linux-ext4 - Re: [PATCH 2/2] ext4: flush delalloc blocks when space is low

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20091216204602.GC28425@atrey.karlin.mff.cuni.cz>
Date:	Wed, 16 Dec 2009 21:46:02 +0100
From:	Jan Kara <jack@...e.cz>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 2/2] ext4: flush delalloc blocks when space is low

> Creating many small files in rapid succession on a small
> filesystem can lead to spurious ENOSPC; on a 104MB filesystem:
> 
> for i in `seq 1 22500`; do
>     echo -n > $SCRATCH_MNT/$i
>     echo XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX > $SCRATCH_MNT/$i
> done
> 
> leads to ENOSPC even though after a sync, 40% of the fs is free
> again.
> 
> This is because we reserve worst-case metadata for delalloc writes,
> and when data is allocated that worst-case reservation is not
> usually needed.
> 
> When freespace is low, kicking off an async writeback will start
> converting that worst-case space usage into something more realistic,
> almost always freeing up space to continue.
> 
> This resolves the testcase for me, and survives all 4 generic
> ENOSPC tests in xfstests.
> 
> We'll still need a hard synchronous sync to squeeze out the last bit,
> but this fixes things up to a large degree.
> 
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
  Looks good.

  Acked-by: Jan Kara <jack@...e.cz>

							Honza
> ---
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 5c5bc5d..5b3f468 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3024,11 +3024,18 @@ static int ext4_nonda_switch(struct super_block *sb)
>  	if (2 * free_blocks < 3 * dirty_blocks ||
>  		free_blocks < (dirty_blocks + EXT4_FREEBLOCKS_WATERMARK)) {
>  		/*
> -		 * free block count is less that 150% of dirty blocks
> -		 * or free blocks is less that watermark
> +		 * free block count is less than 150% of dirty blocks
> +		 * or free blocks is less than watermark
>  		 */
>  		return 1;
>  	}
> +	/*
> +	 * Even if we don't switch but are nearing capacity,
> +	 * start pushing delalloc when 1/2 of free blocks are dirty.
> +	 */
> +	if (free_blocks < 2 * dirty_blocks)
> +		writeback_inodes_sb_if_idle(sb);
> +
>  	return 0;
>  }
>  
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html