&cil->xc_cil_lock);
}
static void
xlog_cil_free_logvec(
struct xfs_log_vec *log_vector)
{
struct xfs_log_vec *lv;
for (lv = log_vector; lv; ) {
struct xfs_log_vec *next = lv->lv_next;
kmem_free(lv);
lv = next;
}
}
/*
* Mark all items committed and clear busy extents. We free the log vector
* chains in a separate pass so that we unpin the log items as quickly as
* possible.
*/
static void
xlog_cil_committed(
void *args,
int abort)
{
struct xfs_cil_ctx *ctx = args;
struct xfs_mount *mp = ctx->cil->xc_log->l_mp;
xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
ctx->start_lsn, abort);
xfs_extent_busy_sort(&ctx->busy_extents);
xfs_extent_busy_clear(mp, &ctx->busy_extents,
(mp->m_flags & XFS_MOUNT_DISCARD) && !abort);
/*
* If we are aborting the commit, wake up anyone waiting on the
* committing list. If we don't, then a shutdown we can leave processes
* waiting in xlog_cil_force_lsn() waiting on a sequence commit that
* will never happen because we aborted it.
*/
spin_lock(&ctx->cil->xc_push_lock);
if (abort)
wake_up_all(&ctx->cil->xc_commit_wait);
list_del(&ctx->committing);
spin_unlock(&ctx->cil->xc_push_lock);
xlog_cil_free_logvec(ctx->lv_chain);
if (!list_empty(&ctx->busy_extents)) {
ASSERT(mp->m_flags & XFS_MOUNT_DISCARD);
xfs_discard_extents(mp, &ctx->busy_extents);
xfs_extent_busy_clear(mp, &ctx->busy_extents, false);
}
kmem_free(ctx);
}
/*
* Push the Committed Item List to the log. If @push_seq flag is zero, then it
* is a background flush and so we can chose to ignore it. Otherwise, if the
* current sequence is the same as @push_seq we need to do a flush. If
* @push_seq is less than the current sequence, then it has already been
* flushed and we don't need to do anything - the caller will wait for it to
* complete if necessary.
*
* @push_seq is a value rather than a flag because that allows us to do an
* unlocked check of the sequence number for a match. Hence we can allows log
* forces to run racily and not issue pushes for the same sequence twice. If we
* get a race between multiple pushes for the same sequence they will block on
* the first one and then abort, hence avoiding needless pushes.
*/
STATIC int
xlog_cil_push(
struct xlog *log)
{
struct xfs_cil *cil = log->l_cilp;
struct xfs_log_vec *lv;
struct xfs_cil_ctx *ctx;
struct xfs_cil_ctx *new_ctx;
struct xlog_in_core *commit_iclog;
struct xlog_ticket *tic;
int num_iovecs;
int error = 0;
struct xfs_trans_header thdr;
struct xfs_log_iovec lhdr;
struct xfs_log_vec lvhdr = { NULL };
xfs_lsn_t commit_lsn;
xfs_lsn_t push_seq;
if (!cil)
return 0;
new_ctx = kmem_zalloc(sizeof(*new_ctx), KM_SLEEP|KM_NOFS);
new_ctx->ticket = xlog_cil_ticket_alloc(log);
down_write(&cil->xc_ctx_lock);
ctx = cil->xc_ctx;
spin_lock(&cil->xc_push_lock);
push_seq = cil->xc_push_seq;
ASSERT(push_seq <= ctx->sequence);
/*
* Check if we've anything to push. If there is nothing, then we don't
* move on to a new sequence number and so we have to be able to push
* this sequence again later.
*/
if (list_empty(&cil->xc_cil)) {
cil->xc_push_seq = 0;
spin_unlock(&cil->xc_push_lock);
goto out_skip;
}
/* check for a previously pushed seqeunce */
if (push_seq < cil->xc_ctx->sequence) {
spin_unlock(&cil->xc_push_lock);
goto out_skip;
}
/*
* We are now going to push this context, so add it to the committing
* list before we do anything else. This ensures that anyone waiting on
* this push can easily detect the difference between a "push in
* progress" and "CIL is empty, nothing to do".
*
* IOWs, a wait loop can now check for:
* the current sequence not being found on the committing list;
* an empty CIL; and
* an unchanged sequence number
* to detect a push that had nothing to do and therefore does not need
* waiting on. If the CIL is not empty, we get put on the committing
* list before emptying the CIL and bumping the sequence number. Hence
* an empty CIL and an unchanged sequence number means we jumped out
* above after doing nothing.
*
* Hence the waiter will either find the commit sequence on the
* committing list or the sequence number will be unchanged and the CIL
* still dirty. In that latter case, the push has not yet started, and
* so the waiter will have to continue trying to check the CIL
* committing list until it is found. In extreme cases of delay, the
* sequence may fully commit between the attempts the wait makes to wait
* on the commit sequence.
*/
list_add(&ctx->committing, &cil->xc_committing);
spin_unlock(&cil->xc_push_lock);
/*
* pull all the log vectors off the items in the CIL, and
* remove the items from the CIL. We don't need the CIL lock
* here because it's only needed on the transaction commit
* side which is currently locked out by the flush lock.
*/
lv = NULL;
num_iovecs = 0;
while (!list_empty(&cil->xc_cil)) {
struct xfs_log_item *item;
item = list_first_entry(&cil->xc_cil,
struct xfs_log_item, li_cil);
list_del_init(&item->li_cil);
if (!ctx->lv_chain)
ctx->lv_chain = item->li_lv;
else
lv->lv_next = item->li_lv;
lv = item->li_lv;
item->li_lv = NULL;
num_iovecs += lv->lv_niovecs;
}
/*
* initialise the new context and attach it to the CIL. Then attach
* the current context to the CIL committing lsit so it can be found
* during log forces to extract the commit lsn of the sequence that
* needs to be forced.
*/
INIT_LIST_HEAD(&new_ctx->committing);
INIT_LIST_HEAD(&new_ctx->busy_extents);
new_ctx->sequence = ctx->sequence + 1;
new_ctx->cil = cil;
cil->xc_ctx = new_ctx;
/*
* The switch is now done, so we can drop the context lock and move out
* of a shared context. We can't just go straight to the commit record,
* though - we need to synchronise with previous and future commits so
* that the commit records are correctly ordered in the log to ensure
* that we process items during log IO completion in the correct order.
*
* For example, if we get an EFI in one checkpoint and the EFD in the
* next (e.g. due to log forces), we do not want the checkpoint with
* the EFD to be committed before the checkpoint with the EFI. Hence
* we must strictly order the commit records of the checkpoints so
* that: a) the checkpoint callbacks are attached to the iclogs in the
* correct order; and b) the checkpoints are replayed in correct order
* in log recovery.
*
* Hence we need to add this context to the committing context list so
* that higher sequences will wait for us to write out a commit record
* before they do.
*
* xfs_log_force_lsn requires us to mirror the new sequence into the cil
* structure atomically with the addition of this sequence to the
* committing list. This also ensures that we can do unlocked checks
* against the current sequence in log forces without risking
* deferencing a freed context pointer.
*/
spin_lock(&cil->xc_push_lock);
cil->xc_current_sequence = new_ctx->sequence;
spin_unlock(&cil->xc_push_lock);
up_write(&cil->xc_ctx_lock);
/*
* Build a checkpoint transaction header and write it to the log to
* begin the transaction. We need to account for the space used by the
* transaction header here as it is not accounted for in xlog_write().
*
* The LSN we need to pass to the log items on transaction commit is
* the LSN reported by the first log vector write. If we use the commit
* record lsn then we can move the tail beyond the grant write head.
*/
tic = ctx->ticket;
thdr.th_magic = XFS_TRANS_HEADER_MAGIC;
thdr.th_type = XFS_TRANS_CHECKPOINT;
thdr.th_tid = tic->t_tid;
thdr.th_num_items = num_iovecs;
lhdr.i_addr = &thdr;
lhdr.i_len = sizeof(xfs_trans_header_t);
lhdr.i_type = XLOG_REG_TYPE_TRANSHDR;
tic->t_curr_res -= lhdr.i_len + sizeof(xlog_op_header_t);
lvhdr.lv_niovecs = 1;
lvhdr.lv_iovecp = &lhdr;
lvhdr.lv_next = ctx->lv_chain;
error = xlog_write(log, &lvhdr, tic, &ctx->start_lsn, NULL, 0);
if (error)
goto out_abort_free_ticket;
/*
* now that we've written the checkpoint into the log, strictly
* order the commit records so replay will get them in the right order.
*/
restart:
spin_lock(&cil->xc_push_lock);
list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
/*
* Avoid getting stuck in this loop because we were woken by the
* shutdown, but then went back to sleep once already in the
* shutdown state.
*/
if (XLOG_FORCED_SHUTDOWN(log)) {
spin_unlock(&cil->xc_push_lock);
goto out_abort_free_ticket;
}
/*
* Higher sequences will wait for this one so skip them.
* Don't wait for our own sequence, either.
*/
if (new_ctx->sequence >= ctx->sequence)
continue;
if (!new_ctx->commit_lsn) {
/*
* It is still being pushed! Wait for the push to
* complete, then start again from the beginning.
*/
xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
goto restart;
}
}
spin_unlock(&cil->xc_push_lock);
/* xfs_log_done always frees the ticket on error. */
commit_lsn = xfs_log_done(log->l_mp, tic, &commit_iclog, false);
if (commit_lsn == -1)
goto out_abort;
/* attach all the transactions w/ busy extents to iclog */
ctx->log_cb.cb_func = xlog_cil_committed;
ctx->log_cb.cb_arg = ctx;
error = xfs_log_notify(log->l_mp, commit_iclog, &ctx->log_cb);
if (error)
goto out_abort;
/*
* now the checkpoint commit is complete and we've attached the
* callbacks to the iclog we can assign the commit LSN to the context
* and wake up anyone who is waiting for the commit to complete.
*/
spin_lock(&cil->xc_push_lock);
ctx->commit_lsn = commit_lsn;
wake_up_all(&cil->xc_commit_wait);
spin_unlock(&cil->xc_push_lock);
/* release the hounds! */
return xfs_log_release_iclog(log->l_mp, commit_iclog);
out_skip:
up_write(&cil->xc_ctx_lock);
xfs_log_ticket_put(new_ctx->ticket);
kmem_free(new_ctx);
return 0;
out_abort_free_ticket:
xfs_log_ticket_put(tic);
out_abort:
xlog_cil_committed(ctx, XFS_LI_ABORTED);
return -EIO;
}
static void
xlog_cil_push_work(
struct work_struct *work)
{
struct xfs_cil *cil = container_of(work, struct xfs_cil,
xc_push_work);
xlog_cil_push(cil->xc_log);
}
/*
* We need to push CIL every so often so we don't cache more than we can fit in
* the log. The limit really is that a checkpoint can't be more than half the
* log (the current checkpoint is not allowed to overwrite the previous
* checkpoint), but commit latency and memory usage limit this to a smaller
* size.
*/
static void
xlog_cil_push_background(
struct xlog *log)
{
struct xfs_cil *cil = log->l_cilp;
/*
* The cil won't be empty because we are called while holding the
* context lock so whatever we added to the CIL will still be there
*/
ASSERT(!list_empty(&cil->xc_cil));
/*
* don't do a background push if we haven't used up all the
* space available yet.
*/
if (cil->xc_ctx->space_used < XLOG_CIL_SPACE_LIMIT(log))
return;
spin_lock(&cil->xc_push_lock);
if (cil->xc_push_seq < cil->xc_current_sequence) {
cil->xc_push_seq = cil->xc_current_sequence;
queue_work(log->l_mp->m_cil_workqueue, &cil->xc_push_work);
}
spin_unlock(&cil->xc_push_lock);
}
/*
* xlog_cil_push_now() is used to trigger an immediate CIL push to the sequence
* number that is passed. When it returns, the work will be queued for
* @push_seq, but it won't be completed. The caller is expected to do any
* waiting for push_seq to complete if it is required.
*/
static void
xlog_cil_push_now(
struct xlog *log,
xfs_lsn_t push_seq)
{
struct xfs_cil *cil = log->l_cilp;
if (!cil)
return;
ASSERT(push_seq && push_seq <= cil->xc_current_sequence);
/* start on any pending background push to minimise wait time on it */
flush_work(&cil->xc_push_work);
/*
* If the CIL is empty or we've already pushed the sequence then
* there's no work we need to do.
*/
spin_lock(&cil->xc_push_lock);
if (list_empty(&cil->xc_cil) || push_seq <= cil->xc_push_seq) {
spin_unlock(&cil->xc_push_lock);
return;
}
cil->xc_push_seq = push_seq;
queue_work(log->l_mp->m_cil_workqueue, &cil->xc_push_work);
spin_unlock(&cil->xc_push_lock);
}
bool
xlog_cil_empty(
struct xlog *log)
{
struct xfs_cil *cil = log->l_cilp;
bool empty = false;
spin_lock(&cil->xc_push_lock);
if (list_empty(&cil->xc_cil))
empty = true;
spin_unlock(&cil->xc_push_lock);
return empty;
}
/*
* Commit a transaction with the given vector to the Committed Item List.
*
* To do this, we need to format the item, pin it in memory if required and
* account for the space used by the transaction. Once we have done that we
* need to release the unused reservation for the transaction, attach the
* transaction to the checkpoint context so we carry the busy extents through
* to checkpoint completion, and then unlock all the items in the transaction.
*
* Called with the context lock already held in read mode to lock out
* background commit, returns without it held once background commits are
* allowed again.
*/
void
xfs_log_commit_cil(
struct xfs_mount *mp,
struct xfs_trans *tp,
xfs_lsn_t *commit_lsn,
bool regrant)
{
struct xlog *log = mp->m_log;
struct xfs_cil *cil = log->l_cilp;
/*
* Do all necessary memory allocation before we lock the CIL.
* This ensures the allocation does not deadlock with a CIL
* push in memory reclaim (e.g. from kswapd).
*/
xlog_cil_alloc_shadow_bufs(log, tp);
/* lock out background commit */
down_read(&cil->xc_ctx_lock);
xlog_cil_insert_items(log, tp);
/* check we didn't blow the reservation */
if (tp->t_ticket->t_curr_res < 0)
xlog_print_tic_res(mp, tp->t_ticket);
tp->t_commit_lsn = cil->xc_ctx->sequence;
if (commit_lsn)
*commit_lsn = tp->t_commit_lsn;
xfs_log_done(mp, tp->t_ticket, NULL, regrant);
xfs_trans_unreserve_and_mod_sb(tp);
/*
* Once all the items of the transaction have been copied to the CIL,
* the items can be unlocked and freed.
*
* This needs to be done before we drop the CIL context lock because we
* have to update state in the log items and unlock them before they go
* to disk. If we don't, then the CIL checkpoint can race with us and
* we can run checkpoint completion before we've updated and unlocked
* the log items. This affects (at least) processing of stale buffers,
* inodes and EFIs.
*/
xfs_trans_free_items(tp, tp->t_commit_lsn, false);
xlog_cil_push_background(log);
up_read(&cil->xc_ctx_lock);
}
/*
* Conditionally push the CIL based on the sequence passed in.
*
* We only need to push if we haven't already pushed the sequence
* number given. Hence the only time we will trigger a push here is
* if the push sequence is the same as the current context.
*
* We return the current commit lsn to allow the callers to determine if a
* iclog flush is necessary following this call.
*/
xfs_lsn_t
xlog_cil_force_lsn(
struct xlog *log,
xfs_lsn_t sequence)
{
struct xfs_cil *cil = log->l_cilp;
struct xfs_cil_ctx *ctx;
xfs_lsn_t commit_lsn = NULLCOMMITLSN;
ASSERT(sequence <= cil->xc_current_sequence);
/*
* check to see if we need to force out the current context.
* xlog_cil_push() handles racing pushes for the same sequence,
* so no need to deal with it here.
*/
restart:
xlog_cil_push_now(log, sequence);
/*
* See if we can find a previous sequence still committing.
* We need to wait for all previous sequence commits to complete
* before allowing the force of push_seq to go ahead. Hence block
* on commits for those as well.
*/
spin_lock(&cil->xc_push_lock);
list_for_each_entry(ctx, &cil->xc_committing, committing) {
/*
* Avoid getting stuck in this loop because we were woken by the
* shutdown, but then went back to sleep once already in the
* shutdown state.
*/
if (XLOG_FORCED_SHUTDOWN(log))
goto out_shutdown;
if (ctx->sequence > sequence)
continue;
if (!ctx->commit_lsn) {
/*
* It is still being pushed! Wait for the push to
* complete, then start again from the beginning.
*/
xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
goto restart;
}
if (ctx->sequence != sequence)
continue;
/* found it! */
commit_lsn = ctx->commit_lsn;
}
/*
* The call to xlog_cil_push_now() executes the push in the background.
* Hence by the time we have got here it our sequence may not have been
* pushed yet. This is true if the current sequence still matches the
* push sequence after the above wait loop and the CIL still contains
* dirty objects. This is guaranteed by the push code first adding the
* context to the committing list before emptying the CIL.
*
* Hence if we don't find the context in the committing list and the
* current sequence number is unchanged then the CIL contents are
* significant. If the CIL is empty, if means there was nothing to push
* and that means there is nothing to wait for. If the CIL is not empty,
* it means we haven't yet started the push, because if it had started
* we would have found the context on the committing list.
*/
if (sequence == cil->xc_current_sequence &&
!list_empty(&cil->xc_cil)) {
spin_unlock(&cil->xc_push_lock);
goto restart;
}
spin_unlock(&cil->xc_push_lock);
return commit_lsn;
/*
* We detected a shutdown in progress. We need to trigger the log force
* to pass through it's iclog state machine error handling, even though
* we are already in a shutdown state. Hence we can't return
* NULLCOMMITLSN here as that has special meaning to log forces (i.e.
* LSN is already stable), so we return a zero LSN instead.
*/
out_shutdown:
spin_unlock(&cil->xc_push_lock);
return 0;
}
/*
* Check if the current log item was first committed in this sequence.
* We can't rely on just the log item being in the CIL, we have to check
* the recorded commit sequence number.
*
* Note: for this to be used in a non-racy manner, it has to be called with
* CIL flushing locked out. As a result, it should only be used during the
* transaction commit process when deciding what to format into the item.
*/
bool
xfs_log_item_in_current_chkpt(
struct xfs_log_item *lip)
{
struct xfs_cil_ctx *ctx;
if (list_empty(&lip->li_cil))
return false;
ctx = lip->li_mountp->m_log->l_cilp->xc_ctx;
/*
* li_seq is written on the first commit of a log item to record the
* first checkpoint it is written to. Hence if it is different to the
* current sequence, we're in a new checkpoint.
*/
if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0)
return false;
return true;
}
/*
* Perform initial CIL structure initialisation.
*/
int
xlog_cil_init(
struct xlog *log)
{
struct xfs_cil *cil;
struct xfs_cil_ctx *ctx;
cil = kmem_zalloc(sizeof(*cil), KM_SLEEP|KM_MAYFAIL);
if (!cil)
return -ENOMEM;
ctx = kmem_zalloc(sizeof(*ctx), KM_SLEEP|KM_MAYFAIL);
if (!ctx) {
kmem_free(cil);
return -ENOMEM;
}
INIT_WORK(&cil->xc_push_work, xlog_cil_push_work);
INIT_LIST_HEAD(&cil->xc_cil);
INIT_LIST_HEAD(&cil->xc_committing);
spin_lock_init(&cil->xc_cil_lock);
spin_lock_init(&cil->xc_push_lock);
init_rwsem(&cil->xc_ctx_lock);
init_waitqueue_head(&cil->xc_commit_wait);
INIT_LIST_HEAD(&ctx->committing);
INIT_LIST_HEAD(&ctx->busy_extents);
ctx->sequence = 1;
ctx->cil = cil;
cil->xc_ctx = ctx;
cil->xc_current_sequence = ctx->sequence;
cil->xc_log = log;
log->l_cilp = cil;
return 0;
}
void
xlog_cil_destroy(
struct xlog *log)
{
if (log->l_cilp->xc_ctx) {
if (log->l_cilp->xc_ctx->ticket)
xfs_log_ticket_put(log->l_cilp->xc_ctx->ticket);
kmem_free(log->l_cilp->xc_ctx);
}
ASSERT(list_empty(&log->l_cilp->xc_cil));
kmem_free(log->l_cilp);
}