Re: [PATCH v2 5/7] filemap: Allow __filemap_get_folio to allocate large folios

Matthew Wilcox
2023-06-04T21:48:53Z

On Sun, Jun 04, 2023 at 11:09:25AM -0700, Darrick J. Wong wrote:
> On Fri, Jun 02, 2023 at 11:24:42PM +0100, Matthew Wilcox (Oracle) wrote:
> > + do {
> > + err = -ENOMEM;
> > + if (order == 1)
> > + order = 0;
>
> Doesn't this interrupt the scale-down progression 2M -> 1M -> 512K ->
> 256K -> 128K -> 64K -> 32K -> 16K -> 4k? What if I want 8k folios?

You can't have order-1 file/anon folios. We have deferred_list in the
third page, so we have to have at least three pages in every large folio.
I forget exactly what it's used for; maybe there's a way to do without
it, but for now that's the rule.