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Subject: Re: [PATCH 05/15] mm: allow read-ahead with IOCB_NOWAIT set
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Dave Chinner <david@fromorbit.com>, io-uring@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, akpm@linux-foundation.org,
        Johannes Weiner <hannes@cmpxchg.org>
References: <20200618144355.17324-1-axboe@kernel.dk>
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 <20200624014645.GJ21350@casper.infradead.org>
 <bad52be9-ae44-171b-8dbf-0d98eedcadc0@kernel.dk>
 <70b0427c-7303-8f45-48bd-caa0562a2951@kernel.dk>
 <20200624164127.GP21350@casper.infradead.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <8835b6f2-b3c5-c9a0-2119-1fb161cf87dd@kernel.dk>
Date:   Wed, 24 Jun 2020 10:44:21 -0600
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On 6/24/20 10:41 AM, Matthew Wilcox wrote:
> On Wed, Jun 24, 2020 at 09:35:19AM -0600, Jens Axboe wrote:
>> On 6/24/20 9:00 AM, Jens Axboe wrote:
>>> On 6/23/20 7:46 PM, Matthew Wilcox wrote:
>>>> 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.
>>
>> We're already doing memalloc_nofs_save/restore in
>> page_cache_readahead_unbounded(), so I think all we need is to just do a
>> noio dance in generic_file_buffered_read() and that should be enough.
> 
> I think we can still sleep though, right?  I was thinking more
> like this:
> 
> http://git.infradead.org/users/willy/linux.git/shortlog/refs/heads/memalloc

Yeah, that's probably better. How do we want to handle this? I've already
got the other bits queued up. I can either add them to the series, or
pull a branch that'll go into Linus as well.

-- 
Jens Axboe