linux-ext4 - Re: mke2fs with bigalloc is too slow

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Message-ID: <20130315142844.GA7403@thunk.org>
Date:	Fri, 15 Mar 2013 10:28:44 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Andrey Sidorov <qrxd43@...orola.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: mke2fs with bigalloc is too slow

On Fri, Mar 15, 2013 at 01:53:58AM +0400, Andrey Sidorov wrote:
>
> Oh, thanks for pointing that! I was mostly reading v1.42 that is more
> than year old and missed the fact 1.42.7 has rbtree bitmap
> implementation.
> That explains why formatting bigalloc became slower compared to 1.42.
> In this case ffs/ffz seem like a right choice, I'll try them. I'll
> also try mirroring as it won't waste much RAM and might be faster.

As you'll discover fairly quickly, we haven't implemented ffs/ffz for
rbtree bitmaps yet.  We've implemented find_first_zero for for
bitarrays (and for the generic bitmap framework in lib/ext2fs/bitops.h
and lib/ext2fs/gen_bitmap*.c), but not in lib/ext2fs/blkmap64_rb.c
yet.  More critically for the mke2fs's use case in
convert_subcluster_bitmap, will be the find_first_set operation.

Adding this has been on my todo list for a while, but I just haven't
had the time.  Note that test cases for this will be critically
important, especially if we start using them in correctness-critical
code such as e2fsck.

                                                - Ted

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