Messages in this thread | | | Subject | Re: [PATCH] Add alloc_pages_exact() and free_pages_exact() | From | Dave Hansen <> | Date | Tue, 24 Jun 2008 14:33:38 -0700 |
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On Tue, 2008-06-24 at 11:40 -0500, Timur Tabi wrote: > +void *alloc_pages_exact(size_t size, gfp_t gfp_mask) > +{ > + unsigned int order = get_order(size); > + unsigned long addr; > + > + addr = __get_free_pages(gfp_mask, order); > + if (addr) { > + unsigned long alloc_end = addr + (PAGE_SIZE << order); > + unsigned long used = addr + PAGE_ALIGN(size); > + > + split_page(virt_to_page(addr), order); > + while (used < alloc_end) { > + free_page(used); > + used += PAGE_SIZE; > + } > + } > + > + return (void *)addr; > +}
Hi Timur,
This looks like a really good idea. It looks pretty good to me, no functional problems. My brain had a really hard time parsing that code for some reason, though. Could just be a lack of coffee.
I think the thing that confused me was trying to figure out if 'alloc_end' was the end of what we *did* allocate from __get_free_pages() or if it was the *goal* allocation end.
'used' also seemed like a slightly strange variable name because it points to the memory which is about to be freed and ends up *unused*.
I'll offer this up just in case you like it better. For me, it is easier to parse, and should do the exact same thing. I also think it's slightly nicer to do the arithmetic on 'struct page *' rather than vaddrs in 'unsigned long'. It is _slightly_ cheaper not having to do a virt_to_page() on each free_page() call. The same would go for the free side as well.
All of the 'struct page *' arithmetic is OK since it is all done inside one MAX_ORDER area.
void *alloc_pages_exact(size_t size, gfp_t gfp_mask) { unsigned int order = get_order(size); void *alloc; struct page *surplus_start; struct page *surplus_end; struct page *page;
size = PAGE_ALIGN(size);
alloc = (void *)__get_free_pages(gfp_mask, order); if (!alloc) return NULL;
/* Turn the big allocation into a bunch of single pages */ split_page(virt_to_page(alloc), order);
surplus_start = virt_to_page(alloc + size); surplus_end = surplus_start + (1 << order);
for (page = surplus_start; page < surplus_end; page++) __free_page(page);
return alloc; }
-- Dave
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