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From: Jens Axboe <[email protected]>
To: Matthew Wilcox <[email protected]>, Dave Chinner <[email protected]>
Cc: [email protected], [email protected],
	[email protected], [email protected],
	[email protected], Johannes Weiner <[email protected]>
Subject: Re: [PATCH 05/15] mm: allow read-ahead with IOCB_NOWAIT set
Date: Wed, 24 Jun 2020 09:00:46 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 6/23/20 7:46 PM, Matthew Wilcox wrote:
> On Wed, Jun 24, 2020 at 11:02:53AM +1000, Dave Chinner wrote:
>> On Thu, Jun 18, 2020 at 08:43:45AM -0600, Jens Axboe wrote:
>>> The read-ahead shouldn't block, so allow it to be done even if
>>> IOCB_NOWAIT is set in the kiocb.
>>
>> Doesn't think break preadv2(RWF_NOWAIT) semantics for on buffered
>> reads? i.e. this can now block on memory allocation for the page
>> cache, which is something RWF_NOWAIT IO should not do....
> 
> Yes.  This eventually ends up in page_cache_readahead_unbounded()
> which gets its gfp flags from readahead_gfp_mask(mapping).
> 
> I'd be quite happy to add a gfp_t to struct readahead_control.
> The other thing I've been looking into for other reasons is adding
> a memalloc_nowait_{save,restore}, which would avoid passing down
> the gfp_t.

That was my first thought, having the memalloc_foo_save/restore for
this. I don't think adding a gfp_t to readahead_control is going
to be super useful, seems like the kind of thing that should be
non-blocking by default.

-- 
Jens Axboe


  reply	other threads:[~2020-06-24 15:00 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
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 [this message]
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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