Re: [PATCH v7 3/3] bio: add limit_bio_size sysfs

[Changheun Lee]

> On Tue, Apr 13, 2021 at 11:55:02AM +0900, Changheun Lee wrote:
> > Add limit_bio_size block sysfs node to limit bio size.
> > Queue flag QUEUE_FLAG_LIMIT_BIO_SIZE will be set if limit_bio_size is set.
> > And bio max size will be limited by queue max sectors via
> > QUEUE_FLAG_LIMIT_BIO_SIZE set.
> > 
> > Signed-off-by: Changheun Lee 
> > ---
> >  Documentation/ABI/testing/sysfs-block | 10 ++
> >  Documentation/block/queue-sysfs.rst   |  7 +++
> >  block/blk-sysfs.c |  3 +++
> >  3 files changed, 20 insertions(+)
> 
> Isn't it too late to change the sysfs entry after the device has been
> probed and initialized by the kernel as the kernel does not look at this
> value after that?

Kernel will take a look this when page is merged to bio. And bio size will
be limited dynamically.

> 
> Why do you need a userspace knob for this?  What tool is going to ever
> change this, and what logic is it going to use to change it?  Why can't
> the kernel also just "do the right thing" and properly detect this
> option as well as userspace can?

Actually I didn't considerate userspace knob at first. And there is no tool,
no logic to change it. It's a kind of policy about bio max size.
One time setting will be OK on system boot time actually.

At the first, I suggested 1MB bio max size. It is same with bio max size
before applying of multipage bvec. But there are requests of big bio size
on another system environment, and feedback of knob for utility too.
So I made this as a optional for each system, and a knob too.

> 
> thanks,
> 
> greg k-h


Thanks,

Changheun Lee

Re: [PATCH v7 3/3] bio: add limit_bio_size sysfs

[Greg KH]

On Tue, Apr 13, 2021 at 11:55:02AM +0900, Changheun Lee wrote:
> Add limit_bio_size block sysfs node to limit bio size.
> Queue flag QUEUE_FLAG_LIMIT_BIO_SIZE will be set if limit_bio_size is set.
> And bio max size will be limited by queue max sectors via
> QUEUE_FLAG_LIMIT_BIO_SIZE set.
> 
> Signed-off-by: Changheun Lee 
> ---
>  Documentation/ABI/testing/sysfs-block | 10 ++
>  Documentation/block/queue-sysfs.rst   |  7 +++
>  block/blk-sysfs.c |  3 +++
>  3 files changed, 20 insertions(+)

Isn't it too late to change the sysfs entry after the device has been
probed and initialized by the kernel as the kernel does not look at this
value after that?

Why do you need a userspace knob for this?  What tool is going to ever
change this, and what logic is it going to use to change it?  Why can't
the kernel also just "do the right thing" and properly detect this
option as well as userspace can?

thanks,

greg k-h

[PATCH v7 3/3] bio: add limit_bio_size sysfs

[Changheun Lee]

Add limit_bio_size block sysfs node to limit bio size.
Queue flag QUEUE_FLAG_LIMIT_BIO_SIZE will be set if limit_bio_size is set.
And bio max size will be limited by queue max sectors via
QUEUE_FLAG_LIMIT_BIO_SIZE set.

Signed-off-by: Changheun Lee 
---
 Documentation/ABI/testing/sysfs-block | 10 ++
 Documentation/block/queue-sysfs.rst   |  7 +++
 block/blk-sysfs.c |  3 +++
 3 files changed, 20 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-block 
b/Documentation/ABI/testing/sysfs-block
index e34cdeeeb9d4..86a7b15410cf 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -316,3 +316,13 @@ Description:
does not complete in this time then the block driver timeout
handler is invoked. That timeout handler can decide to retry
the request, to fail it or to start a device recovery strategy.
+
+What:  /sys/block//queue/limit_bio_size
+Date:  Feb, 2021
+Contact:   Changheun Lee 
+Description:
+   (RW) Toggle for set/clear QUEUE_FLAG_LIMIT_BIO_SIZE queue flag.
+   Queue flag QUEUE_FLAG_LIMIT_BIO_SIZE will be set if 
limit_bio_size
+   is set. And bio max size will be limited by queue max sectors.
+   QUEUE_FLAG_LIMIT_BIO_SIZE will be cleared if limit_bio_size is
+   cleard. And limit of bio max size will be cleard.
diff --git a/Documentation/block/queue-sysfs.rst 
b/Documentation/block/queue-sysfs.rst
index 4dc7f0d499a8..220d183a4c11 100644
--- a/Documentation/block/queue-sysfs.rst
+++ b/Documentation/block/queue-sysfs.rst
@@ -286,4 +286,11 @@ sequential zones of zoned block devices (devices with a 
zoned attributed
 that reports "host-managed" or "host-aware"). This value is always 0 for
 regular block devices.
 
+limit_bio_size (RW)
+---
+This indicates QUEUE_FLAG_LIMIT_BIO_SIZE queue flag value. And
+QUEUE_FLAG_LIMIT_BIO_SIZE can be changed via set(1)/clear(0) this node.
+bio max size will be limited by queue max sectors via set this node. And
+limit of bio max size will be cleard via clear this node.
+
 Jens Axboe , February 2009
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 0f4f0c8a7825..4625d5319daf 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -294,6 +294,7 @@ QUEUE_SYSFS_BIT_FNS(nonrot, NONROT, 1);
 QUEUE_SYSFS_BIT_FNS(random, ADD_RANDOM, 0);
 QUEUE_SYSFS_BIT_FNS(iostats, IO_STAT, 0);
 QUEUE_SYSFS_BIT_FNS(stable_writes, STABLE_WRITES, 0);
+QUEUE_SYSFS_BIT_FNS(limit_bio_size, LIMIT_BIO_SIZE, 0);
 #undef QUEUE_SYSFS_BIT_FNS
 
 static ssize_t queue_zoned_show(struct request_queue *q, char *page)
@@ -625,6 +626,7 @@ QUEUE_RW_ENTRY(queue_nonrot, "rotational");
 QUEUE_RW_ENTRY(queue_iostats, "iostats");
 QUEUE_RW_ENTRY(queue_random, "add_random");
 QUEUE_RW_ENTRY(queue_stable_writes, "stable_writes");
+QUEUE_RW_ENTRY(queue_limit_bio_size, "limit_bio_size");
 
 static struct attribute *queue_attrs[] = {
_requests_entry.attr,
@@ -659,6 +661,7 @@ static struct attribute *queue_attrs[] = {
_rq_affinity_entry.attr,
_iostats_entry.attr,
_stable_writes_entry.attr,
+   _limit_bio_size_entry.attr,
_random_entry.attr,
_poll_entry.attr,
_wc_entry.attr,
-- 
2.29.0