linux-ext4 - Re: [PATCH 5/6] libext2fs/e2fsck: provide routines to read-ahead metadata

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Date:	Mon, 11 Aug 2014 02:24:15 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 5/6] libext2fs/e2fsck: provide routines to read-ahead
 metadata

On Sun, Aug 10, 2014 at 10:21:51PM -0700, Darrick J. Wong wrote:
> 
> It turns out that each of the calls to ext2fs_resize_mem in the
> ext2fs_add_dir_block2() function is costing us ~2ms for each call to this
> function.  I'll add a new ext2fs_init_dblist() APi that lets us specify the
> initial size of the list.  This seems to reduce the fsck runtime by a few more
> seconds.

I suspect dblist is the wrong abstraction to use here.  Since the
blocks we want to read ahead are generally going to be contiguous, why
not use a rbtree bitmap, setting the blocks that should be subject to
readahead, and then use the find_first_set() function to iterate over
the bitmap?  Or if you want to be even more efficient, create an
interator function which takes a bitmap and returns blocks that are
set in the bitmap, one by one.

						- Ted
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