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Subject: Re: [PATCH 05/15] mm: allow read-ahead with IOCB_NOWAIT set
To:     =?UTF-8?Q?Andreas_Gr=c3=bcnbacher?= <andreas.gruenbacher@gmail.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
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        Linux-MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <b147aa47-940c-c641-3dac-8d99f8789a47@kernel.dk>
Date:   Tue, 7 Jul 2020 08:31:58 -0600
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On 7/7/20 5:38 AM, Andreas Grünbacher wrote:
> Am Mi., 24. Juni 2020 um 18:48 Uhr schrieb Jens Axboe <axboe@kernel.dk>:
>>
>> 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.
> 
> Also note my conflicting patch that introduces a IOCB_NOIO flag for
> fixing a gfs2 regression:
> 
> https://lore.kernel.org/linux-fsdevel/20200703095325.1491832-2-agruenba@redhat.com/

Yeah I noticed, pretty easy to resolve though.

-- 
Jens Axboe