[PATCH v6 6/6] uprobe: collapse THP pmd after removing all uprobes

[Song Liu <songliubraving@fb.com>]

After all uprobes are removed from the huge page (with PTE pgtable), it
is possible to collapse the pmd and benefit from THP again. This patch
does the collapse by setting AS_COLLAPSE_PMD. khugepage would retrace
the page table.

A check for vma->anon_vma is removed from retract_page_tables(). The
check was initially marked as "probably overkill". The code works well
without the check.

An issue on earlier version was discovered by kbuild test robot.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 kernel/events/uprobes.c | 6 +++++-
 mm/khugepaged.c         | 3 ---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index a20d7b43a056..418382259f61 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -474,6 +474,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	struct page *old_page, *new_page;
 	struct vm_area_struct *vma;
 	int ret, is_register, ref_ctr_updated = 0;
+	struct page *orig_page = NULL;
 
 	is_register = is_swbp_insn(&opcode);
 	uprobe = container_of(auprobe, struct uprobe, arch);
@@ -512,7 +513,6 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	copy_to_page(new_page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
 
 	if (!is_register) {
-		struct page *orig_page;
 		pgoff_t index;
 
 		index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT;
@@ -540,6 +540,10 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	if (ret && is_register && ref_ctr_updated)
 		update_ref_ctr(uprobe, mm, -1);
 
+	if (!ret && orig_page && PageTransCompound(orig_page))
+		set_bit(AS_COLLAPSE_PMD,
+			&compound_head(orig_page)->mapping->flags);
+
 	return ret;
 }
 
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 9b980327fd9b..2e277a2d731f 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1302,9 +1302,6 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff,
 
 	i_mmap_lock_write(mapping);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
-		/* probably overkill */
-		if (vma->anon_vma)
-			continue;
 		addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
 		if (addr & ~HPAGE_PMD_MASK)
 			continue;
-- 
2.17.1