Re: [PATCH 04/23] ocfs2: Use a folio in ocfs2_zero_new_buffers()

[Matthew Wilcox <willy@infradead.org>]

On Sat, Dec 14, 2024 at 10:01:20PM +0800, Joseph Qi wrote:
> > -static void ocfs2_zero_new_buffers(struct folio *folio, unsigned from, unsigned to)
> > +static void ocfs2_zero_new_buffers(struct folio *folio, size_t from, size_t to)
> 
> Don't see why we have to change 'unsigned' to 'size_t'.

This is just part of the folio conversion process.  Three reasons:

1. size_t is an indication to the human reader that this is a count of the
number of bytes in memory, as opposed to anything else that an 'unsigned
int' might be.

2. Prepares us for folios which are larger than 2GB in size.  Yes, not
likely to be something that ocfs2 ever supports, but on arm64 with a
16KiB page size, hugetlbfs at the PUD level has folios which are 64GB in
size.  So we need to use size_t within the mm & vfs, and we should
continue that into filesystems.

3. It's actually more efficient.  The CPU has to insert a lot of
zero-extend instructions when calling core code which is using size_t.