linux-ext4 - Re: [RFC] fadvise: add more flags to provide a hint for block allocation

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Message-ID: <20120307005130.GH3592@dastard>
Date:	Wed, 7 Mar 2012 11:51:30 +1100
From:	Dave Chinner <david@...morbit.com>
To:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [RFC] fadvise: add more flags to provide a hint for block
 allocation

On Mon, Mar 05, 2012 at 08:50:29PM +0800, Zheng Liu wrote:
> Hi list,
> 
> Block allocation is a key component of file system.  Every file systems try to
> improve the performance with optimizing the block allocation of a file.  But no
> matter what file system does, it just guesses what the user expects.  Thus, it
> is not very accurate.  fadvise(2) provides a method to let the user to give a
> hint to file system.  However, until now, only few flags are provided.  So we
> can provide more flags to tell file system how to allocate the blocks for a
> file.
> 
> For example:
> we can add these flags into fadvise(2):
> FADV_ALLOC_READ_SEQ

fallocate()

> FADV_ALLOC_READ_RANDOM

Allocation can't be optimised as the read pattern cannot be defined.

> FADV_ALLOC_WRITE_ONCE

fallocate()

> FADV_ALLOC_WRITE_APPEND

chattr +a

Cheers,

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