linux-ext4 - Re: e2fsck: set dir_nlink feature if large dir exists

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Date:   Wed, 30 Aug 2017 11:13:32 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: e2fsck: set dir_nlink feature if large dir exists

On Wed, Aug 30, 2017 at 01:43:30AM -0600, Andreas Dilger wrote:
> > The f_large_dir test is now failing after I apply this patch:
> > 
> > debugfs 1.43.6 (29-Aug-2017)
> > ./test_one: 38: /usr/projects/e2fsprogs/e2fsprogs/tests/f_large_dir/script: arithmetic expression: division by zero: "i / ELAPSED"
> > f_large_dir: optimize 3 level htree directories: failed
> 
> You must have a faster test system than I do...

I'm using a ramdisk for /tmp.  I suspect that's what is making all the
difference.  Otherwise it's just a normal Lenovo T470 laptop....

> On a related note, I was trying to implement the optimization for
> more efficient ext2fs_link() insertion, but this has proven to be
> much more complex than I expected.  I was thinking I would just
> call the link_proc() function directly to handle insertion of the
> new name, using block number of the previous caller.  However, this
> function depends on the directory leaf buffers having been read
> from disk, and being passed a dirent pointer to the free space after
> being called through a series of callback indirections.

I think it's more trouble than it's worth to preseve the existing
link_proc() function.  I'd recommend out to be just what is necessary
to do the directory entry insert, and make that a helper function
which is called by link_proc() and the shortcut handling code in
ext2fs_link().

Cheers,

						- Ted