Re: [PATCH v8 06/10] iomap: fix iomap_dio_zero() for fs bs > system page size

Matthew Wilcox
2024-07-02T16:50:24Z

On Tue, Jul 02, 2024 at 02:02:50PM +0200, Christoph Hellwig wrote:
> On Tue, Jul 02, 2024 at 10:15:56AM +0000, Pankaj Raghav (Samsung) wrote:
> > Willy suggested we could use raw pages as we don't need the metadata
> > from using a folio. [0]
>
> Ok, that feels weird but I'll defer to his opinion in that case.

Let me see if I can make you feel less weird about it, since I think
this is something that people should have a clear feeling about.

In the Glorious Future, when we've separated pages and folios from each
other, folios are conceptually memory that gets mapped to userspace.
They have refcounts, mapcounts, a pointer to a file's mapping or an anon
vma's anon_vma, an index within that object, an LRU list, a dirty flag,
a lock bit, and so on.

We don't need any of that here. We might choose to use a special memdesc
for accounting purposes, but there's no need to allocate a folio for it.
For now, leaving it as a plain allocation of pages seems like the smartest
option, and we can revisit in the future.