>From c034a8b69ecc13ef924edd342ff945f890ebac61 Mon Sep 17 00:00:00 2001
From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Date: Tue, 14 Jul 2009 12:58:34 +0300
Subject: [PATCH] HACK: do I/O read requests while ext3 journal recovers
The ext3 journal can take a long time to recover at mount
time. That was partially fixed by placing a barrier into
the I/O queue and then not waiting for the actual I/O to
complete.
However the barrier stops all other I/O, making the file
system unresponsive until the journal I/O completes
anyway.
This hack allows I/O read requests to jump the barrier
to the front on the I/O queue.
Note that the hack only takes affect while the ext3 journal
is recovering.
Note also, that in the normal situation, the I/O scheduler
is entitled to reorder I/O requests however it pleases,
so jumping read requests to the front is quite valid.
Where the normal rules are being broken, is that a barrier
is being jumped over. That is safe for two reasons:
- barriers are not otherwise used by ext3, vfat or swap
- ext3 I/O all goes through buffers, so any attempt
to read from sectors not yet written, will successfully
read from the buffers instead.
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
block/blk-core.c | 121 ++++++++++++++++++++++++++++++++++++++++++-
block/elevator.c | 37 +++++++++++++
fs/buffer.c | 9 +++-
fs/ext3/super.c | 8 +++
fs/jbd/journal.c | 8 +++
include/linux/bio.h | 3 +
include/linux/blkdev.h | 12 ++++
include/linux/buffer_head.h | 2 +
include/linux/elevator.h | 1 +
include/linux/fs.h | 1 +
10 files changed, 199 insertions(+), 3 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index c36aa98..66ac9b5 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1003,6 +1003,23 @@ static inline void add_request(struct request_queue *q, struct request *req)
__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
}
+/*
+ * Leapfrog requests are inserted with a special 'where' code:
+ * ELEVATOR_INSERT_FRONT_BACK which means the back of the READ requests that
+ * are at the front of the dispatch queue.
+ */
+static inline void request_leapfrog(struct request_queue *q,
+ struct request *req)
+{
+ drive_stat_acct(req, 1);
+
+ /*
+ * elevator indicated where it wants this request to be
+ * inserted at elevator_merge time
+ */
+ __elv_add_request(q, req, ELEVATOR_INSERT_FRONT_BACK, 0);
+}
+
static void part_round_stats_single(int cpu, struct hd_struct *part,
unsigned long now)
{
@@ -1117,6 +1134,13 @@ void init_request_from_bio(struct request *req, struct bio *bio)
if (bio_rw_meta(bio))
req->cmd_flags |= REQ_RW_META;
+ /*
+ * The bio says to start leapfrog mode, so set the request
+ * to say the same.
+ */
+ if (bio_leapfrog(bio))
+ req->cmd_flags |= REQ_LEAPFROG;
+
req->errors = 0;
req->hard_sector = req->sector = bio->bi_sector;
req->ioprio = bio_prio(bio);
@@ -1124,13 +1148,68 @@ void init_request_from_bio(struct request *req, struct bio *bio)
blk_rq_bio_prep(req->q, req, bio);
}
+/*
+ * This is the same as elv_rq_merge_ok but for leapfrog mode, we are
+ * merging into the dispatch queue and do not want to involve the
+ * I/O scheduler in any way.
+ */
+static int elv_rq_leapfrog_merge_ok(struct request *rq, struct bio *bio)
+{
+ if (!rq_mergeable(rq))
+ return 0;
+
+ /*
+ * Don't merge file system requests and discard requests
+ */
+ if (bio_discard(bio) != bio_discard(rq->bio))
+ return 0;
+
+ /*
+ * different data direction or already started, don't merge
+ */
+ if (bio_data_dir(bio) != rq_data_dir(rq))
+ return 0;
+
+ /*
+ * must be same device and not a special request
+ */
+ if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
+ return 0;
+
+ /*
+ * only merge integrity protected bio into ditto rq
+ */
+ if (bio_integrity(bio) != blk_integrity_rq(rq))
+ return 0;
+
+ return 1;
+}
+
+/* This is the same as elv_try_merge but calls elv_rq_leapfrog_merge_ok */
+static inline int elv_try_leapfrog_merge(struct request *__rq, struct bio *bio)
+{
+ int ret = ELEVATOR_NO_MERGE;
+
+ /*
+ * we can merge and sequence is ok, check if it's possible
+ */
+ if (elv_rq_leapfrog_merge_ok(__rq, bio)) {
+ if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
+ ret = ELEVATOR_BACK_MERGE;
+ else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
+ ret = ELEVATOR_FRONT_MERGE;
+ }
+
+ return ret;
+}
+
static int __make_request(struct request_queue *q, struct bio *bio)
{
struct request *req;
int el_ret, nr_sectors, barrier, discard, err;
const unsigned short prio = bio_prio(bio);
const int sync = bio_sync(bio);
- int rw_flags;
+ int rw_flags, leapfrog = 0;
nr_sectors = bio_sectors(bio);
@@ -1159,6 +1238,40 @@ static int __make_request(struct request_queue *q, struct bio *bio)
if (unlikely(barrier) || elv_queue_empty(q))
goto get_rq;
+ /*
+ * If the request queue is in leapfrog mode, leapfrog READs to the
+ * front of the queue.
+ */
+ if (unlikely(q->leapfrog) && !discard && (bio->bi_rw & (1 << BIO_RW)) == READ) {
+ /* Look in the dispatch queue for a request to merge with */
+ list_for_each_entry(req, &q->queue_head, queuelist) {
+ if (req->cmd_flags & REQ_STARTED)
+ continue;
+ if (rq_data_dir(req) == READ) {
+ /* Try to merge bio into request */
+ el_ret = elv_try_leapfrog_merge(req, bio);
+ /* Front merges are uncommon, so just do back merges */
+ if (el_ret == ELEVATOR_BACK_MERGE && ll_back_merge_fn(q, req, bio)) {
+ /* Merge is OK so plonk bio into this request and we are done */
+ blk_add_trace_bio(q, bio, BLK_TA_BACKMERGE);
+ req->biotail->bi_next = bio;
+ req->biotail = bio;
+ req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+ req->ioprio = ioprio_best(req->ioprio, prio);
+ if (!blk_rq_cpu_valid(req))
+ req->cpu = bio->bi_comp_cpu;
+ drive_stat_acct(req, 0);
+ goto out;
+ }
+ continue;
+ }
+ break;
+ }
+ /* Was not able to merge so create a new request */
+ leapfrog = 1;
+ goto get_rq;
+ }
+
el_ret = elv_merge(q, &req, bio);
switch (el_ret) {
case ELEVATOR_BACK_MERGE:
@@ -1244,7 +1357,11 @@ get_rq:
req->cpu = blk_cpu_to_group(smp_processor_id());
if (elv_queue_empty(q))
blk_plug_device(q);
- add_request(q, req);
+ /* Leapfrogging requests are added specially */
+ if (unlikely(leapfrog))
+ request_leapfrog(q, req);
+ else
+ add_request(q, req);
out:
if (sync)
__generic_unplug_device(q);
diff --git a/block/elevator.c b/block/elevator.c
index a6951f7..80dbd18 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -663,6 +663,31 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
list_add_tail(&rq->queuelist, pos);
break;
+ case ELEVATOR_INSERT_FRONT_BACK:
+ /*
+ * New 'where' code for leapfrog mode. Put the request at the
+ * front of the queue but after any requests that have already
+ * started, and after other READ requests.
+ */
+ {
+ struct request *r;
+ struct list_head *p = &q->queue_head;
+
+ list_for_each_entry(r, &q->queue_head, queuelist) {
+ if (r->cmd_flags & REQ_STARTED) {
+ p = &r->queuelist;
+ continue;
+ }
+ if (rq_data_dir(r) == READ) {
+ p = &r->queuelist;
+ continue;
+ }
+ break;
+ }
+ list_add(&rq->queuelist, p);
+ break;
+ }
+
default:
printk(KERN_ERR "%s: bad insertion point %d\n",
__func__, where);
@@ -691,6 +716,10 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where,
if (blk_barrier_rq(rq))
q->ordcolor ^= 1;
+ /* A request marked as 'leapfrog' cause leapfrog mode to start */
+ if (blk_leapfrog_rq(rq))
+ q->leapfrog += 1;
+
/*
* barriers implicitly indicate back insertion
*/
@@ -773,6 +802,14 @@ struct request *elv_next_request(struct request_queue *q)
*/
rq->cmd_flags |= REQ_STARTED;
blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
+
+ /*
+ * If this request started leapfrog mode, then
+ * leapfrog mode stops now that this request is
+ * starting.
+ */
+ if (blk_leapfrog_rq(rq))
+ q->leapfrog -= 1;
}
if (!q->boundary_rq || q->boundary_rq == rq) {
diff --git a/fs/buffer.c b/fs/buffer.c
index 10179cf..b4f3b92 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2930,8 +2930,15 @@ int submit_bh(int rw, struct buffer_head * bh)
* Mask in barrier bit for a write (could be either a WRITE or a
* WRITE_SYNC
*/
- if (buffer_ordered(bh) && (rw & WRITE))
+ if (buffer_ordered(bh) && (rw & WRITE)) {
rw |= WRITE_BARRIER;
+ /*
+ * If the buffer says to start leapfrog mode, then flag it
+ * on the bio too.
+ */
+ if (buffer_leapfrog(bh))
+ rw |= LEAPFROG;
+ }
/*
* Only clear out a write error when rewriting
diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 59efefb..b75a825 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -2317,8 +2317,16 @@ static void ext3_commit_super (struct super_block * sb,
* write will not reach the disk before any previous ones,
* and we will not have to wait for it either.
*/
+ /*
+ * Start leapfrog mode. Leapfrog mode continues until the
+ * associated I/O request is started by the underlying
+ * block driver. Note that the request is also a barrier
+ * so it is never merged with another request.
+ */
set_buffer_ordered(sbh);
+ set_buffer_leapfrog(sbh);
ll_rw_block(SWRITE, 1, &sbh);
+ clear_buffer_leapfrog(sbh);
clear_buffer_ordered(sbh);
} else if (sync)
sync_dirty_buffer(sbh);
diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index 3fd14ef..5e3628c 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -963,8 +963,16 @@ void journal_update_superblock(journal_t *journal, int wait)
if (wait)
sync_dirty_buffer(bh);
else {
+ /*
+ * Start leapfrog mode. Leapfrog mode continues until the
+ * associated I/O request is started by the underlying
+ * block driver. Note that the request is also a barrier
+ * so it is never merged with another request.
+ */
set_buffer_ordered(bh);
+ set_buffer_leapfrog(bh);
ll_rw_block(SWRITE, 1, &bh);
+ clear_buffer_leapfrog(bh);
clear_buffer_ordered(bh);
}
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 6a64209..43bd58d 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -150,6 +150,7 @@ struct bio {
* bit 7 -- fail fast transport errors
* bit 8 -- fail fast driver errors
* Don't want driver retries for any fast fail whatever the reason.
+ * bit 9 -- start leapfrog mode
*/
#define BIO_RW 0 /* Must match RW in req flags (blkdev.h) */
#define BIO_RW_AHEAD 1 /* Must match FAILFAST in req flags */
@@ -160,6 +161,7 @@ struct bio {
#define BIO_RW_FAILFAST_DEV 6
#define BIO_RW_FAILFAST_TRANSPORT 7
#define BIO_RW_FAILFAST_DRIVER 8
+#define BIO_RW_LEAPFROG 9
/*
* upper 16 bits of bi_rw define the io priority of this bio
@@ -194,6 +196,7 @@ struct bio {
#define bio_rw_meta(bio) ((bio)->bi_rw & (1 << BIO_RW_META))
#define bio_discard(bio) ((bio)->bi_rw & (1 << BIO_RW_DISCARD))
#define bio_empty_barrier(bio) (bio_barrier(bio) && !bio_has_data(bio) && !bio_discard(bio))
+#define bio_leapfrog(bio) ((bio)->bi_rw & (1 << BIO_RW_LEAPFROG))
static inline unsigned int bio_cur_sectors(struct bio *bio)
{
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 031a315..3ed0639 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -109,6 +109,7 @@ enum rq_flag_bits {
__REQ_RW_META, /* metadata io request */
__REQ_COPY_USER, /* contains copies of user pages */
__REQ_INTEGRITY, /* integrity metadata has been remapped */
+ __REQ_LEAPFROG, /* start leapfrog mode */
__REQ_NR_BITS, /* stops here */
};
@@ -135,6 +136,7 @@ enum rq_flag_bits {
#define REQ_RW_META (1 << __REQ_RW_META)
#define REQ_COPY_USER (1 << __REQ_COPY_USER)
#define REQ_INTEGRITY (1 << __REQ_INTEGRITY)
+#define REQ_LEAPFROG (1 << __REQ_LEAPFROG)
#define BLK_MAX_CDB 16
@@ -399,6 +401,15 @@ struct request_queue
unsigned int dma_pad_mask;
unsigned int dma_alignment;
+ /*
+ * Flag indicating leapfrog mode. When a request also
+ * has a leapfrog flag, then the request queue starts
+ * leapfrog mode. When that request is finally started,
+ * leapfrog mode ends. Here 'leapfrog' is a counter, so
+ * if 2 requests start leapfrog mode, then the value is 2.
+ */
+ unsigned int leapfrog;
+
struct blk_queue_tag *queue_tags;
struct list_head tag_busy_list;
@@ -584,6 +595,7 @@ enum {
#define blk_barrier_rq(rq) ((rq)->cmd_flags & REQ_HARDBARRIER)
#define blk_fua_rq(rq) ((rq)->cmd_flags & REQ_FUA)
#define blk_discard_rq(rq) ((rq)->cmd_flags & REQ_DISCARD)
+#define blk_leapfrog_rq(rq) ((rq)->cmd_flags & REQ_LEAPFROG)
#define blk_bidi_rq(rq) ((rq)->next_rq != NULL)
#define blk_empty_barrier(rq) (blk_barrier_rq(rq) && blk_fs_request(rq) && !(rq)->hard_nr_sectors)
/* rq->queuelist of dequeued request must be list_empty() */
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 3ce64b9..2b73a1f 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -35,6 +35,7 @@ enum bh_state_bits {
BH_Ordered, /* ordered write */
BH_Eopnotsupp, /* operation not supported (barrier) */
BH_Unwritten, /* Buffer is allocated on disk but not written */
+ BH_Leapfrog, /* Start leapfrog mode */
BH_PrivateStart,/* not a state bit, but the first bit available
* for private allocation by other entities
@@ -127,6 +128,7 @@ BUFFER_FNS(Write_EIO, write_io_error)
BUFFER_FNS(Ordered, ordered)
BUFFER_FNS(Eopnotsupp, eopnotsupp)
BUFFER_FNS(Unwritten, unwritten)
+BUFFER_FNS(Leapfrog, leapfrog)
#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
#define touch_buffer(bh) mark_page_accessed(bh->b_page)
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 92f6f63..e5112c4 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -160,6 +160,7 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t);
#define ELEVATOR_INSERT_BACK 2
#define ELEVATOR_INSERT_SORT 3
#define ELEVATOR_INSERT_REQUEUE 4
+#define ELEVATOR_INSERT_FRONT_BACK 5
/*
* return values from elevator_may_queue_fn
diff --git a/include/linux/fs.h b/include/linux/fs.h
index aaa6291..1635a41 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -95,6 +95,7 @@ extern int dir_notify_enable;
#define WRITE_BARRIER (WRITE | (1 << BIO_RW_BARRIER))
#define DISCARD_NOBARRIER (1 << BIO_RW_DISCARD)
#define DISCARD_BARRIER ((1 << BIO_RW_DISCARD) | (1 << BIO_RW_BARRIER))
+#define LEAPFROG (1 << BIO_RW_LEAPFROG)
#define SEL_IN 1
#define SEL_OUT 2
--
1.5.6.3
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