linux-ext4 - Re: [PATCH] fs-verity: implement readahead of Merkle tree pages

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Message-ID: <20200106204357.GA254289@gmail.com>
Date:   Mon, 6 Jan 2020 12:43:58 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, Victor Hsieh <victorhsieh@...gle.com>,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] fs-verity: implement readahead of Merkle tree pages

On Mon, Jan 06, 2020 at 10:15:08AM -0800, Jaegeuk Kim wrote:
> >  static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
> > -					       pgoff_t index)
> > +					       pgoff_t index,
> > +					       unsigned long num_ra_pages)
> >  {
> > +	struct page *page;
> > +
> >  	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
> >  
> > -	return read_mapping_page(inode->i_mapping, index, NULL);
> > +	page = find_get_page(inode->i_mapping, index);
> > +	if (!page || !PageUptodate(page)) {
> > +		if (page)
> > +			put_page(page);
> > +		else if (num_ra_pages > 1)
> > +			f2fs_merkle_tree_readahead(inode->i_mapping, index,
> > +						   num_ra_pages);
> > +		page = read_mapping_page(inode->i_mapping, index, NULL);
> > +		if (IS_ERR(page))
> > +			return page;
> 
> We don't need to check this, but can use the below return page?
> 

Indeed, I'll remove the unnecessary IS_ERR(page) check.

> > +	}
> 
> mark_page_accessed(page)?
> 
> > +	return page;
> >  }

Good idea, but read_mapping_page() already calls mark_page_accessed().  It's
just find_get_page() that doesn't.  So after this patch, mark_page_accessed() is
no longer called in the case where the page is already cached and Uptodate.
I'll change it to use:

	find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);

- Eric