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

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Message-ID: <20200624164127.GP21350@casper.infradead.org>
Date:   Wed, 24 Jun 2020 17:41:27 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Dave Chinner <david@...morbit.com>, 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 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