[RFC PATCH v4 7/8] hugetlb: create hugetlb_unmap_file_folio to unmap single file folio

Mike Kravetz
2022-07-06T20:25:16Z

Create the new routine hugetlb_unmap_file_folio that will unmap a single
file folio. This is refactored code from hugetlb_vmdelete_list. It is
modified to do locking within the routine itself and check whether the
page is mapped within a specific vma before unmapping.

This refactoring will be put to use and expanded upon in a subsequent
patch adding vma specific locking.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
fs/hugetlbfs/inode.c | 124 +++++++++++++++++++++++++++++++++----------
1 file changed, 95 insertions(+), 29 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 31bd4325fce5..0eac0ea2a245 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -396,6 +396,94 @@ static int hugetlbfs_write_end(struct file *file, struct address_space *mapping,
return -EINVAL;
}

+/*
+ * Called with i_mmap_rwsem held for inode based vma maps. This makes
+ * sure vma (and vm_mm) will not go away. We also hold the hugetlb fault
+ * mutex for the page in the mapping. So, we can not race with page being
+ * faulted into the vma.
+ */
+static bool hugetlb_vma_maps_page(struct vm_area_struct *vma,
+ unsigned long addr, struct page *page)
+{
+ pte_t *ptep, pte;
+
+ ptep = huge_pte_offset(vma->vm_mm, addr,
+ huge_page_size(hstate_vma(vma)));
+
+ if (!ptep)
+ return false;
+
+ pte = huge_ptep_get(ptep);
+ if (huge_pte_none(pte) || !pte_present(pte))
+ return false;
+
+ if (pte_page(pte) == page)
+ return true;
+
+ return false; /* WTH??? */
+}
+
+/*
+ * Can vma_offset_start/vma_offset_end overflow on 32-bit arches?
+ * No, because the interval tree returns us only those vmas
+ * which overlap the truncated area starting at pgoff,
+ * and no vma on a 32-bit arch can span beyond the 4GB.
+ */
+static unsigned long vma_offset_start(struct vm_area_struct *vma, pgoff_t start)
+{
+ if (vma->vm_pgoff < start)
+ return (start - vma->vm_pgoff) << PAGE_SHIFT;
+ else
+ return 0;
+}
+
+static unsigned long vma_offset_end(struct vm_area_struct *vma, pgoff_t end)
+{
+ unsigned long t_end;
+
+ if (!end)
+ return vma->vm_end;
+
+ t_end = ((end - vma->vm_pgoff) << PAGE_SHIFT) + vma->vm_start;
+ if (t_end > vma->vm_end)
+ t_end = vma->vm_end;
+ return t_end;
+}
+
+/*
+ * Called with hugetlb fault mutex held. Therefore, no more mappings to
+ * this folio can be created while executing the routine.
+ */
+static void hugetlb_unmap_file_folio(struct hstate *h,
+ struct address_space *mapping,
+ struct folio *folio, pgoff_t index)
+{
+ struct rb_root_cached *root = &mapping->i_mmap;
+ struct page *page = &folio->page;
+ struct vm_area_struct *vma;
+ unsigned long v_start;
+ unsigned long v_end;
+ pgoff_t start, end;
+
+ start = index * pages_per_huge_page(h);
+ end = ((index + 1) * pages_per_huge_page(h));
+
+ i_mmap_lock_write(mapping);
+
+ vma_interval_tree_foreach(vma, root, start, end - 1) {
+ v_start = vma_offset_start(vma, start);
+ v_end = vma_offset_end(vma, end);
+
+ if (!hugetlb_vma_maps_page(vma, vma->vm_start + v_start, page))
+ continue;
+
+ unmap_hugepage_range(vma, vma->vm_start + v_start, v_end,
+ NULL, ZAP_FLAG_DROP_MARKER);
+ }
+
+ i_mmap_unlock_write(mapping);
+}
+
static void
hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
zap_flags_t zap_flags)
@@ -408,30 +496,13 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
* an inclusive "last".
*/
vma_interval_tree_foreach(vma, root, start, end ? end - 1 : ULONG_MAX) {
- unsigned long v_offset;
+ unsigned long v_start;
unsigned long v_end;

- /*
- * Can the expression below overflow on 32-bit arches?
- * No, because the interval tree returns us only those vmas
- * which overlap the truncated area starting at pgoff,
- * and no vma on a 32-bit arch can span beyond the 4GB.
- */
- if (vma->vm_pgoff < start)
- v_offset = (start - vma->vm_pgoff) << PAGE_SHIFT;
- else
- v_offset = 0;
-
- if (!end)
- v_end = vma->vm_end;
- else {
- v_end = ((end - vma->vm_pgoff) << PAGE_SHIFT)
- + vma->vm_start;
- if (v_end > vma->vm_end)
- v_end = vma->vm_end;
- }
+ v_start = vma_offset_start(vma, start);
+ v_end = vma_offset_end(vma, end);

- unmap_hugepage_range(vma, vma->vm_start + v_offset, v_end,
+ unmap_hugepage_range(vma, vma->vm_start + v_start, v_end,
NULL, zap_flags);
}
}
@@ -504,14 +575,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
* the fault mutex. The mutex will prevent faults
* until we finish removing the folio.
*/
- if (unlikely(folio_mapped(folio))) {
- i_mmap_lock_write(mapping);
- hugetlb_vmdelete_list(&mapping->i_mmap,
- index * pages_per_huge_page(h),
- (index + 1) * pages_per_huge_page(h),
- ZAP_FLAG_DROP_MARKER);
- i_mmap_unlock_write(mapping);
- }
+ if (unlikely(folio_mapped(folio)))
+ hugetlb_unmap_file_folio(h, mapping, folio,
+ index);

folio_lock(folio);
/*
--
2.35.3