Re: [PATCH 1/4] ext4: Convert move_extent_per_page() to use folios

[Matthew Wilcox]

On Tue, Nov 15, 2022 at 06:10:08PM -0800, Vishal Moola (Oracle) wrote:
>  {
>  	struct inode *orig_inode = file_inode(o_filp);
>  	struct page *pagep[2] = {NULL, NULL};
> +	struct folio *folio[2] = {NULL, NULL};

I have a feeling that mext_page_double_lock() should also be converted
to use folios.  But this makes me nervous:

        int blocks_per_page = PAGE_SIZE >> orig_inode->i_blkbits;

and I'm not sure what will happen if one or both of the orig_page
and donor_page is large -- possibly different sizes of large.

Obviously ext4 doesn't allow large folios today, but it would be good to
get some reasoning about why this isn't laying a trap for later (or at
least assertions that neither folio is large so that there's an obvious
scream instead of silent data corruption).