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SubjectRe: [PATCH v7.1] block: Coordinate flush requests
Hello,

On Tue, Jan 18, 2011 at 09:12:55AM +0800, Shaohua Li wrote:
> This makes sense. would it possible N flush data payloads delay the
> first request?

I ended up with a different design. Still buggy. It triggers a weird
oops under stress test but other than that things generally seem to
work as expected. Please read the comment at the top of blk-flush.c
for more info. I'll post properly after more testing and debugging.

Thanks.

Index: work/block/blk-core.c
===================================================================
--- work.orig/block/blk-core.c
+++ work/block/blk-core.c
@@ -149,39 +149,29 @@ EXPORT_SYMBOL(blk_rq_init);
static void req_bio_endio(struct request *rq, struct bio *bio,
unsigned int nbytes, int error)
{
- struct request_queue *q = rq->q;
+ if (error)
+ clear_bit(BIO_UPTODATE, &bio->bi_flags);
+ else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
+ error = -EIO;

- if (&q->flush_rq != rq) {
- if (error)
- clear_bit(BIO_UPTODATE, &bio->bi_flags);
- else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
- error = -EIO;
-
- if (unlikely(nbytes > bio->bi_size)) {
- printk(KERN_ERR "%s: want %u bytes done, %u left\n",
- __func__, nbytes, bio->bi_size);
- nbytes = bio->bi_size;
- }
+ if (unlikely(nbytes > bio->bi_size)) {
+ printk(KERN_ERR "%s: want %u bytes done, %u left\n",
+ __func__, nbytes, bio->bi_size);
+ nbytes = bio->bi_size;
+ }

- if (unlikely(rq->cmd_flags & REQ_QUIET))
- set_bit(BIO_QUIET, &bio->bi_flags);
+ if (unlikely(rq->cmd_flags & REQ_QUIET))
+ set_bit(BIO_QUIET, &bio->bi_flags);

- bio->bi_size -= nbytes;
- bio->bi_sector += (nbytes >> 9);
+ bio->bi_size -= nbytes;
+ bio->bi_sector += (nbytes >> 9);

- if (bio_integrity(bio))
- bio_integrity_advance(bio, nbytes);
+ if (bio_integrity(bio))
+ bio_integrity_advance(bio, nbytes);

- if (bio->bi_size == 0)
- bio_endio(bio, error);
- } else {
- /*
- * Okay, this is the sequenced flush request in
- * progress, just record the error;
- */
- if (error && !q->flush_err)
- q->flush_err = error;
- }
+ /* don't actually finish bio if it's part of flush sequence */
+ if (bio->bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ))
+ bio_endio(bio, error);
}

void blk_dump_rq_flags(struct request *rq, char *msg)
@@ -540,7 +530,9 @@ struct request_queue *blk_alloc_queue_no
init_timer(&q->unplug_timer);
setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
INIT_LIST_HEAD(&q->timeout_list);
- INIT_LIST_HEAD(&q->pending_flushes);
+ INIT_LIST_HEAD(&q->flush_queue[0]);
+ INIT_LIST_HEAD(&q->flush_queue[1]);
+ INIT_LIST_HEAD(&q->flush_data_in_flight);
INIT_WORK(&q->unplug_work, blk_unplug_work);

kobject_init(&q->kobj, &blk_queue_ktype);
@@ -1219,7 +1211,7 @@ static int __make_request(struct request
spin_lock_irq(q->queue_lock);

if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
- where = ELEVATOR_INSERT_FRONT;
+ where = ELEVATOR_INSERT_FLUSH;
goto get_rq;
}

@@ -1804,7 +1796,7 @@ static void blk_account_io_done(struct r
* normal IO on queueing nor completion. Accounting the
* containing request is enough.
*/
- if (blk_do_io_stat(req) && req != &req->q->flush_rq) {
+ if (blk_do_io_stat(req) && !(req->cmd_flags & REQ_FLUSH_SEQ)) {
unsigned long duration = jiffies - req->start_time;
const int rw = rq_data_dir(req);
struct hd_struct *part;
Index: work/block/blk-flush.c
===================================================================
--- work.orig/block/blk-flush.c
+++ work/block/blk-flush.c
@@ -1,6 +1,66 @@
/*
* Functions to sequence FLUSH and FUA writes.
+ *
+ * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
+ * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
+ *
+ * This file is released under the GPLv2.
+ *
+ * REQ_{FLUSH|FUA} requests are decomposed to sequences composed of three
+ * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
+ * properties and hardware capability.
+ *
+ * If a request doesn't have data, only REQ_FLUSH makes sense, which
+ * indicates a simple flush request. If there is data, REQ_FLUSH indicates
+ * that the device cache should be flushed before the data is executed, and
+ * REQ_FUA means that the data must be on non-volatile media on request
+ * completion.
+ *
+ * If the device doesn't have writeback cache, FLUSH and FUA don't make any
+ * difference. The requests are either completed immediately if there's no
+ * data or executed as normal requests.
+ *
+ * If the device has writeback cache and supports FUA, REQ_FLUSH is
+ * translated to PREFLUSH but REQ_FUA is passed down directly with the data
+ * request.
+ *
+ * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
+ * translated to PREFLUSH and REQ_FUA to POSTFLUSH.
+ *
+ * The actual execution of flush is double buffered. Whenever a request
+ * needs to execute PRE or POSTFLUSH, it queues at
+ * q->flush_queue[q->flush_pending_idx]. Once certain criteria are met,
+ * flush is issued and pending_idx is toggled. When the flush completes,
+ * all the requests which were pending are proceeded to the next step.
+ * This allows near optimal merging of flush requests.
+ *
+ * Currently, the following conditions are used to determine when to issue
+ * flush.
+ *
+ * C1. At any given time, only one flush shall be in progress. This makes
+ * double buffering sufficient.
+ *
+ * C2. Flush is not deferred if any request is executing the data part of
+ * its sequence. This avoids issuing separate POSTFLUSHes for requests
+ * which shared PREFLUSH.
+ *
+ * C3. The second condition is ignored if there is a request which has
+ * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
+ * starvation in the unlikely case where there are continuous stream of
+ * FUA (without FLUSH) requests.
+ *
+ * Note that a sequenced FLUSH/FUA request with data is completed twice.
+ * Once while executing the data part and again after the whole sequence is
+ * complete. The first completion updates the contained bio but doesn't
+ * finish it so that the bio submitter is notified only after the whole
+ * sequence is complete. This is implemented by testing REQ_FLUSH_SEQ in
+ * req_bio_endio().
+ *
+ * The above peculiarity requires that each FLUSH/FUA request has only one
+ * bio attached to it, which is guaranteed as they aren't allowed to be
+ * merged in the usual way.
*/
+
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
@@ -11,184 +71,289 @@

/* FLUSH/FUA sequences */
enum {
- QUEUE_FSEQ_STARTED = (1 << 0), /* flushing in progress */
- QUEUE_FSEQ_PREFLUSH = (1 << 1), /* pre-flushing in progress */
- QUEUE_FSEQ_DATA = (1 << 2), /* data write in progress */
- QUEUE_FSEQ_POSTFLUSH = (1 << 3), /* post-flushing in progress */
- QUEUE_FSEQ_DONE = (1 << 4),
+ REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
+ REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
+ REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
+ REQ_FSEQ_DONE = (1 << 3),
+
+ REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
+ REQ_FSEQ_POSTFLUSH,
+
+ /*
+ * If flush has been pending longer than the following timeout,
+ * it's issued even if flush_data requests are still in flight.
+ */
+ FLUSH_PENDING_TIMEOUT = 5 * HZ,
};

-static struct request *queue_next_fseq(struct request_queue *q);
+static bool blk_kick_flush(struct request_queue *q);

-unsigned blk_flush_cur_seq(struct request_queue *q)
+static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
{
- if (!q->flush_seq)
- return 0;
- return 1 << ffz(q->flush_seq);
+ unsigned int policy = 0;
+
+ if (fflags & REQ_FLUSH) {
+ if (rq->cmd_flags & REQ_FLUSH)
+ policy |= REQ_FSEQ_PREFLUSH;
+ if (blk_rq_sectors(rq))
+ policy |= REQ_FSEQ_DATA;
+ if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
+ policy |= REQ_FSEQ_POSTFLUSH;
+ }
+ return policy;
}

-static struct request *blk_flush_complete_seq(struct request_queue *q,
- unsigned seq, int error)
+static unsigned int blk_flush_cur_seq(struct request *rq)
{
- struct request *next_rq = NULL;
+ return 1 << ffz(rq->flush.seq);
+}

- if (error && !q->flush_err)
- q->flush_err = error;
+static void blk_flush_restore_request(struct request *rq)
+{
+ /*
+ * After flush data completion, @rq->bio is %NULL but we need to
+ * complete the bio again. @rq->biotail is guaranteed to equal the
+ * original @rq->bio. Restore it.
+ */
+ rq->bio = rq->biotail;

- BUG_ON(q->flush_seq & seq);
- q->flush_seq |= seq;
+ /* make @rq a normal request */
+ rq->cmd_flags &= ~REQ_FLUSH_SEQ;
+ rq->end_io = NULL;
+}

- if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) {
- /* not complete yet, queue the next flush sequence */
- next_rq = queue_next_fseq(q);
- } else {
- /* complete this flush request */
- __blk_end_request_all(q->orig_flush_rq, q->flush_err);
- q->orig_flush_rq = NULL;
- q->flush_seq = 0;
+/**
+ * blk_flush_complete_seq - complete flush sequence
+ * @rq: FLUSH/FUA request being sequenced
+ * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
+ * @error: whether an error occurred
+ *
+ * @rq just completed @seq part of its flush sequence, record the
+ * completion and trigger the next step.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock)
+ *
+ * RETURNS:
+ * %true if a request was added to the dispatch queue, %false otherwise.
+ */
+static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
+ int error)
+{
+ struct request_queue *q = rq->q;
+ struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
+ bool queued = false;
+
+ BUG_ON(rq->flush.seq & seq);
+ rq->flush.seq |= seq;
+
+ if (likely(!error))
+ seq = blk_flush_cur_seq(rq);
+ else
+ seq = REQ_FSEQ_DONE;
+
+ switch (seq) {
+ case REQ_FSEQ_PREFLUSH:
+ case REQ_FSEQ_POSTFLUSH:
+ /* queue for flush */
+ if (list_empty(pending))
+ q->flush_pending_since = jiffies;
+ list_move_tail(&rq->flush.list, pending);
+ break;

- /* dispatch the next flush if there's one */
- if (!list_empty(&q->pending_flushes)) {
- next_rq = list_entry_rq(q->pending_flushes.next);
- list_move(&next_rq->queuelist, &q->queue_head);
- }
+ case REQ_FSEQ_DATA:
+ list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
+ list_add(&rq->queuelist, &q->queue_head);
+ queued = true;
+ break;
+
+ case REQ_FSEQ_DONE:
+ /*
+ * @rq was previously adjusted by blk_flush_issue() for
+ * flush sequencing and may already have gone through the
+ * flush data request completion path. Restore @rq for
+ * normal completion and end it.
+ */
+ BUG_ON(!list_empty(&rq->queuelist));
+ list_del_init(&rq->flush.list);
+ blk_flush_restore_request(rq);
+ __blk_end_request_all(rq, error);
+ break;
+
+ default:
+ BUG();
}
- return next_rq;
+
+ return blk_kick_flush(q) | queued;
}

-static void blk_flush_complete_seq_end_io(struct request_queue *q,
- unsigned seq, int error)
+static void flush_end_io(struct request *flush_rq, int error)
{
+ struct request_queue *q = flush_rq->q;
+ struct list_head *running = &q->flush_queue[q->flush_running_idx];
bool was_empty = elv_queue_empty(q);
- struct request *next_rq;
+ bool queued = false;
+ struct request *rq, *n;

- next_rq = blk_flush_complete_seq(q, seq, error);
+ BUG_ON(q->flush_pending_idx == q->flush_running_idx);

- /*
- * Moving a request silently to empty queue_head may stall the
- * queue. Kick the queue in those cases.
- */
- if (was_empty && next_rq)
+ /* account completion of the flush request */
+ q->flush_running_idx ^= 1;
+ elv_completed_request(q, flush_rq);
+
+ /* and push the waiting requests to the next stage */
+ list_for_each_entry_safe(rq, n, running, flush.list) {
+ unsigned int seq = blk_flush_cur_seq(rq);
+
+ BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
+ queued |= blk_flush_complete_seq(rq, seq, error);
+ }
+
+ /* after populating an empty queue, kick it to avoid stall */
+ if (queued && was_empty)
__blk_run_queue(q);
}

-static void pre_flush_end_io(struct request *rq, int error)
+/**
+ * blk_kick_flush - consider issuing flush request
+ * @q: request_queue being kicked
+ *
+ * Flush related states of @q have changed, consider issuing flush request.
+ * Please read the comment at the top of this file for more info.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock)
+ *
+ * RETURNS:
+ * %true if flush was issued, %false otherwise.
+ */
+static bool blk_kick_flush(struct request_queue *q)
{
- elv_completed_request(rq->q, rq);
- blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error);
+ struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
+ struct request *first_rq =
+ list_first_entry(pending, struct request, flush.list);
+
+ /* C1 described at the top of this file */
+ if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))
+ return false;
+
+ /* C2 and C3 */
+ if (!list_empty(&q->flush_data_in_flight) &&
+ time_before(jiffies,
+ q->flush_pending_since + FLUSH_PENDING_TIMEOUT))
+ return false;
+
+ /*
+ * Issue flush and toggle pending_idx. This makes pending_idx
+ * different from running_idx, which means flush is in flight.
+ */
+ blk_rq_init(q, &q->flush_rq);
+ q->flush_rq.cmd_type = REQ_TYPE_FS;
+ q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
+ q->flush_rq.rq_disk = first_rq->rq_disk;
+ q->flush_rq.end_io = flush_end_io;
+
+ q->flush_pending_idx ^= 1;
+ elv_insert(q, &q->flush_rq, ELEVATOR_INSERT_FRONT);
+ return true;
}

static void flush_data_end_io(struct request *rq, int error)
{
- elv_completed_request(rq->q, rq);
- blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error);
-}
+ bool was_empty = elv_queue_empty(rq->q);

-static void post_flush_end_io(struct request *rq, int error)
-{
- elv_completed_request(rq->q, rq);
- blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
+ /* after populating an empty queue, kick it to avoid stall */
+ if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error) && was_empty)
+ __blk_run_queue(rq->q);
}

-static void init_flush_request(struct request *rq, struct gendisk *disk)
+/**
+ * blk_insert_flush - insert a new FLUSH/FUA request
+ * @rq: request to insert
+ *
+ * To be called from elv_insert() for %ELEVATOR_INSERT_FLUSH insertions.
+ * @rq is being submitted. Analyze what needs to be done and put it on the
+ * right queue.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock)
+ */
+void blk_insert_flush(struct request *rq)
{
- rq->cmd_type = REQ_TYPE_FS;
- rq->cmd_flags = WRITE_FLUSH;
- rq->rq_disk = disk;
-}
+ struct request_queue *q = rq->q;
+ unsigned int fflags = q->flush_flags; /* may change, cache */
+ unsigned int policy = blk_flush_policy(fflags, rq);

-static struct request *queue_next_fseq(struct request_queue *q)
-{
- struct request *orig_rq = q->orig_flush_rq;
- struct request *rq = &q->flush_rq;
+ BUG_ON(rq->end_io);
+ BUG_ON(!rq->bio || rq->bio != rq->biotail);

- blk_rq_init(q, rq);
+ /*
+ * @policy now records what operations need to be done. Adjust
+ * REQ_FLUSH and FUA for the driver.
+ */
+ rq->cmd_flags &= ~REQ_FLUSH;
+ if (!(fflags & REQ_FUA))
+ rq->cmd_flags &= ~REQ_FUA;

- switch (blk_flush_cur_seq(q)) {
- case QUEUE_FSEQ_PREFLUSH:
- init_flush_request(rq, orig_rq->rq_disk);
- rq->end_io = pre_flush_end_io;
- break;
- case QUEUE_FSEQ_DATA:
- init_request_from_bio(rq, orig_rq->bio);
- /*
- * orig_rq->rq_disk may be different from
- * bio->bi_bdev->bd_disk if orig_rq got here through
- * remapping drivers. Make sure rq->rq_disk points
- * to the same one as orig_rq.
- */
- rq->rq_disk = orig_rq->rq_disk;
- rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
- rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
- rq->end_io = flush_data_end_io;
- break;
- case QUEUE_FSEQ_POSTFLUSH:
- init_flush_request(rq, orig_rq->rq_disk);
- rq->end_io = post_flush_end_io;
- break;
- default:
- BUG();
+ /*
+ * If there's data but flush is not necessary, the request can be
+ * processed directly without going through flush machinery. Queue
+ * for normal execution.
+ */
+ if ((policy & REQ_FSEQ_DATA) &&
+ !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
+ list_add(&rq->queuelist, &q->queue_head);
+ return;
}

- elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
- return rq;
+ /*
+ * @rq should go through flush machinery. Mark it part of flush
+ * sequence and submit for further processing.
+ */
+ memset(&rq->flush, 0, sizeof(rq->flush));
+ INIT_LIST_HEAD(&rq->flush.list);
+ rq->cmd_flags |= REQ_FLUSH_SEQ;
+ rq->end_io = flush_data_end_io;
+
+ blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
}

-struct request *blk_do_flush(struct request_queue *q, struct request *rq)
+/**
+ * blk_abort_flush - @q is being aborted, abort flush requests
+ * @q: request_queue being aborted
+ *
+ * To be called from elv_abort_queue(). @q is being aborted. Prepare all
+ * FLUSH/FUA requests for abortion.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock)
+ */
+void blk_abort_flushes(struct request_queue *q)
{
- unsigned int fflags = q->flush_flags; /* may change, cache it */
- bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA;
- bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH);
- bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA);
- unsigned skip = 0;
+ struct request *rq, *n;
+ int i;

/*
- * Special case. If there's data but flush is not necessary,
- * the request can be issued directly.
- *
- * Flush w/o data should be able to be issued directly too but
- * currently some drivers assume that rq->bio contains
- * non-zero data if it isn't NULL and empty FLUSH requests
- * getting here usually have bio's without data.
+ * Requests in flight for data are already owned by the dispatch
+ * queue or the device driver. Just restore for normal completion.
*/
- if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
- rq->cmd_flags &= ~REQ_FLUSH;
- if (!has_fua)
- rq->cmd_flags &= ~REQ_FUA;
- return rq;
+ list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) {
+ list_del_init(&rq->flush.list);
+ blk_flush_restore_request(rq);
}

/*
- * Sequenced flushes can't be processed in parallel. If
- * another one is already in progress, queue for later
- * processing.
+ * We need to give away requests on flush queues. Restore for
+ * normal completion and put them on the dispatch queue.
*/
- if (q->flush_seq) {
- list_move_tail(&rq->queuelist, &q->pending_flushes);
- return NULL;
+ for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) {
+ list_for_each_entry_safe(rq, n, &q->flush_queue[i],
+ flush.list) {
+ list_del_init(&rq->flush.list);
+ blk_flush_restore_request(rq);
+ list_add_tail(&rq->queuelist, &q->queue_head);
+ }
}
-
- /*
- * Start a new flush sequence
- */
- q->flush_err = 0;
- q->flush_seq |= QUEUE_FSEQ_STARTED;
-
- /* adjust FLUSH/FUA of the original request and stash it away */
- rq->cmd_flags &= ~REQ_FLUSH;
- if (!has_fua)
- rq->cmd_flags &= ~REQ_FUA;
- blk_dequeue_request(rq);
- q->orig_flush_rq = rq;
-
- /* skip unneded sequences and return the first one */
- if (!do_preflush)
- skip |= QUEUE_FSEQ_PREFLUSH;
- if (!blk_rq_sectors(rq))
- skip |= QUEUE_FSEQ_DATA;
- if (!do_postflush)
- skip |= QUEUE_FSEQ_POSTFLUSH;
- return blk_flush_complete_seq(q, skip, 0);
}

static void bio_end_flush(struct bio *bio, int err)
Index: work/block/blk.h
===================================================================
--- work.orig/block/blk.h
+++ work/block/blk.h
@@ -51,21 +51,17 @@ static inline void blk_clear_rq_complete
*/
#define ELV_ON_HASH(rq) (!hlist_unhashed(&(rq)->hash))

-struct request *blk_do_flush(struct request_queue *q, struct request *rq);
+void blk_insert_flush(struct request *rq);
+void blk_abort_flushes(struct request_queue *q);

static inline struct request *__elv_next_request(struct request_queue *q)
{
struct request *rq;

while (1) {
- while (!list_empty(&q->queue_head)) {
+ if (!list_empty(&q->queue_head)) {
rq = list_entry_rq(q->queue_head.next);
- if (!(rq->cmd_flags & (REQ_FLUSH | REQ_FUA)) ||
- rq == &q->flush_rq)
- return rq;
- rq = blk_do_flush(q, rq);
- if (rq)
- return rq;
+ return rq;
}

if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
Index: work/block/elevator.c
===================================================================
--- work.orig/block/elevator.c
+++ work/block/elevator.c
@@ -673,6 +673,11 @@ void elv_insert(struct request_queue *q,
q->elevator->ops->elevator_add_req_fn(q, rq);
break;

+ case ELEVATOR_INSERT_FLUSH:
+ rq->cmd_flags |= REQ_SOFTBARRIER;
+ blk_insert_flush(rq);
+ break;
+
default:
printk(KERN_ERR "%s: bad insertion point %d\n",
__func__, where);
@@ -785,6 +790,8 @@ void elv_abort_queue(struct request_queu
{
struct request *rq;

+ blk_abort_flushes(q);
+
while (!list_empty(&q->queue_head)) {
rq = list_entry_rq(q->queue_head.next);
rq->cmd_flags |= REQ_QUIET;
Index: work/include/linux/elevator.h
===================================================================
--- work.orig/include/linux/elevator.h
+++ work/include/linux/elevator.h
@@ -167,6 +167,7 @@ extern struct request *elv_rb_find(struc
#define ELEVATOR_INSERT_BACK 2
#define ELEVATOR_INSERT_SORT 3
#define ELEVATOR_INSERT_REQUEUE 4
+#define ELEVATOR_INSERT_FLUSH 5

/*
* return values from elevator_may_queue_fn
Index: work/include/linux/blkdev.h
===================================================================
--- work.orig/include/linux/blkdev.h
+++ work/include/linux/blkdev.h
@@ -103,9 +103,15 @@ struct request {
*/
union {
struct rb_node rb_node; /* sort/lookup */
- void *completion_data;
+ struct {
+ unsigned int serial;
+ unsigned int seq;
+ struct list_head list;
+ } flush;
};

+ void *completion_data;
+
/*
* Three pointers are available for the IO schedulers, if they need
* more they have to dynamically allocate it.
@@ -363,11 +369,12 @@ struct request_queue
* for flush operations
*/
unsigned int flush_flags;
- unsigned int flush_seq;
- int flush_err;
+ unsigned int flush_pending_idx:1;
+ unsigned int flush_running_idx:1;
+ unsigned long flush_pending_since;
+ struct list_head flush_queue[2];
+ struct list_head flush_data_in_flight;
struct request flush_rq;
- struct request *orig_flush_rq;
- struct list_head pending_flushes;

struct mutex sysfs_lock;

Index: work/include/linux/blk_types.h
===================================================================
--- work.orig/include/linux/blk_types.h
+++ work/include/linux/blk_types.h
@@ -148,6 +148,7 @@ enum rq_flag_bits {
__REQ_ALLOCED, /* request came from our alloc pool */
__REQ_COPY_USER, /* contains copies of user pages */
__REQ_FLUSH, /* request for cache flush */
+ __REQ_FLUSH_SEQ, /* request for flush sequence */
__REQ_IO_STAT, /* account I/O stat */
__REQ_MIXED_MERGE, /* merge of different types, fail separately */
__REQ_SECURE, /* secure discard (used with __REQ_DISCARD) */
@@ -188,6 +189,7 @@ enum rq_flag_bits {
#define REQ_ALLOCED (1 << __REQ_ALLOCED)
#define REQ_COPY_USER (1 << __REQ_COPY_USER)
#define REQ_FLUSH (1 << __REQ_FLUSH)
+#define REQ_FLUSH_SEQ (1 << __REQ_FLUSH_SEQ)
#define REQ_IO_STAT (1 << __REQ_IO_STAT)
#define REQ_MIXED_MERGE (1 << __REQ_MIXED_MERGE)
#define REQ_SECURE (1 << __REQ_SECURE)

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