From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: Shaohua Li <shli@kernel.org>
Cc: linux-block@vger.kernel.org, axboe@kernel.dk
Subject: Re: [PATCH v2 0/9] Nowait support for stacked block devices
Date: Fri, 6 Oct 2017 07:01:19 -0500 [thread overview]
Message-ID: <0bf484f7-1e95-86c4-c00d-125e22f73a8d@suse.de> (raw)
In-Reply-To: <20171005171938.hob45bzeebvaigu2@kernel.org>
On 10/05/2017 12:19 PM, Shaohua Li wrote:
> On Wed, Oct 04, 2017 at 08:55:02AM -0500, Goldwyn Rodrigues wrote:
>> This is a continuation of the nowait support which was incorporated
>> a while back. We introduced REQ_NOWAIT which would return immediately
>> if the call would block at the block layer. Request based-devices
>> do not wait. However, bio based devices (the ones which exclusively
>> call make_request_fn) need to be trained to handle REQ_NOWAIT.
>>
>> This effort covers the devices under MD and DM which would block
>> for any reason. If there should be more devices or situations
>> which need to be covered, please let me know.
>>
>> The problem with partial writes discussed during v1 turned out
>> to be a bug in partial writes during direct I/O and is fixed
>> by the submitted patch[1].
>>
>> Changes since v1:
>> - mddev to return early in case the device is suspended, within the md code as opposed to ->make_request()
>> - Check for nowait support with all the lower devices. Same with if adding a device which does not support nowait.
>> - Nowait under each raid is checked before the final I/O submission for the entire I/O.
>>
>> [1] https://patchwork.kernel.org/patch/9979887/
>
> Does this fix the partial IO issue we discussed before? It looks not to me. The
> partial IO bailed out could be any part of an IO, so simply returning the
> successed size doesn't help. Am I missing anything? I didn't follow the
> discussion, maybe Jens knew.
>
If the partial IO bailed out is any part of IO, isn't it supposed to
return the size of the IO succeeded _so far_? If a latter part of the IO
succeeds (with a failure in between) what are you supposed to return to
user in case of direct write()s? Would that even be correct in case it
is a file overwrite?
--
Goldwyn
next prev parent reply other threads:[~2017-10-06 12:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-04 13:55 [PATCH v2 0/9] Nowait support for stacked block devices Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 1/9] QUEUE_FLAG_NOWAIT to indicate device supports nowait Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 2/9] md: Add nowait support to md Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 3/9] md: raid1 nowait support Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 4/9] md: raid10 " Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 5/9] md: raid5 " Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 6/9] dm: add " Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 7/9] dm: Add nowait support to raid1 Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 8/9] dm: Add nowait support to dm-delay Goldwyn Rodrigues
2017-10-04 13:55 ` [PATCH 9/9] dm-mpath: Add nowait support Goldwyn Rodrigues
2017-10-05 17:19 ` [PATCH v2 0/9] Nowait support for stacked block devices Shaohua Li
2017-10-06 12:01 ` Goldwyn Rodrigues [this message]
2017-10-10 22:36 ` Shaohua Li
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=0bf484f7-1e95-86c4-c00d-125e22f73a8d@suse.de \
--to=rgoldwyn@suse.de \
--cc=axboe@kernel.dk \
--cc=linux-block@vger.kernel.org \
--cc=shli@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox