[PATCH v2 4/9] hugetlb: create remove_inode_single_folio to remove single file folio

Mike Kravetz
2022-09-14T22:19:32Z

Create the new routine remove_inode_single_folio that will remove a
single folio from a file. This is refactored code from
remove_inode_hugepages. It checks for the uncommon case in which the
folio is still mapped and unmaps.

No functional change. This refactoring will be put to use and expanded
upon in a subsequent patches.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
fs/hugetlbfs/inode.c | 105 ++++++++++++++++++++++++++-----------------
1 file changed, 63 insertions(+), 42 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index edd69cc43ca5..7112a9a9f54d 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -411,6 +411,60 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
}
}

+/*
+ * Called with hugetlb fault mutex held.
+ * Returns true if page was actually removed, false otherwise.
+ */
+static bool remove_inode_single_folio(struct hstate *h, struct inode *inode,
+ struct address_space *mapping,
+ struct folio *folio, pgoff_t index,
+ bool truncate_op)
+{
+ bool ret = false;
+
+ /*
+ * If folio is mapped, it was faulted in after being
+ * unmapped in caller. Unmap (again) while holding
+ * 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);
+ }
+
+ folio_lock(folio);
+ /*
+ * After locking page, make sure mapping is the same.
+ * We could have raced with page fault populate and
+ * backout code.
+ */
+ if (folio_mapping(folio) == mapping) {
+ /*
+ * We must remove the folio from page cache before removing
+ * the region/ reserve map (hugetlb_unreserve_pages). In
+ * rare out of memory conditions, removal of the region/reserve
+ * map could fail. Correspondingly, the subpool and global
+ * reserve usage count can need to be adjusted.
+ */
+ VM_BUG_ON(HPageRestoreReserve(&folio->page));
+ hugetlb_delete_from_page_cache(&folio->page);
+ ret = true;
+ if (!truncate_op) {
+ if (unlikely(hugetlb_unreserve_pages(inode, index,
+ index + 1, 1)))
+ hugetlb_fix_reserve_counts(inode);
+ }
+ }
+
+ folio_unlock(folio);
+ return ret;
+}
+
/*
* remove_inode_hugepages handles two distinct cases: truncation and hole
* punch. There are subtle differences in operation for each case.
@@ -418,11 +472,10 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
* truncation is indicated by end of range being LLONG_MAX
* In this case, we first scan the range and release found pages.
* After releasing pages, hugetlb_unreserve_pages cleans up region/reserve
- * maps and global counts. Page faults can not race with truncation
- * in this routine. hugetlb_no_page() prevents page faults in the
- * truncated range. It checks i_size before allocation, and again after
- * with the page table lock for the page held. The same lock must be
- * acquired to unmap a page.
+ * maps and global counts. Page faults can race with truncation.
+ * During faults, hugetlb_no_page() checks i_size before page allocation,
+ * and again after obtaining page table lock. It will 'back out'
+ * allocations in the truncated range.
* hole punch is indicated if end is not LLONG_MAX
* In the hole punch case we scan the range and release found pages.
* Only when releasing a page is the associated region/reserve map
@@ -456,44 +509,12 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
mutex_lock(&hugetlb_fault_mutex_table[hash]);

/*
- * If folio is mapped, it was faulted in after being
- * unmapped in caller. Unmap (again) now after taking
- * the fault mutex. The mutex will prevent faults
- * until we finish removing the folio.
- *
- * This race can only happen in the hole punch case.
- * Getting here in a truncate operation is a bug.
+ * Remove folio that was part of folio_batch.
*/
- if (unlikely(folio_mapped(folio))) {
- BUG_ON(truncate_op);
-
- 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);
- }
-
- folio_lock(folio);
- /*
- * We must free the huge page and remove from page
- * cache BEFORE removing the region/reserve map
- * (hugetlb_unreserve_pages). In rare out of memory
- * conditions, removal of the region/reserve map could
- * fail. Correspondingly, the subpool and global
- * reserve usage count can need to be adjusted.
- */
- VM_BUG_ON(HPageRestoreReserve(&folio->page));
- hugetlb_delete_from_page_cache(&folio->page);
- freed++;
- if (!truncate_op) {
- if (unlikely(hugetlb_unreserve_pages(inode,
- index, index + 1, 1)))
- hugetlb_fix_reserve_counts(inode);
- }
-
- folio_unlock(folio);
+ if (remove_inode_single_folio(h, inode, mapping, folio,
+ index, truncate_op))
+ freed++;
+
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
}
folio_batch_release(&fbatch);
--
2.37.2