linux-kernel - Re: [PATCH 2/2] mm/huge_memory: cap max length on debugfs file entry folio split

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Message-ID: <AB2FFCD8-6A5B-4E0B-BFE1-4EACC996CA22@nvidia.com>
Date: Wed, 24 Apr 2024 21:05:04 -0400
From: Zi Yan <ziy@...dia.com>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, fstests@...r.kernel.org,
 linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, willy@...radead.org,
 hare@...e.de, john.g.garry@...cle.com, p.raghav@...sung.com,
 da.gomez@...sung.com
Subject: Re: [PATCH 2/2] mm/huge_memory: cap max length on debugfs file entry
 folio split

On 24 Apr 2024, at 18:54, Luis Chamberlain wrote:

> Don't allow to query beyond a mapped file's length. Since this is just
> a debugfs interface allow userspace to be lazy and use a large value so
> we can just use the entire file.
>
> Without this we can end up wasting cycles looking for folios which
> just don't exist for no good reason.
>
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  mm/huge_memory.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8386d24a163e..86a8c7b3b8dc 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3535,7 +3535,7 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
>  	struct file *candidate;
>  	struct address_space *mapping;
>  	int ret = -EINVAL;
> -	pgoff_t index;
> +	pgoff_t index, fsize;
>  	int nr_pages = 1;
>  	unsigned long total = 0, split = 0;
>
> @@ -3547,11 +3547,14 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
>  	if (IS_ERR(candidate))
>  		goto out;
>
> +	mapping = candidate->f_mapping;
> +	fsize = i_size_read(mapping->host);
> +	if (off_end > fsize)
> +		off_end = fsize;
> +
>  	pr_debug("split file-backed THPs in file: %s, page offset: [0x%lx - 0x%lx]\n",
>  		 file_path, off_start, off_end);
>
> -	mapping = candidate->f_mapping;
> -
>  	for (index = off_start; index < off_end; index += nr_pages) {
>  		struct folio *folio = filemap_get_folio(mapping, index);

LGTM. Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi

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