On Thu, 7 Apr 2011, Dave Hansen wrote:
>
> What I really wanted in the end was a highmem-capable alloc_pages_exact(),
> so here it is.
>
Perhaps expand upon how the new alloc_pages_exact() works and what it will
be used for instead of only talking about how it's named?
> It's a bit unfortunate that we have __free_pages_exact() and
> free_pages_exact(), but that mess already exists with __free_pages()
> vs. free_pages_exact(). So, at worst, this mirrors the mess that we
> already have.
>
> I'm also a bit worried that I've not put in something named
> alloc_pages_exact(), but that behaves differently than it did before this
> set. I got all of the in-tree cases, but I'm a bit worried about
> stragglers elsewhere. So, I'm calling this __alloc_pages_exact() for
> the moment. We can take out the __ some day if it bothers people.
>
> Note that the __get_free_pages() has a !GFP_HIGHMEM check. Now that
> we are using alloc_pages_exact() instead of __get_free_pages() for
> get_free_pages_exact(), we had to add a new check in
> get_free_pages_exact().
>
> This has been compile and boot tested, and I checked that
>
> echo 2 > /sys/kernel/profiling
>
> still works, since it uses get_free_pages_exact().
>
> Signed-off-by: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>
> ---
>
> linux-2.6.git-dave/drivers/video/pxafb.c | 4 -
> linux-2.6.git-dave/include/linux/gfp.h | 4 +
> linux-2.6.git-dave/kernel/profile.c | 4 -
> linux-2.6.git-dave/mm/page_alloc.c | 81 +++++++++++++++++++++++--------
> 4 files changed, 69 insertions(+), 24 deletions(-)
>
> diff -puN include/linux/gfp.h~make_new_alloc_pages_exact include/linux/gfp.h
> --- linux-2.6.git/include/linux/gfp.h~make_new_alloc_pages_exact 2011-04-07 08:41:08.158387017 -0700
> +++ linux-2.6.git-dave/include/linux/gfp.h 2011-04-07 08:41:08.174387016 -0700
> @@ -351,6 +351,10 @@ extern struct page *alloc_pages_vma(gfp_
> extern unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order);
> extern unsigned long get_zeroed_page(gfp_t gfp_mask);
>
> +/* 'struct page' version */
> +struct page *__alloc_pages_exact(gfp_t, size_t);
> +void __free_pages_exact(struct page *, size_t);
They're not required, but these should have the names of the arguments
like the other prototypes in this file.
> +/* virtual address version */
> void *get_free_pages_exact(gfp_t gfp_mask, size_t size);
> void free_pages_exact(void *virt, size_t size);
>
> diff -puN mm/page_alloc.c~make_new_alloc_pages_exact mm/page_alloc.c
> --- linux-2.6.git/mm/page_alloc.c~make_new_alloc_pages_exact 2011-04-07 08:41:08.162387016 -0700
> +++ linux-2.6.git-dave/mm/page_alloc.c 2011-04-07 09:44:33.937537711 -0700
> @@ -2318,36 +2318,83 @@ void free_pages(unsigned long addr, unsi
> EXPORT_SYMBOL(free_pages);
>
> /**
> - * get_free_pages_exact - allocate an exact number physically-contiguous pages.
> + * __alloc_pages_exact - allocate an exact number physically-contiguous pages.
> * @gfp_mask: GFP flags for the allocation
> * @size: the number of bytes to allocate
> + * returns: struct page for allocated memory
> *
> - * This function is similar to __get_free_pages(), except that it allocates the
> - * minimum number of pages to satisfy the request. get_free_pages() can only
> + * This function is similar to alloc_pages(), except that it allocates the
> + * minimum number of pages to satisfy the request. alloc_pages() can only
> * allocate memory in power-of-two pages.
> *
> * This function is also limited by MAX_ORDER.
> *
> * Memory allocated by this function must be released by free_pages_exact().
> */
> -void *get_free_pages_exact(gfp_t gfp_mask, size_t size)
> +struct page *__alloc_pages_exact(gfp_t gfp_mask, size_t size)
> {
> unsigned int order = get_order(size);
> - unsigned long addr;
> + struct page *page;
>
> - addr = __get_free_pages(gfp_mask, order);
> - if (addr) {
> - unsigned long alloc_end = addr + (PAGE_SIZE << order);
> - unsigned long used = addr + PAGE_ALIGN(size);
> + page = alloc_pages(gfp_mask, order);
> + if (page) {
> + struct page *alloc_end = page + (1 << order);
> + struct page *used = page + PAGE_ALIGN(size)/PAGE_SIZE;
Wouldn't it better to call this "unused" rather than "used" since it
represents a cursor over pages that we want to free?
>
> - split_page(virt_to_page((void *)addr), order);
> + split_page(page, order);
> while (used < alloc_end) {
> - free_page(used);
> - used += PAGE_SIZE;
> + __free_page(used);
> + used++;
> }
> }
>
> - return (void *)addr;
> + return page;
> +}
> +EXPORT_SYMBOL(__alloc_pages_exact);
--
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