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From: Jens Axboe <[email protected]>
To: Pavel Begunkov <[email protected]>, [email protected]
Cc: [email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [PATCH 04/15] io_uring: re-issue block requests that failed because of resources
Date: Fri, 19 Jun 2020 08:22:22 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 6/19/20 8:12 AM, Pavel Begunkov wrote:
> On 18/06/2020 17:43, Jens Axboe wrote:
>> Mark the plug with nowait == true, which will cause requests to avoid
>> blocking on request allocation. If they do, we catch them and reissue
>> them from a task_work based handler.
>>
>> Normally we can catch -EAGAIN directly, but the hard case is for split
>> requests. As an example, the application issues a 512KB request. The
>> block core will split this into 128KB if that's the max size for the
>> device. The first request issues just fine, but we run into -EAGAIN for
>> some latter splits for the same request. As the bio is split, we don't
>> get to see the -EAGAIN until one of the actual reads complete, and hence
>> we cannot handle it inline as part of submission.
>>
>> This does potentially cause re-reads of parts of the range, as the whole
>> request is reissued. There's currently no better way to handle this.
>>
>> Signed-off-by: Jens Axboe <[email protected]>
>> ---
>>  fs/io_uring.c | 148 ++++++++++++++++++++++++++++++++++++++++++--------
>>  1 file changed, 124 insertions(+), 24 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 2e257c5a1866..40413fb9d07b 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -900,6 +900,13 @@ static int io_file_get(struct io_submit_state *state, struct io_kiocb *req,
>>  static void __io_queue_sqe(struct io_kiocb *req,
>>  			   const struct io_uring_sqe *sqe);
>>  
> ...> +
>> +static void io_rw_resubmit(struct callback_head *cb)
>> +{
>> +	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
>> +	struct io_ring_ctx *ctx = req->ctx;
>> +	int err;
>> +
>> +	__set_current_state(TASK_RUNNING);
>> +
>> +	err = io_sq_thread_acquire_mm(ctx, req);
>> +
>> +	if (io_resubmit_prep(req, err)) {
>> +		refcount_inc(&req->refs);
>> +		io_queue_async_work(req);
>> +	}
> 
> Hmm, I have similar stuff but for iopoll. On top removing grab_env* for
> linked reqs and some extra. I think I'll rebase on top of this.

Yes, there's certainly overlap there. I consider this series basically
wrapped up, so feel free to just base on top of it.

>> +static bool io_rw_reissue(struct io_kiocb *req, long res)
>> +{
>> +#ifdef CONFIG_BLOCK
>> +	struct task_struct *tsk;
>> +	int ret;
>> +
>> +	if ((res != -EAGAIN && res != -EOPNOTSUPP) || io_wq_current_is_worker())
>> +		return false;
>> +
>> +	tsk = req->task;
>> +	init_task_work(&req->task_work, io_rw_resubmit);
>> +	ret = task_work_add(tsk, &req->task_work, true);
> 
> I don't like that the request becomes un-discoverable for cancellation
> awhile sitting in the task_work list. Poll stuff at least have hash_node
> for that.

Async buffered IO was never cancelable, so it doesn't really matter.
It's tied to the task, so we know it'll get executed - either run, or
canceled if the task is going away. This is really not that different
from having the work discoverable through io-wq queueing before, since
the latter could never be canceled anyway as it sits there
uninterruptibly waiting for IO completion.

-- 
Jens Axboe


  reply	other threads:[~2020-06-19 14:22 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-18 14:43 Jens Axboe
2020-06-18 14:43 ` [PATCH 01/15] block: provide plug based way of signaling forced no-wait semantics Jens Axboe
2020-06-18 14:43 ` [PATCH 02/15] io_uring: always plug for any number of IOs Jens Axboe
2020-06-18 14:43 ` [PATCH 03/15] io_uring: catch -EIO from buffered issue request failure Jens Axboe
2020-06-18 14:43 ` [PATCH 04/15] io_uring: re-issue block requests that failed because of resources Jens Axboe
2020-06-19 14:12   ` Pavel Begunkov
2020-06-19 14:22     ` Jens Axboe [this message]
2020-06-19 14:30       ` Pavel Begunkov
2020-06-19 14:36         ` Jens Axboe
2020-06-18 14:43 ` [PATCH 05/15] mm: allow read-ahead with IOCB_NOWAIT set Jens Axboe
2020-06-24  1:02   ` Dave Chinner
2020-06-24  1:46     ` Matthew Wilcox
2020-06-24 15:00       ` Jens Axboe
2020-06-24 15:35         ` Jens Axboe
2020-06-24 16:41           ` Matthew Wilcox
2020-06-24 16:44             ` Jens Axboe
2020-07-07 11:38               ` Andreas Grünbacher
2020-07-07 14:31                 ` Jens Axboe
2020-08-10 22:56               ` Dave Chinner
2020-08-10 23:03                 ` Jens Axboe
2020-06-24  4:38   ` Dave Chinner
2020-06-24 15:01     ` Jens Axboe
2020-06-18 14:43 ` [PATCH 06/15] mm: abstract out wake_page_match() from wake_page_function() Jens Axboe
2020-06-18 14:43 ` [PATCH 07/15] mm: add support for async page locking Jens Axboe
2020-07-07 11:32   ` Andreas Grünbacher
2020-07-07 14:32     ` Jens Axboe
2020-06-18 14:43 ` [PATCH 08/15] mm: support async buffered reads in generic_file_buffered_read() Jens Axboe
2020-06-18 14:43 ` [PATCH 09/15] fs: add FMODE_BUF_RASYNC Jens Axboe
2020-06-18 14:43 ` [PATCH 10/15] block: flag block devices as supporting IOCB_WAITQ Jens Axboe
2020-06-18 14:43 ` [PATCH 11/15] xfs: flag files as supporting buffered async reads Jens Axboe
2020-06-18 14:43 ` [PATCH 12/15] btrfs: " Jens Axboe
2020-06-19 11:11   ` David Sterba
2020-06-18 14:43 ` [PATCH 13/15] ext4: flag " Jens Axboe
2020-06-18 14:43 ` [PATCH 14/15] mm: add kiocb_wait_page_queue_init() helper Jens Axboe
2020-06-18 14:43 ` [PATCH 15/15] io_uring: support true async buffered reads, if file provides it Jens Axboe
2020-06-23 12:39   ` Pavel Begunkov
2020-06-23 14:38     ` Jens Axboe
2020-06-18 14:45 ` [PATCHSET v7 0/12] Add support for async buffered reads Jens Axboe

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