io-uring.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jens Axboe <axboe@kernel.dk>
To: io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org
Cc: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk
Subject: [PATCHSET v3 0/3] Add ability to save/restore iov_iter state
Date: Wed, 15 Sep 2021 10:29:34 -0600	[thread overview]
Message-ID: <20210915162937.777002-1-axboe@kernel.dk> (raw)

Hi,

Linus didn't particularly love the iov_iter->truncated addition and how
it was used, and it was hard to disagree with that. Instead of relying
on tracking ->truncated, add a few pieces of state so we can safely
handle partial or errored read/write attempts (that we want to retry).

Then we can get rid of the iov_iter addition, and at the same time
handle cases that weren't handled correctly before.

I've run this through vectored read/write with io_uring on the commonly
problematic cases (dm and low depth SCSI device) which trigger these
conditions often, and it seems to pass muster. I've also hacked in
faked randomly short reads and that helped find on issue with double
accounting. But it did validate the state handling otherwise.

For a discussion on this topic, see the thread here:

https://lore.kernel.org/linux-fsdevel/CAHk-=wiacKV4Gh-MYjteU0LwNBSGpWrK-Ov25HdqB1ewinrFPg@mail.gmail.com/

You can find these patches here:

https://git.kernel.dk/cgit/linux-block/log/?h=iov_iter.3

Changes since v2:
- Add comments on io_read() on the flow
- Fix issue with rw->bytes_done being incremented too early and hence
  double accounting if we enter that bottom do {} while loop in io_read()
- Restore iter at the bottom of do {} while loop in io_read()

Changes since v1:
- Drop 'did_bytes' from iov_iter_restore(). Only two cases in io_uring
  used it, and one of them had to be changed with v2. Better to just
  make the subsequent iov_iter_advance() explicit at that point.
- Cleanup and sanitize the io_uring side, and ensure it's sane around
  worker retries. No more digging into iov_iter_state from io_uring, we
  use it just for save/restore purposes.

-- 
Jens Axboe



             reply	other threads:[~2021-09-15 16:29 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-15 16:29 Jens Axboe [this message]
2021-09-15 16:29 ` [PATCH 1/3] iov_iter: add helper to save " Jens Axboe
2021-09-15 16:29 ` [PATCH 2/3] io_uring: use iov_iter state save/restore helpers Jens Axboe
2021-09-15 16:29 ` [PATCH 3/3] Revert "iov_iter: track truncated size" Jens Axboe
2021-09-15 18:32 ` [PATCHSET v3 0/3] Add ability to save/restore iov_iter state Linus Torvalds
2021-09-15 18:46   ` Jens Axboe
2021-09-15 19:26     ` Linus Torvalds
2021-09-15 19:40       ` Jens Axboe
2021-09-15 22:42         ` Jens Axboe
2021-09-16  1:15           ` Jens Axboe
2021-09-16  4:47 ` Al Viro
2021-09-16 16:10   ` Jens Axboe

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=20210915162937.777002-1-axboe@kernel.dk \
    --to=axboe@kernel.dk \
    --cc=io-uring@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=torvalds@linux-foundation.org \
    --cc=viro@zeniv.linux.org.uk \
    --subject='Re: [PATCHSET v3 0/3] Add ability to save/restore iov_iter state' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).