From 78f11a255749d09025f54d4e2df4fbcb031530e2 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Wed, 27 Apr 2011 15:26:45 -0700 Subject: mm: thp: fix /dev/zero MAP_PRIVATE and vm_flags cleanups The huge_memory.c THP page fault was allowed to run if vm_ops was null (which would succeed for /dev/zero MAP_PRIVATE, as the f_op->mmap wouldn't setup a special vma->vm_ops and it would fallback to regular anonymous memory) but other THP logics weren't fully activated for vmas with vm_file not NULL (/dev/zero has a not NULL vma->vm_file). So this removes the vm_file checks so that /dev/zero also can safely use THP (the other albeit safer approach to fix this bug would have been to prevent the THP initial page fault to run if vm_file was set). After removing the vm_file checks, this also makes huge_memory.c stricter in khugepaged for the DEBUG_VM=y case. It doesn't replace the vm_file check with a is_pfn_mapping check (but it keeps checking for VM_PFNMAP under VM_BUG_ON) because for a is_cow_mapping() mapping VM_PFNMAP should only be allowed to exist before the first page fault, and in turn when vma->anon_vma is null (so preventing khugepaged registration). So I tend to think the previous comment saying if vm_file was set, VM_PFNMAP might have been set and we could still be registered in khugepaged (despite anon_vma was not NULL to be registered in khugepaged) was too paranoid. The is_linear_pfn_mapping check is also I think superfluous (as described by comment) but under DEBUG_VM it is safe to stay. Addresses https://bugzilla.kernel.org/show_bug.cgi?id=33682 Signed-off-by: Andrea Arcangeli Reported-by: Caspar Zhang Acked-by: Mel Gorman Acked-by: Rik van Riel Cc: [2.6.38.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/huge_mm.h | 2 +- include/linux/mm.h | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index df29c8fde36b..8847c8c29791 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -117,7 +117,7 @@ static inline void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long end, long adjust_next) { - if (!vma->anon_vma || vma->vm_ops || vma->vm_file) + if (!vma->anon_vma || vma->vm_ops) return; __vma_adjust_trans_huge(vma, start, end, adjust_next); } diff --git a/include/linux/mm.h b/include/linux/mm.h index 692dbae6ffa7..2348db26bc3d 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -137,7 +137,8 @@ extern unsigned int kobjsize(const void *objp); #define VM_RandomReadHint(v) ((v)->vm_flags & VM_RAND_READ) /* - * special vmas that are non-mergable, non-mlock()able + * Special vmas that are non-mergable, non-mlock()able. + * Note: mm/huge_memory.c VM_NO_THP depends on this definition. */ #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP) -- cgit v1.2.3