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

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

On 9/14/26 15:17, Matthew Wilcox wrote:
> 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.

Confusing indeed.

> 
> 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!

I'd assume Zi will pick up your patches and can massage the patch description to
summarize why folios are awkward here, but that cleaning this up is future work.

-- 
Cheers,

David