On Wednesday 05 April 2017 08:29 AM, Alexey Kardashevskiy wrote:
On 04/04/17 19:26, Aneesh Kumar K.V wrote:
Alexey Kardashevskiy <a...@ozlabs.ru> writes:
The CMA pages migration code does not support compound pages at
the moment so it performs few tests before proceeding to actual page
migration.
One of the tests - PageTransHuge() - has VM_BUG_ON_PAGE(PageTail()) as
it should be called on head pages. Since we also test for PageCompound(),
and it contains PageTail(), we can simply move PageCompound() in front
of PageTransHuge() and therefore avoid possible VM_BUG_ON_PAGE.
Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
Some of actual POWER8 systems do crash on that BUG_ON.
---
arch/powerpc/mm/mmu_context_iommu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/mm/mmu_context_iommu.c
b/arch/powerpc/mm/mmu_context_iommu.c
index 497130c5c742..ba7fccf993b3 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -81,7 +81,7 @@ struct page *new_iommu_non_cma_page(struct page *page,
unsigned long private,
gfp_t gfp_mask = GFP_USER;
struct page *new_page;
- if (PageHuge(page) || PageTransHuge(page) || PageCompound(page))
+ if (PageCompound(page) || PageHuge(page) || PageTransHuge(page))
A checked for compound page should be sufficient here, because a
Huge/TransHuge page is also marked compound.
But PageCompound() calls PageTail() so PageTail() will be called on a trans
page which is BUG_ON in PageTransHuge but it is not in PageCompound() -
this inconsistency is bothering me. Does not this BUG_ON tell us that we
should not be calling PageTail() on _any_ page?
In other words, should I get a head page (via compound_head()) first and
only then test the head page if it is thp/huge (as you suggested in a chat)?
I was suggesting to replace that if () condition with just
/* We don't handle hugetlb/THP pages yet */
if (PageCompund(page)) {
}
-aneesh
