linux-kernel - Re: bcache on XFS: metadata I/O (dirent I/O?) not getting cached at all?

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Date:   Thu, 7 Feb 2019 01:24:25 +0100
From:   Andre Noll <maan@...bingen.mpg.de>
To:     Dave Chinner <david@...morbit.com>
Cc:     Nix <nix@...eri.org.uk>, linux-bcache@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Coly Li <colyli@...e.de>
Subject: Re: bcache on XFS: metadata I/O (dirent I/O?) not getting cached at
 all?

On Thu, Feb 07, 10:43, Dave Chinner wrote
> File data readahead: REQ_RAHEAD
> Metadata readahead: REQ_META | REQ_RAHEAD
> 
> drivers/md/bcache/request.c::check_should_bypass():
> 
>         /*
>          * Flag for bypass if the IO is for read-ahead or background,
>          * unless the read-ahead request is for metadata (eg, for gfs2).
>          */
>         if (bio->bi_opf & (REQ_RAHEAD|REQ_BACKGROUND) &&
>             !(bio->bi_opf & REQ_PRIO))
>                 goto skip;
> 
> bcache needs fixing - it thinks REQ_PRIO means metadata IO. That's
> wrong - REQ_META means it's metadata IO, and so this is a bcache
> bug.

Do you think 752f66a75abad is bad (ha!) and should be reverted?

Thanks
Andre
-- 
Max Planck Institute for Developmental Biology
Max-Planck-Ring 5, 72076 Tübingen, Germany. Phone: (+49) 7071 601 829
http://people.tuebingen.mpg.de/maan/

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