linux-ext4 - Re: [PATCH] libext2fs: readahead for meta

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Date:   Tue, 28 Feb 2017 08:16:02 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Artem Blagodarenko <artem.blagodarenko@...il.com>
Cc:     linux-ext4@...r.kernel.org, adilger.kernel@...ger.ca,
        alexey.lyashkov@...il.com
Subject: Re: [PATCH] libext2fs: readahead for meta_bg

On Mon, Feb 20, 2017 at 01:03:45PM +0300, Artem Blagodarenko wrote:
> From: Alexey Lyashkov <alexey.lyashkov@...gate.com>
> 
> There are ~37k of random IOs with meta_bg option on 300T target.

Yikes, 300TB ext4! :)

(Is that really 2.2 million blockgroups?)

> Debugfs requires 20 minutes to be started. Enabling readahead for
> group blocks metadata save time dramatically. Only 12s to start.
> 
> Signed-off-by: Alexey Lyashkov <alexey.lyashkov@...gate.com>

Looks good,
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>

--D

> ---
>  lib/ext2fs/openfs.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
> index ba501e6..f158b0a 100644
> --- a/lib/ext2fs/openfs.c
> +++ b/lib/ext2fs/openfs.c
> @@ -399,6 +399,12 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
>  #endif
>  		dest += fs->blocksize*first_meta_bg;
>  	}
> +
> +	for (i = first_meta_bg ; i < fs->desc_blocks; i++) {
> +		blk = ext2fs_descriptor_block_loc2(fs, group_block, i);
> +		io_channel_cache_readahead(fs->io, blk, 1);
> +	}
> +
>  	for (i=first_meta_bg ; i < fs->desc_blocks; i++) {
>  		blk = ext2fs_descriptor_block_loc2(fs, group_block, i);
>  		retval = io_channel_read_blk64(fs->io, blk, 1, dest);
> -- 
> 1.7.1
>