Date:2010-04-14 23:59:28 (12 years 5 months ago)
Author:Rik van Riel
Commit:e8a03feb54ca7f1768bbdc2b491f9ef654e6d01d
Message:rmap: add exclusively owned pages to the newest anon_vma

The recent anon_vma fixes cause many anonymous pages to end up
in the parent process anon_vma, even when the page is exclusively
owned by the current process.

Adding exclusively owned anonymous pages to the top anon_vma
reduces rmap scanning overhead, especially in workloads with
forking servers.

This patch adds a parameter to __page_set_anon_rmap that can
be used to indicate whether or not the added page is exclusively
owned by the current process.

Pages added through page_add_new_anon_rmap are exclusively
owned by the current process, and can be added to the top
anon_vma.

Pages added through page_add_anon_rmap can be either shared
or exclusively owned, so we do the conservative thing and
add it to the oldest anon_vma.

A next step would be to add the exclusive parameter to
page_add_anon_rmap, to be used from functions where we do
know for sure whether a page is exclusively owned.

Signed-off-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Lightly-tested-by: Borislav Petkov <bp@alien8.de>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
[ Edited to look nicer - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Files: mm/rmap.c (3 diffs)

Change Details

mm/rmap.c
730730 * @page: the page to add the mapping to
731731 * @vma: the vm area in which the mapping is added
732732 * @address: the user virtual address mapped
733 * @exclusive: the page is exclusively owned by the current process
733734 */
734735static void __page_set_anon_rmap(struct page *page,
735    struct vm_area_struct *vma, unsigned long address)
736    struct vm_area_struct *vma, unsigned long address, int exclusive)
736737{
737    struct anon_vma_chain *avc;
738    struct anon_vma *anon_vma;
738    struct anon_vma *anon_vma = vma->anon_vma;
739739
740    BUG_ON(!vma->anon_vma);
740    BUG_ON(!anon_vma);
741741
742742    /*
743     * We must use the _oldest_ possible anon_vma for the page mapping!
743     * If the page isn't exclusively mapped into this vma,
744     * we must use the _oldest_ possible anon_vma for the
745     * page mapping!
744746     *
745     * So take the last AVC chain entry in the vma, which is the deepest
746     * ancestor, and use the anon_vma from that.
747     * So take the last AVC chain entry in the vma, which is
748     * the deepest ancestor, and use the anon_vma from that.
747749     */
748    avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma);
749    anon_vma = avc->anon_vma;
750    if (!exclusive) {
751        struct anon_vma_chain *avc;
752        avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma);
753        anon_vma = avc->anon_vma;
754    }
750755
751756    anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
752757    page->mapping = (struct address_space *) anon_vma;
...... 
802807    VM_BUG_ON(!PageLocked(page));
803808    VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
804809    if (first)
805        __page_set_anon_rmap(page, vma, address);
810        __page_set_anon_rmap(page, vma, address, 0);
806811    else
807812        __page_check_anon_rmap(page, vma, address);
808813}
...... 
824829    SetPageSwapBacked(page);
825830    atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
826831    __inc_zone_page_state(page, NR_ANON_PAGES);
827    __page_set_anon_rmap(page, vma, address);
832    __page_set_anon_rmap(page, vma, address, 1);
828833    if (page_evictable(page, vma))
829834        lru_cache_add_lru(page, LRU_ACTIVE_ANON);
830835    else

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