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Subject: Re: [PATCHSET v5 0/12] Add support for async buffered reads
To:     Andres Freund <andres@anarazel.de>
Cc:     io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <0179d0bf-0b01-3f05-9221-654a00f0452d@kernel.dk>
Date:   Fri, 5 Jun 2020 16:56:44 -0600
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On 6/5/20 4:54 PM, Andres Freund wrote:
> Hi,
> 
> On 2020-06-05 16:49:24 -0600, Jens Axboe wrote:
>> Yes that's expected, if we have to fallback to ->readpage(), then it'll
>> go to a worker. read-ahead is what drives the async nature of it, as we
>> issue the range (plus more, depending on RA window) as read-ahead for
>> the normal read, then wait for it.
> 
> But I assume async would still work for files with POSIX_FADV_RANDOM
> set, or not? Assuming the system wide setting isn't zero, of course.

Yes it'll work if FADV_RANDOM is set. But just not if read-ahead is
totally disabled. I guess we could make that work too, though not sure
that it's super important.

-- 
Jens Axboe