linux-kernel - Re: [PATCH 2/2] mm/hugetlb: add wrapper functions for interactions with page cache

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Message-ID: <ZIOHL1dtyoaR1S/w@casper.infradead.org>
Date:   Fri, 9 Jun 2023 21:10:23 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, songmuchun@...edance.com,
        mike.kravetz@...cle.com, david@...hat.com, nphamcs@...il.com,
        jthoughton@...gle.com
Subject: Re: [PATCH 2/2] mm/hugetlb: add wrapper functions for interactions
 with page cache

On Fri, Jun 09, 2023 at 12:49:47PM -0700, Sidhartha Kumar wrote:
> +++ b/fs/hugetlbfs/inode.c
> @@ -617,20 +617,19 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
>  	struct hstate *h = hstate_inode(inode);
>  	struct address_space *mapping = &inode->i_data;
>  	const pgoff_t start = lstart >> huge_page_shift(h);
> -	const pgoff_t end = lend >> huge_page_shift(h);
>  	struct folio_batch fbatch;
>  	pgoff_t next, index;
>  	int i, freed = 0;
>  	bool truncate_op = (lend == LLONG_MAX);
>  
>  	folio_batch_init(&fbatch);
> -	next = start;
> -	while (filemap_get_folios(mapping, &next, end - 1, &fbatch)) {
> +	next = lstart;

That's suspicious.  Surely it should be

	next = lstart / PAGE_SIZE;

> +	while (filemap_get_folios(mapping, &next, lend - 1, &fbatch)) {

and 'end' is supposed to be a pgoff_t, so lend - 1 is also suspicious.

> -			index = folio->index;
> +			index = (folio->index) >> huge_page_shift(h);

You don't need to use brackets here.  While C's operator precedence is
legendarily confusing, the arrow operator binds far tighter than the
shift operator.