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authorLee Schermerhorn <Lee.Schermerhorn@hp.com>2007-11-14 16:59:10 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-11-14 18:45:38 -0800
commit3ad33b2436b545cbe8b28e53f3710432cad457ab (patch)
tree581808f90a08838ee27d76cc24812c7093c216a9 /mm/mempolicy.c
parente1a1c997afe907e6ec4799e4be0f38cffd8b418c (diff)
Migration: find correct vma in new_vma_page()
We hit the BUG_ON() in mm/rmap.c:vma_address() when trying to migrate via mbind(MPOL_MF_MOVE) a non-anon region that spans multiple vmas. For anon-regions, we just fail to migrate any pages beyond the 1st vma in the range. This occurs because do_mbind() collects a list of pages to migrate by calling check_range(). check_range() walks the task's mm, spanning vmas as necessary, to collect the migratable pages into a list. Then, do_mbind() calls migrate_pages() passing the list of pages, a function to allocate new pages based on vma policy [new_vma_page()], and a pointer to the first vma of the range. For each page in the list, new_vma_page() calls page_address_in_vma() passing the page and the vma [first in range] to obtain the address to get for alloc_page_vma(). The page address is needed to get interleaving policy correct. If the pages in the list come from multiple vmas, eventually, new_page_address() will pass that page to page_address_in_vma() with the incorrect vma. For !PageAnon pages, this will result in a bug check in rmap.c:vma_address(). For anon pages, vma_address() will just return EFAULT and fail the migration. This patch modifies new_vma_page() to check the return value from page_address_in_vma(). If the return value is EFAULT, new_vma_page() searchs forward via vm_next for the vma that maps the page--i.e., that does not return EFAULT. This assumes that the pages in the list handed to migrate_pages() is in address order. This is currently case. The patch documents this assumption in a new comment block for new_vma_page(). If new_vma_page() cannot locate the vma mapping the page in a forward search in the mm, it will pass a NULL vma to alloc_page_vma(). This will result in the allocation using the task policy, if any, else system default policy. This situation is unlikely, but the patch documents this behavior with a comment. Note, this patch results in restarting from the first vma in a multi-vma range each time new_vma_page() is called. If this is not acceptable, we can make the vma argument a pointer, both in new_vma_page() and it's caller unmap_and_move() so that the value held by the loop in migrate_pages() always passes down the last vma in which a page was found. This will require changes to all new_page_t functions passed to migrate_pages(). Is this necessary? For this patch to work, we can't bug check in vma_address() for pages outside the argument vma. This patch removes the BUG_ON(). All other callers [besides new_vma_page()] already check the return status. Tested on x86_64, 4 node NUMA platform. Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com> Acked-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mempolicy.c')
-rw-r--r--mm/mempolicy.c21
1 files changed, 19 insertions, 2 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index c1592a94582..83c69f8a64c 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -722,12 +722,29 @@ out:
}
+/*
+ * Allocate a new page for page migration based on vma policy.
+ * Start assuming that page is mapped by vma pointed to by @private.
+ * Search forward from there, if not. N.B., this assumes that the
+ * list of pages handed to migrate_pages()--which is how we get here--
+ * is in virtual address order.
+ */
static struct page *new_vma_page(struct page *page, unsigned long private, int **x)
{
struct vm_area_struct *vma = (struct vm_area_struct *)private;
+ unsigned long uninitialized_var(address);
- return alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma,
- page_address_in_vma(page, vma));
+ while (vma) {
+ address = page_address_in_vma(page, vma);
+ if (address != -EFAULT)
+ break;
+ vma = vma->vm_next;
+ }
+
+ /*
+ * if !vma, alloc_page_vma() will use task or system default policy
+ */
+ return alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
}
#else