linux-ext4 - Re: [PATCH 1/4] ext4: Convert move_extent_per

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Date:   Wed, 16 Nov 2022 08:09:22 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
        akpm@...ux-foundation.org, naoya.horiguchi@....com, tytso@....edu
Subject: Re: [PATCH 1/4] ext4: Convert move_extent_per_page() to use folios

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).