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From: Trond Myklebust <trondmy@hammerspace.com>
To: "axboe@kernel.dk" <axboe@kernel.dk>,
	"io-uring@vger.kernel.org" <io-uring@vger.kernel.org>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 05/12] mm: support async buffered reads in generic_file_buffered_read()
Date: Sun, 24 May 2020 14:05:31 +0000
Message-ID: <264614fc4fa08df2b0899da1cd38bb07150cd7f3.camel@hammerspace.com> (raw)
In-Reply-To: <20200523185755.8494-6-axboe@kernel.dk>

On Sat, 2020-05-23 at 12:57 -0600, Jens Axboe wrote:
> Use the async page locking infrastructure, if IOCB_WAITQ is set in
> the
> passed in iocb. The caller must expect an -EIOCBQUEUED return value,
> which means that IO is started but not done yet. This is similar to
> how
> O_DIRECT signals the same operation. Once the callback is received by
> the caller for IO completion, the caller must retry the operation.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  mm/filemap.c | 33 ++++++++++++++++++++++++++-------
>  1 file changed, 26 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index c746541b1d49..a3b86c9acdc8 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1219,6 +1219,14 @@ static int __wait_on_page_locked_async(struct
> page *page,
>  	return ret;
>  }
>  
> +static int wait_on_page_locked_async(struct page *page,
> +				     struct wait_page_queue *wait)
> +{
> +	if (!PageLocked(page))
> +		return 0;
> +	return __wait_on_page_locked_async(compound_head(page), wait,
> false);
> +}
> +
>  /**
>   * put_and_wait_on_page_locked - Drop a reference and wait for it to
> be unlocked
>   * @page: The page to wait for.
> @@ -2058,17 +2066,25 @@ static ssize_t
> generic_file_buffered_read(struct kiocb *iocb,
>  					index, last_index - index);
>  		}
>  		if (!PageUptodate(page)) {
> -			if (iocb->ki_flags & IOCB_NOWAIT) {
> -				put_page(page);
> -				goto would_block;
> -			}
> -
>  			/*
>  			 * See comment in do_read_cache_page on why
>  			 * wait_on_page_locked is used to avoid
> unnecessarily
>  			 * serialisations and why it's safe.
>  			 */
> -			error = wait_on_page_locked_killable(page);
> +			if (iocb->ki_flags & IOCB_WAITQ) {
> +				if (written) {
> +					put_page(page);
> +					goto out;
> +				}
> +				error = wait_on_page_locked_async(page,
> +								iocb-
> >private);

If it is being used in 'generic_file_buffered_read()' as storage for a
wait queue, then it is hard to consider this a 'private' field.

Perhaps either rename and add type checking, or else add a separate
field altogether to struct kiocb?

> +			} else {
> +				if (iocb->ki_flags & IOCB_NOWAIT) {
> +					put_page(page);
> +					goto would_block;
> +				}
> +				error =
> wait_on_page_locked_killable(page);
> +			}
>  			if (unlikely(error))
>  				goto readpage_error;
>  			if (PageUptodate(page))
> @@ -2156,7 +2172,10 @@ static ssize_t
> generic_file_buffered_read(struct kiocb *iocb,
>  
>  page_not_up_to_date:
>  		/* Get exclusive access to the page ... */
> -		error = lock_page_killable(page);
> +		if (iocb->ki_flags & IOCB_WAITQ)
> +			error = lock_page_async(page, iocb->private);
> +		else
> +			error = lock_page_killable(page);
>  		if (unlikely(error))
>  			goto readpage_error;
>  
-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com



  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-23 18:57 [PATCHSET v2 0/12] Add support for async buffered reads Jens Axboe
2020-05-23 18:57 ` [PATCH 01/12] block: read-ahead submission should imply no-wait as well Jens Axboe
2020-05-23 18:57 ` [PATCH 02/12] mm: allow read-ahead with IOCB_NOWAIT set Jens Axboe
2020-05-23 18:57 ` [PATCH 03/12] mm: abstract out wake_page_match() from wake_page_function() Jens Axboe
2020-05-23 18:57 ` [PATCH 04/12] mm: add support for async page locking Jens Axboe
2020-05-23 18:57 ` [PATCH 05/12] mm: support async buffered reads in generic_file_buffered_read() Jens Axboe
2020-05-24 14:05   ` Trond Myklebust [this message]
2020-05-24 16:30     ` Jens Axboe
2020-05-24 16:40       ` Jens Axboe
2020-05-24 17:11         ` Trond Myklebust
2020-05-24 17:12           ` Jens Axboe
2020-05-23 18:57 ` [PATCH 06/12] fs: add FMODE_BUF_RASYNC Jens Axboe
2020-05-23 18:57 ` [PATCH 07/12] ext4: flag as supporting buffered async reads Jens Axboe
2020-05-23 18:57 ` [PATCH 08/12] block: flag block devices as supporting IOCB_WAITQ Jens Axboe
2020-05-23 18:57 ` [PATCH 09/12] xfs: flag files as supporting buffered async reads Jens Axboe
2020-05-23 18:57 ` [PATCH 10/12] btrfs: " Jens Axboe
2020-05-23 18:57 ` [PATCH 11/12] mm: add kiocb_wait_page_queue_init() helper Jens Axboe
2020-05-23 18:57 ` [PATCH 12/12] io_uring: support true async buffered reads, if file provides it Jens Axboe
2020-05-25  7:29   ` Pavel Begunkov
2020-05-25 19:59     ` Jens Axboe
2020-05-26  7:44       ` Pavel Begunkov
2020-05-26 13:50         ` Jens Axboe
2020-05-26  7:38   ` Pavel Begunkov
2020-05-26 13:47     ` Jens Axboe
2020-05-23 19:20 ` [PATCHSET v2 0/12] Add support for async buffered reads Jens Axboe
2020-05-24  9:46   ` Chris Panayis
2020-05-24 19:24     ` Jens Axboe
2020-05-24 19:21 [PATCHSET v4 " Jens Axboe
2020-05-24 19:21 ` [PATCH 05/12] mm: support async buffered reads in generic_file_buffered_read() Jens Axboe
2020-05-26 19:51 [PATCHSET v5 0/12] Add support for async buffered reads Jens Axboe
2020-05-26 19:51 ` [PATCH 05/12] mm: support async buffered reads in generic_file_buffered_read() Jens Axboe
2020-05-26 22:00   ` Johannes Weiner

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