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

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Date:	Sun, 10 Aug 2014 23:31:20 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 5/6] libext2fs/e2fsck: provide routines to read-ahead
 metadata

On Mon, Aug 11, 2014 at 02:24:15AM -0400, Theodore Ts'o wrote:
> 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.

Hmm, I'll try that, though I'm almost tempted just to issue io_cache_readahead
calls directly from the for loop.  The only reason I'm using the list here at
all is to handle the case of reading multiple groups in a flexbg (pass5 RA).

--D
> 
> 						- Ted
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