Re: [PATCH 1/3] md: Use folio_alloc_buffers()

[Matthew Wilcox <willy@infradead.org>]

On Mon, Sep 14, 2026 at 03:12:31PM +0200, David Hildenbrand (Arm) wrote:
> On 9/14/26 06:18, Matthew Wilcox (Oracle) wrote:
> > Remove the last user of alloc_page_buffers().  This isn't _great_,
> 
> You should tell us "why" this isn't great.
> 
> Because we're allocating folios although these things are not actually folios? I
> can only speculate :)

Well, we actually aren't allocating folios in md-bitmap:

        for ( ; pnum < num_pages; pnum++) {
                store->filemap[pnum] = alloc_page(GFP_KERNEL|__GFP_ZERO);

and it's not clear to me that we should be allocating folios; they're
internal memory to the md-bitmap code that are never mapped to userspace,
nor enter the page cache.  But they do have buffer heads attached to them.

The md-bitmap code probably needs to be rewritten to not use buffer heads
at all, but then I hear from some people that it's scheduled for deletion,
so don't spend any time on it.  But I can't find anything official about
that anywhere.

> Code itself looks good.

Thanks!