Re: Where to put page->memdesc initially

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Sep 02, 2025 at 08:03:57PM +0100, Matthew Wilcox wrote:
> So, page_slab() will first load page->memdesc (the same bits as
> page->lru.prev), check the bottom four bits match the slab memdesc, and
> also check page->page_type matches PGTY_slab.  I don't like this a lot,
> because it's two loads rather than one atomic load, but it should only
> be present for one commit.
> 
> In the next commit, we can separately allocate struct folio, make
> page->memdesc point to struct folio and drop the PGTY_slab check (as
> there will be no more uses of the first tail page for the mapcount stuff).

So to rephrase, there is no great free space for memdesc in struct
page right now, but after the folio is split then it is fine?

Thus you have a few commits within a single series where it is less
efficient?

Seems OK to me..

Jason