Messages in this thread |  | | Date | Tue, 3 Sep 2019 05:11:55 -0700 | From | Matthew Wilcox <> | Subject | Re: [PATCH v5 1/2] mm: Allow the page cache to allocate large pages |
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On Tue, Sep 03, 2019 at 01:57:48PM +0200, Michal Hocko wrote: > On Mon 02-09-19 03:23:40, William Kucharski wrote: > > Add an 'order' argument to __page_cache_alloc() and > > do_read_cache_page(). Ensure the allocated pages are compound pages. > > Why do we need to touch all the existing callers and change them to use > order 0 when none is actually converted to a different order? This just > seem to add a lot of code churn without a good reason. If anything I > would simply add __page_cache_alloc_order and make __page_cache_alloc > call it with order 0 argument.
Patch 2/2 uses a non-zero order. I agree it's a lot of churn without good reason; that's why I tried to add GFP_ORDER flags a few months ago. Unfortunately, you didn't like that approach either.
> Also is it so much to ask callers to provide __GFP_COMP explicitly?
Yes, it's an unreasonable burden on the callers. Those that pass 0 will have the test optimised away by the compiler (for the non-NUMA case). For the NUMA case, passing zero is going to be only a couple of extra instructions to not set the GFP_COMP flag.
> > #ifdef CONFIG_NUMA > > -extern struct page *__page_cache_alloc(gfp_t gfp); > > +extern struct page *__page_cache_alloc(gfp_t gfp, unsigned int order); > > #else > > -static inline struct page *__page_cache_alloc(gfp_t gfp) > > +static inline struct page *__page_cache_alloc(gfp_t gfp, unsigned int order) > > { > > - return alloc_pages(gfp, 0); > > + if (order > 0) > > + gfp |= __GFP_COMP; > > + return alloc_pages(gfp, order); > > } > > #endif
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