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    Subject[PATCH 2/3] make new alloc_pages_exact()
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    What I really wanted in the end was a highmem-capable
    alloc_pages_exact(), so here it is. This function can be used to
    allocate unmapped (like highmem) non-power-of-two-sized areas of
    memory. This is in constast to get_free_pages_exact() which can only
    allocate from lowmem.

    My plan is to use this in the virtio_balloon driver to allocate large,
    oddly-sized contiguous areas.

    The new __alloc_pages_exact() now takes a size in numbers of pages,
    and returns a 'struct page', which means it can now address
    highmem. The (new) argument order mirrors alloc_pages() itself.

    It's a bit unfortunate that this introduces __free_pages_exact()
    alongside 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@linux.vnet.ibm.com>
    ---

    linux-2.6.git-dave/include/linux/gfp.h | 4 +
    linux-2.6.git-dave/mm/page_alloc.c | 85 ++++++++++++++++++++++++---------
    2 files changed, 68 insertions(+), 21 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 2011-04-14 09:14:35.533886248 -0700
    +++ linux-2.6.git-dave/include/linux/gfp.h 2011-04-14 09:14:35.573886242 -0700
    @@ -352,6 +352,10 @@ 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 gfp_mask, unsigned long nr_pages);
    +void __free_pages_exact(struct page *page, unsigned long nr_pages);
    +/* 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 2011-04-14 09:14:35.545886248 -0700
    +++ linux-2.6.git-dave/mm/page_alloc.c 2011-04-14 09:24:48.793504357 -0700
    @@ -2318,9 +2318,10 @@ void free_pages(unsigned long addr, unsi
    EXPORT_SYMBOL(free_pages);

    /**
    - * get_free_pages_exact - allocate an exact number physically-contiguous pages.
    - * @size: the number of bytes to allocate
    + * __alloc_pages_exact - allocate an exact number physically-contiguous pages.
    + * @nr_pages: the number of pages to allocate
    * @gfp_mask: GFP flags for the allocation
    + * returns: struct page for allocated memory
    *
    * This function is similar to alloc_pages(), except that it allocates the
    * minimum number of pages to satisfy the request. alloc_pages() can only
    @@ -2330,29 +2331,76 @@ EXPORT_SYMBOL(free_pages);
    *
    * 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, unsigned long nr_pages)
    {
    - unsigned int order = get_order(size);
    - unsigned long addr;
    + unsigned int order = get_order(nr_pages * PAGE_SIZE);
    + 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 + nr_pages;

    - 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);
    +
    +/**
    + * __free_pages_exact - release memory allocated via __alloc_pages_exact()
    + * @virt: the value returned by get_free_pages_exact.
    + * @nr_pages: size in pages, same value as passed to __alloc_pages_exact().
    + *
    + * Release the memory allocated by a previous call to __alloc_pages_exact().
    + */
    +void __free_pages_exact(struct page *page, unsigned long nr_pages)
    +{
    + struct page *end = page + nr_pages;
    +
    + while (page < end) {
    + __free_page(page);
    + page++;
    + }
    +}
    +EXPORT_SYMBOL(__free_pages_exact);
    +
    +/**
    + * get_free_pages_exact - allocate an exact number physically-contiguous pages.
    + * @gfp_mask: GFP flags for the allocation
    + * @size: the number of bytes to allocate
    + * returns: virtual address of 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
    + * 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 *page;
    + unsigned long nr_pages = PAGE_ALIGN(size) / PAGE_SIZE;
    +
    + /* If we are using page_address(), we can not allow highmem */
    + VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);
    +
    + page = __alloc_pages_exact(gfp_mask, nr_pages);
    + if (page)
    + return (void *) page_address(page);
    + return NULL;
    }
    EXPORT_SYMBOL(get_free_pages_exact);

    /**
    - * free_pages_exact - release memory allocated via get_free_pages_exact()
    + * __free_pages_exact - release memory allocated via get_free_pages_exact()
    * @virt: the value returned by get_free_pages_exact.
    * @size: size of allocation, same value as passed to get_free_pages_exact().
    *
    @@ -2360,13 +2408,8 @@ EXPORT_SYMBOL(get_free_pages_exact);
    */
    void free_pages_exact(void *virt, size_t size)
    {
    - unsigned long addr = (unsigned long)virt;
    - unsigned long end = addr + PAGE_ALIGN(size);
    -
    - while (addr < end) {
    - free_page(addr);
    - addr += PAGE_SIZE;
    - }
    + int nr_pages = PAGE_ALIGN(size)/PAGE_SIZE;
    + __free_pages_exact(virt_to_page(virt), nr_pages);
    }
    EXPORT_SYMBOL(free_pages_exact);

    diff -puN mm/swap.c~make_new_alloc_pages_exact mm/swap.c
    diff -puN tools/virtio/linux/virtio.h~make_new_alloc_pages_exact tools/virtio/linux/virtio.h
    diff -puN include/linux/types.h~make_new_alloc_pages_exact include/linux/types.h
    diff -puN Documentation/kbuild/kbuild.txt~make_new_alloc_pages_exact Documentation/kbuild/kbuild.txt
    diff -puN Documentation/sparse.txt~make_new_alloc_pages_exact Documentation/sparse.txt
    _

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