Re: [PATCH 04/18] fs: Implement lazy LRU updates for inodes.

Christoph Hellwig
2010-10-08T07:08:59Z

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

A few nipicks on the comments or lack thereof below:

> @@ -489,8 +484,15 @@ static void prune_icache(int nr_to_scan)
>
> inode = list_entry(inode_unused.prev, struct inode, i_list);
>
> - if (inode->i_state || atomic_read(&inode->i_count)) {
> + if (atomic_read(&inode->i_count) ||
> + (inode->i_state & ~I_REFERENCED)) {
> + list_del_init(&inode->i_list);
> + percpu_counter_dec(&nr_inodes_unused);
> + continue;
> + }
> + if (inode->i_state & I_REFERENCED) {
> list_move(&inode->i_list, &inode_unused);
> + inode->i_state &= ~I_REFERENCED;
> continue;

I think this code could use some comments explaining the lazy LRU
scheme.

> - if (inode != list_entry(inode_unused.next,
> - struct inode, i_list))
> - continue; /* wrong inode or list_empty */
> - if (!can_unuse(inode))
> + /*
> + * if we can't reclaim this inod immediately, give it
> + * another pass through the free list so we don't spin
> + * on it.

s/inod/inode/

> +
> + /*
> + * We avoid moving dirty inodes back onto the LRU now because I_FREEING
> + * is set and hence writeback_single_inode() won't move the inode
> + * around.
> + */
> + if (!list_empty(&inode->i_list)) {
> + list_del_init(&inode->i_list);
> + percpu_counter_dec(&nr_inodes_unused);
> + }
> +

The comment is a bit misleading. We do not only avoid moving it to the
LRU, but actively delete the inode from the LRU here. I don't think the
I_FREEING check isn't the only reason - the LRU code traditionally
couldn't deal with unlinked inodes at all, although the switch to
->evict_inode probably has fixed that.