On Tue, 14 Nov 2017 16:56:47 -0500 Josef Bacik <jo...@toxicpanda.com> wrote:

> From: Josef Bacik <jba...@fb.com>
> 
> The only reason we pass in the mapping is to get the inode in order to see if
> writeback cgroups is enabled, and even then it only checks the bdi and a super
> block flag.  balance_dirty_pages() doesn't even use the mapping.  Since
> balance_dirty_pages*() works on a bdi level, just pass in the bdi and super
> block directly so we can avoid using mapping.  This will allow us to still use
> balance_dirty_pages for dirty metadata pages that are not backed by an
> address_mapping.
>
> ...
> 
> @@ -71,7 +72,8 @@ static int _block2mtd_erase(struct block2mtd_dev *dev, 
> loff_t to, size_t len)
>                               memset(page_address(page), 0xff, PAGE_SIZE);
>                               set_page_dirty(page);
>                               unlock_page(page);
> -                             balance_dirty_pages_ratelimited(mapping);
> +                             
> balance_dirty_pages_ratelimited(inode_to_bdi(inode),
> +                                                             inode->i_sb);
>                               break;
>                       }

So we do a bunch more work in each caller and we pass two args rather
than one.  That doesn't make things better!

I see that this is enablement for "dirty metadata pages that are not
backed by an address_mapping" (address_space) so I look into [7/10] and
the changelog doesn't tell me much.

So color me confused.  What is this patchset actually *for*?  Is there
some filesystem which has non-address_space-backed metadata?  Or will
there be so soon?  Or what.

I think we need a [0/n] email please.  One which fully describes the
intent of the patchset.

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