linux-ext4 - Re: A bug in ext4 with big directories (was: NVFS XFS metadata)

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Date:   Wed, 23 Sep 2020 11:44:57 +0200
From:   Jan Kara <jack@...e.cz>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Eric Sandeen <esandeen@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: A bug in ext4 with big directories (was: NVFS XFS metadata)

Hi!

On Wed 23-09-20 05:20:55, Mikulas Patocka wrote:
> There seems to be a bug in ext4 - when I create very large directory, ext4 
> fails with -ENOSPC despite the fact that there is plenty of free space and 
> free inodes on the filesystem.
> 
> How to reproduce:
> download the program dir-test: 
> http://people.redhat.com/~mpatocka/benchmarks/dir-test.c
> 
> # modprobe brd rd_size=67108864
> # mkfs.ext4 /dev/ram0
> # mount -t ext4 /dev/ram0 /mnt/test
> # dir-test /mnt/test/ 8000000 8000000
> deleting: 7999000
> 2540000
> file 2515327 can't be created: No space left on device
> # df /mnt/test
> /dev/ram0        65531436 633752 61525860   2% /mnt/test
> # df -i /mnt/test
> /dev/ram0        4194304 1881547 2312757   45% /mnt/test

Yeah, you likely run out of space in ext4 directory h-tree. You can enable
higher depth h-trees with large_dir feature (mkfs.ext4 -O large_dir). Does
that help?

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR