Re: [RFC 00/11] Remove 'order' argument from many mm functions

Matthew Wilcox
2019-05-09T14:07:16Z

On Wed, May 08, 2019 at 06:58:09PM -0700, Ira Weiny wrote:
> On Mon, May 06, 2019 at 09:05:58PM -0700, Matthew Wilcox wrote:
> > It's possible to save a few hundred bytes from the kernel text by moving
> > the 'order' argument into the GFP flags. I had the idea while I was
> > playing with THP pagecache (notably, I didn't want to add an 'order'
> > parameter to pagecache_get_page())
...
> > Anyway, this is just a quick POC due to me being on an aeroplane for
> > most of today. Maybe we don't want to spend five GFP bits on this.
> > Some bits of this could be pulled out and applied even if we don't want
> > to go for the main objective. eg rmqueue_pcplist() doesn't use its
> > gfp_flags argument.
>
> Over all I may just be a simpleton WRT this but I'm not sure that the added
> complexity justifies the gain.

I'm disappointed that you see it as added complexity. I see it as
reducing complexity. With this patch, we can simply pass GFP_PMD as
a flag to pagecache_get_page(); without it, we have to add a fifth
parameter to pagecache_get_page() and change all the callers to pass '0'.