Re: [PATCH v9 14/15] filemap: Add support for authoritative mappings

["David Hildenbrand (Arm)" <david@kernel.org>]

On 8/5/26 23:05, Matthew Wilcox (Oracle) wrote:
> An authoritative mapping knows about all the folios in the mapping.
> If read() finds a missing folio, there's no reason to allocate one and
> try to read it because we know it's a zero region of the file.  We can
> just call iov_iter_zero() instead.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Jane Chu <jane.chu@oracle.com>
> ---
>  include/linux/pagemap.h | 11 +++++++++++
>  mm/filemap.c            | 18 ++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 968b791cfd14..22d48935ffda 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -210,6 +210,7 @@ enum mapping_flags {
>  	AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM = 9,
>  	AS_KERNEL_FILE = 10,	/* mapping for a fake kernel file that shouldn't
>  				   account usage to user cgroups */
> +	AS_AUTHORITATIVE = 11,	/* If we miss in the page cache, it's a hole */

Just curious if "in-memory file system" would be a different way of looking at
it. There, a hole in the page cache always expresses a hole in the file.

	AS_IN_MEMORY_FILE

Just an idea, because that's why I always had in mind regarding that (all state
in memory).

-- 
Cheers,

David