linux-ext4 - Re: [PATCH 23/25] ext2fs: add readahead method to improve scanning

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Message-ID: <20140911211031.GA17990@thunk.org>
Date:	Thu, 11 Sep 2014 17:10:31 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org,
	Andreas Dilger <andreas.dilger@...el.com>
Subject: Re: [PATCH 23/25] ext2fs: add readahead method to improve scanning

On Mon, Sep 08, 2014 at 04:14:08PM -0700, Darrick J. Wong wrote:
> Frøm: Andreas Dilger <adilger@...mcloud.com>
> 
> Add a readahead method for prefetching ranges of disk blocks.  This is
> useful for inode table scanning, and other large contiguous ranges of
> blocks, and may also prove useful for random block prefetch, since it
> will allow reordering of the IO without waiting synchronously for the
> reads to complete.
> 
> It is currently using the posix_fadvise(POSIX_FADV_WILLNEED)
> interface, as this proved most efficient during our testing.
> 
> [darrick.wong@...cle.com]
> Make the arguments to the readahead function take the same ULL values
> as the other IO functions, and return an appropriate error code when
> fadvise isn't available.
> 
> Signed-off-by: Andreas Dilger <andreas.dilger@...el.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
>  lib/ext2fs/ext2_io.h    |    8 +++++++-
>  lib/ext2fs/io_manager.c |    9 +++++++++
>  lib/ext2fs/unix_io.c    |   27 ++++++++++++++++++++++++---
>  3 files changed, 40 insertions(+), 4 deletions(-)

Could you also plumb through the new method in test_io.c?  Because we
often use this to interposed between mke2fs or e2fsprogs and unix_io.c
for debugging purposes.

Thanks!

						- Ted
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