Hello,
Regarding the QUEUE_FLAG_STANDBY_EN flag, it is like what you added.
However I find some problems with the code, see my comments below.
-----Original Message-----
From: Alexander Atanasov <alexander.atana...@virtuozzo.com>
Date: Tuesday, 18 October 2022 at 5:41 PM
To: Kui Liu <kui....@acronis.com>, Konstantin Khorenko
<khore...@virtuozzo.com>, Alexey Kuznetsov <kuz...@acronis.com>
Cc: Devel <devel@openvz.org>
Subject: Re: [Devel] [PATCH RH9] dm-ploop: port the standby mode feature.
On 18.10.22 12:34, Alexander Atanasov wrote:
> Hi,
>
> On 18.10.22 9:13, Kui Liu wrote:
>> Hi, all
>>
>> How about we introduce another block queue flag, say
>> QUEUE_FLAG_STANDBY_EN, to indicate whether
>> the device support the standby mode. the flag bit shall be set by SCST
>> when a blockio device is created, if
>> the blockio device is ploop device, then it will turn on standby mode
>> check in ploop, if the blockio
>> device is not ploop device, it should have no impact at all.
>>
>> As for ploop not being used by scst, the flag is always 0, so we can
>> skip standby mode check in ploop by checking
>> the flag at beginning of 'check_standby_mode()'.
>>
>> How do you think of above implementation?
Something like this ?
Sorry for the attachment . Added check for blk_queue_standby_en in
ploop_check_standby_mode.
--
Regards,
Alexander Atanasov
diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index e8288e522e28..a247eb169b32 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -19,6 +19,7 @@
#include <uapi/linux/falloc.h>
#include "dm-ploop.h"
#include "dm-rq.h"
+#include "dm-core.h"
#define PREALLOC_SIZE (128ULL * 1024 * 1024)
@@ -28,6 +29,8 @@ static void ploop_prq_endio(struct pio *pio, void
*prq_ptr,
#define DM_MSG_PREFIX "ploop"
+DEFINE_STATIC_KEY_FALSE(ploop_standby_check);
+
static unsigned int ploop_pio_nr_segs(struct pio *pio)
{
struct bvec_iter bi = {
@@ -1163,6 +1166,26 @@ static void ploop_queue_resubmit(struct pio *pio)
queue_work(ploop->wq, &ploop->worker);
}
+static void ploop_check_standby_mode(struct ploop *ploop, long res) {
+ struct request_queue *q = ploop_blk_queue(ploop);
+ int prev;
+
+ if (!blk_queue_standby_en(q))
+ return;
+
+ /* move to standby if delta lease was stolen or mount is gone */
+ if (res != -EBUSY && res != -ENOTCONN && res != -EIO) {
+ return;
+ }
+
+ spin_lock_irq(&q->queue_lock);
+ prev = blk_queue_flag_test_and_set(QUEUE_FLAG_STANDBY, q);
+ spin_unlock_irq(&q->queue_lock);
+
+ if (!prev)
+ pr_info("ploop: switch into standby mode\n");
+}
+
static void ploop_data_rw_complete(struct pio *pio)
{
bool completed;
@@ -1175,6 +1198,8 @@ static void ploop_data_rw_complete(struct pio *pio)
ploop_queue_resubmit(pio);
return;
}
+ if (!static_branch_unlikely(&ploop_standby_check))
+ ploop_check_standby_mode(pio->ploop, pio->ret);
pio->bi_status = errno_to_blk_status(pio->ret);
}
[LIU]: if(!static_branch_unlikely(&ploop_standby_check)) or if
(static_branch_unlikely(&ploop_standby_check))?
In ploop_clone_and_map(), it is "if
(static_branch_unlikely(&ploop_standby_check)", which I think is correct one.
@@ -1815,8 +1840,11 @@ void do_ploop_fsync_work(struct work_struct *ws)
ret = vfs_fsync(file, 0);
while ((pio = ploop_pio_list_pop(&flush_pios)) != NULL) {
- if (unlikely(ret))
+ if (unlikely(ret)) {
pio->bi_status = errno_to_blk_status(ret);
+ if (!static_branch_unlikely(&ploop_standby_check))
+ ploop_check_standby_mode(ploop, ret);
+ }
ploop_pio_endio(pio);
}
}
[LIU]: Same here, if (!static_branch_unlikely(&ploop_standby_check) or if
(static_branch_unlikely(&ploop_standby_check)?
@@ -1869,6 +1897,12 @@ int ploop_clone_and_map(struct dm_target *ti,
struct request *rq,
struct ploop_rq *prq;
struct pio *pio;
+
+ if (static_branch_unlikely(&ploop_standby_check)) {
+ if (blk_queue_standby(ploop_blk_queue(ploop)))
+ return DM_MAPIO_KILL;
+ }
+
if (blk_rq_bytes(rq) && ploop_rq_valid(ploop, rq) < 0)
return DM_MAPIO_KILL;
diff --git a/drivers/md/dm-ploop-target.c b/drivers/md/dm-ploop-target.c
index 4f7dc36eee0c..dda0fe957c1f 100644
--- a/drivers/md/dm-ploop-target.c
+++ b/drivers/md/dm-ploop-target.c
@@ -21,6 +21,7 @@
#include <linux/uio.h>
#include <linux/error-injection.h>
#include "dm-ploop.h"
+#include "dm-core.h"
#define DM_MSG_PREFIX "ploop"
@@ -32,6 +33,7 @@ MODULE_PARM_DESC(ignore_signature_disk_in_use,
static struct kmem_cache *prq_cache;
static struct kmem_cache *pio_cache;
struct kmem_cache *cow_cache;
+extern struct static_key ploop_standby_check;
static void ploop_aio_do_completion(struct pio *pio)
{
@@ -406,6 +408,14 @@ static int ploop_ctr(struct dm_target *ti, unsigned
int argc, char **argv)
ti->private = ploop;
ploop->ti = ti;
+ if (blk_queue_standby_en(ploop_blk_queue(ploop))) {
+ blk_queue_flag_clear(QUEUE_FLAG_STANDBY,
ploop_blk_queue(ploop));
+ if (!static_key_enabled(&ploop_standby_check)) {
+ static_key_enable(&ploop_standby_check);
+ pr_info("ploop: standby mode check enabled\n");
+ }
+ }
+
[LIU]: This may not work, because normally a ploop device is created first
before being attached to SCST, which means 'ploop_ctr' is called before
QUEUE_FLAG_STANDBY_EN can be set. We need to put "
static_key_enable(&ploop_standby_check))" somewhere else.
if (kstrtou32(argv[0], 10, &ploop->cluster_log) < 0) {
ret = -EINVAL;
ti->error = "could not parse cluster_log";
diff --git a/drivers/md/dm-ploop.h b/drivers/md/dm-ploop.h
index 5d953278a976..f7c21b0b1597 100644
--- a/drivers/md/dm-ploop.h
+++ b/drivers/md/dm-ploop.h
@@ -230,6 +230,7 @@ struct ploop {
struct timer_list enospc_timer;
bool event_enospc;
};
+#define ploop_blk_queue(p) ((p)->ti->table->md->queue)
struct ploop_rq {
struct request *rq;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8fcd753c70b0..8928161e5b1d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -434,6 +434,8 @@ struct request_queue {
#define QUEUE_FLAG_RQ_ALLOC_TIME 27 /* record rq->alloc_time_ns */
#define QUEUE_FLAG_HCTX_ACTIVE 28 /* at least one blk-mq hctx is
active */
#define QUEUE_FLAG_NOWAIT 29 /* device supports NOWAIT */
+#define QUEUE_FLAG_STANDBY 30 /* unable to handle read/write
requests */
+#define QUEUE_FLAG_STANDBY_EN 30 /* enable standby queue flag */
[LIU]: Should use a different number for QUEUE_FLAG_STANDBY_EN.
#define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) |
\
(1 << QUEUE_FLAG_SAME_COMP) | \
@@ -480,6 +482,8 @@ bool blk_queue_flag_test_and_set(unsigned int flag,
struct request_queue *q);
#define blk_queue_fua(q) test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags)
#define blk_queue_registered(q) test_bit(QUEUE_FLAG_REGISTERED,
&(q)->queue_flags)
#define blk_queue_nowait(q) test_bit(QUEUE_FLAG_NOWAIT,
&(q)->queue_flags)
+#define blk_queue_standby(q) test_bit(QUEUE_FLAG_STANDBY,
&(q)->queue_flags)
+#define blk_queue_standby_en(q) test_bit(QUEUE_FLAG_STANDBY_EN,
&(q)->queue_flags)
extern void blk_set_pm_only(struct request_queue *q);
extern void blk_clear_pm_only(struct request_queue *q);
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