From: Joseph Glanville <joseph.glanville@orionvm.com.au>
To: Tejun Heo <tj@kernel.org>
Cc: NeilBrown <neilb@suse.de>,
Kent Overstreet <koverstreet@google.com>,
Jens Axboe <axboe@kernel.dk>,
Philipp Reisner <philipp.reisner@linbit.com>,
linux-kernel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Vivek Goyal <vgoyal@redhat.com>,
drbd-dev@lists.linbit.com
Subject: Re: [Drbd-dev] FLUSH/FUA documentation & code discrepancy
Date: Thu, 13 Sep 2012 10:17:35 +1000 [thread overview]
Message-ID: <CAOzFzEhU6Y2hbRKU9qdFbtx_A-+wgs14E8Xza107G+z7uHzs_w@mail.gmail.com> (raw)
In-Reply-To: <CAOzFzEhfoCpGCy0n5cu60xz+tSbB26g1f2ztcD1DwZOY-6aTwQ@mail.gmail.com>
On 13 September 2012 09:53, Joseph Glanville
<joseph.glanville@orionvm.com.au> wrote:
> On 13 September 2012 09:20, Tejun Heo <tj@kernel.org> wrote:
>> On Thu, Sep 13, 2012 at 09:12:25AM +1000, Joseph Glanville wrote:
>>> diff --git a/block/blk-core.c b/block/blk-core.c
>>> index 4b4dbdf..68b5671 100644
>>> --- a/block/blk-core.c
>>> +++ b/block/blk-core.c
>>> @@ -1809,6 +1809,9 @@ EXPORT_SYMBOL(generic_make_request);
>>> * uses that function to do most of the work. Both are fairly rough
>>> * interfaces; @bio must be presetup and ready for I/O.
>>> *
>>> + * Ordering of requests is not guaranteed, callers should drain the queue
>>> + * and issue a flush before submission of any dependent bios.
>>
>> I think using "requests" here is confusing given that struct request
>> means something else in the block layer. Also, the caller doesn't
>
> Agreed, my bad.
>
>> have to drain the whole queue but just the ones involved in the
>> dependency and flush doesn't really matter here although mentioning
>> that flush too doesn't have any ordering guarantee would be nice.
>
> Will do.
> Would you prefer it being added to the top of the file describing the
> semantics or the blkdev_issue_flush function itself?
>
>> Also, updating submit_bio() comment too would be nice - something
>> simple about lack of ordering and then reference to
>> generic_make_request().
>
> Will do.
>
>>
>> Thanks.
>>
>> --
>> tejun
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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>> Please read the FAQ at http://www.tux.org/lkml/
>
>
>
> --
> CTO | Orion Virtualisation Solutions | www.orionvm.com.au
> Phone: 1300 56 99 52 | Mobile: 0428 754 846
diff --git a/block/blk-core.c b/block/blk-core.c
index 4b4dbdf..b3559d8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1749,6 +1749,11 @@ end_io:
* bio happens to be merged with someone else, and may resubmit the bio to
* a lower device by calling into generic_make_request recursively, which
* means the bio should NOT be touched after the call to ->make_request_fn.
+ *
+ * Ordering is not guaranteed, callers of generic_make_request()
+ * that require ordering should ensure dependencies are first drained
+ * before submission of dependent bios.
+ *
*/
void generic_make_request(struct bio *bio)
{
@@ -1808,6 +1813,7 @@ EXPORT_SYMBOL(generic_make_request);
* submit_bio() is very similar in purpose to generic_make_request(), and
* uses that function to do most of the work. Both are fairly rough
* interfaces; @bio must be presetup and ready for I/O.
+ * Note: submit_bio() doesn't ensure ordering, see generic_make_request()
*
*/
void submit_bio(int rw, struct bio *bio)
--
CTO | Orion Virtualisation Solutions | www.orionvm.com.au
Phone: 1300 56 99 52 | Mobile: 0428 754 846
next prev parent reply other threads:[~2012-09-13 0:17 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-04 12:32 FLUSH/FUA documentation & code discrepancy Philipp Reisner
2012-09-04 22:46 ` Tejun Heo
2012-09-05 8:44 ` [Drbd-dev] " Philipp Reisner
2012-09-05 8:49 ` Tejun Heo
2012-09-05 10:07 ` Lars Ellenberg
2012-09-06 21:29 ` Tejun Heo
2012-09-07 8:42 ` Lars Ellenberg
2012-09-10 22:54 ` Tejun Heo
2012-09-10 23:06 ` Tejun Heo
2012-09-10 23:12 ` Kent Overstreet
2012-09-10 23:31 ` Kent Overstreet
2012-09-11 5:58 ` NeilBrown
2012-09-11 8:25 ` Lars Ellenberg
2012-09-11 14:41 ` Vivek Goyal
2012-09-12 18:58 ` Tejun Heo
2012-09-12 23:12 ` Joseph Glanville
2012-09-12 23:20 ` Tejun Heo
2012-09-12 23:53 ` Joseph Glanville
2012-09-13 0:17 ` Joseph Glanville [this message]
2012-09-13 3:10 ` Joseph Glanville
2012-09-13 19:25 ` Tejun Heo
2012-09-11 14:34 ` Vivek Goyal
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