linux-kernel - Re: [PATCH 05/15] mm: allow read-ahead with IOCB

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Message-ID: <20200810225601.GE2079@dread.disaster.area>
Date:   Tue, 11 Aug 2020 08:56:01 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Matthew Wilcox <willy@...radead.org>, io-uring@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 05/15] mm: allow read-ahead with IOCB_NOWAIT set

On Wed, Jun 24, 2020 at 10:44:21AM -0600, Jens Axboe wrote:
> 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, Willy,

Now that this patch has been merged and IOCB_NOWAIT semantics ifor
buffered reads are broken in Linus' tree, what's the plan to get
this regression fixed before 5.9 releases?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com