Re: [PATCH v4 7/9] filemap: Allow __filemap_get_folio to allocate large folios

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On Thu, Jul 13, 2023 at 03:42:18PM +0100, Matthew Wilcox wrote:
> On Thu, Jul 13, 2023 at 01:04:39AM -0400, Kent Overstreet wrote:
> > On Mon, Jul 10, 2023 at 02:02:51PM +0100, Matthew Wilcox (Oracle) wrote:
> > > Allow callers of __filemap_get_folio() to specify a preferred folio
> > > order in the FGP flags.  This is only honoured in the FGP_CREATE path;
> > > if there is already a folio in the page cache that covers the index,
> > > we will return it, no matter what its order is.  No create-around is
> > > attempted; we will only create folios which start at the specified index.
> > > Unmodified callers will continue to allocate order 0 folios.
> > 
> > Why not just add an end_index parameter to filemap_get_folio()?
> 
> I'm reluctant to add more parameters.  Aside from the churn, every extra
> parameter makes the function that little bit harder to use.  I like this
> encoding; users who don't know/care about it get the current default
> behaviour, and it's a simple addition to the users who do want to care.
> end_index is particularly tricky ... what if it's lower than index?

But we're refactoring all this code (and chaning our thinking) to
extents/ranges, not blocks - I'd say end_index is more natural in the
long run.

Plus, it lets us put the logic for "how big of a folio do we want to
allocate" in one place.

(end_index < index is just a BUG_ON()).



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