Re: [PATCH] concurrent block allocation for ext3

[Andreas Dilger]

On Mar 10, 2003  18:41 +0300, Alex Tomas wrote:
> Here is the small patch which implements concurrent block allocation
> for ext3. It removes lock_super() in ext3_new_block() and ext3_free_blocks().
> Modifications of counters in superblock and group descriptors are protected
> by spinlock. Tested on SMP for several hours.

Any ideas on how much this improves the performance?  What sort of tests
were you running?  We could improve things a bit further by having separate
per-group locks for the update of the group descriptor info, and only
lazily update the superblock at statfs and unmount time (with a suitable
feature flag so e2fsck can fix this up at recovery time), but you seem
to have gotten the majority of the parallelism from this fix.

> @@ -214,11 +213,13 @@
>  				      block + i);
>  			BUFFER_TRACE(bitmap_bh, "bit already cleared");
>  		} else {
> +			spin_lock(&EXT3_SB(sb)->s_alloc_lock);
>  			dquot_freed_blocks++;
>  			gdp->bg_free_blocks_count =
>  			  cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count)+1);
>  			es->s_free_blocks_count =
>  			  cpu_to_le32(le32_to_cpu(es->s_free_blocks_count)+1);
> +			spin_unlock(&EXT3_SB(sb)->s_alloc_lock);

One minor nit is that you left an ext3_error() for the "bit already cleared"
case just above this patch hunk.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/