From 68d32527d340b0d13c8cf6495d6ab4332adca09a Mon Sep 17 00:00:00 2001 From: Mike Kravetz Date: Mon, 13 Jun 2022 13:36:48 -0700 Subject: [PATCH] hugetlbfs: zero partial pages during fallocate hole punch hugetlbfs fallocate support was originally added with commit 70c3547e36f5 ("hugetlbfs: add hugetlbfs_fallocate()"). Initial support only operated on whole hugetlb pages. This makes sense for populating files as other interfaces such as mmap and truncate require hugetlb page size alignment. Only operating on whole hugetlb pages for the hole punch case was a simplification and there was no compelling use case to zero partial pages. In a recent discussion[1] it was assumed that hugetlbfs hole punch would zero partial hugetlb pages as that is in line with the man page description saying 'partial filesystem blocks are zeroed'. However, the hugetlbfs hole punch code actually does this: hole_start = round_up(offset, hpage_size); hole_end = round_down(offset + len, hpage_size); Modify code to zero partial hugetlb pages in hole punch range. It is possible that application code could note a change in behavior. However, that would imply the code is passing in an unaligned range and expecting only whole pages be removed. This is unlikely as the fallocate documentation states the opposite. The current hugetlbfs fallocate hole punch behavior is tested with the libhugetlbfs test fallocate_align[2]. This test will be updated to validate partial page zeroing. [1] https://lore.kernel.org/linux-mm/20571829-9d3d-0b48-817c-b6b15565f651@redhat.com/ [2] https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/fallocate_align.c Link: https://lkml.kernel.org/r/YqeiMlZDKI1Kabfe@monkey Signed-off-by: Mike Kravetz Reviewed-by: Muchun Song Cc: David Hildenbrand Cc: Naoya Horiguchi Cc: Axel Rasmussen Cc: Dave Hansen Cc: Michal Hocko Cc: Matthew Wilcox Signed-off-by: Andrew Morton --- fs/hugetlbfs/inode.c | 72 +++++++++++++++++++++++++++++++++----------- 1 file changed, 55 insertions(+), 17 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 62408047e8d7..02eb72351b15 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -600,41 +600,79 @@ static void hugetlb_vmtruncate(struct inode *inode, loff_t offset) remove_inode_hugepages(inode, offset, LLONG_MAX); } +static void hugetlbfs_zero_partial_page(struct hstate *h, + struct address_space *mapping, + loff_t start, + loff_t end) +{ + pgoff_t idx = start >> huge_page_shift(h); + struct folio *folio; + + folio = filemap_lock_folio(mapping, idx); + if (!folio) + return; + + start = start & ~huge_page_mask(h); + end = end & ~huge_page_mask(h); + if (!end) + end = huge_page_size(h); + + folio_zero_segment(folio, (size_t)start, (size_t)end); + + folio_unlock(folio); + folio_put(folio); +} + static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len) { + struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode); + struct address_space *mapping = inode->i_mapping; struct hstate *h = hstate_inode(inode); loff_t hpage_size = huge_page_size(h); loff_t hole_start, hole_end; /* - * For hole punch round up the beginning offset of the hole and - * round down the end. + * hole_start and hole_end indicate the full pages within the hole. */ hole_start = round_up(offset, hpage_size); hole_end = round_down(offset + len, hpage_size); + inode_lock(inode); + + /* protected by i_rwsem */ + if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) { + inode_unlock(inode); + return -EPERM; + } + + i_mmap_lock_write(mapping); + + /* If range starts before first full page, zero partial page. */ + if (offset < hole_start) + hugetlbfs_zero_partial_page(h, mapping, + offset, min(offset + len, hole_start)); + + /* Unmap users of full pages in the hole. */ if (hole_end > hole_start) { - struct address_space *mapping = inode->i_mapping; - struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode); - - inode_lock(inode); - - /* protected by i_rwsem */ - if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) { - inode_unlock(inode); - return -EPERM; - } - - i_mmap_lock_write(mapping); if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)) hugetlb_vmdelete_list(&mapping->i_mmap, hole_start >> PAGE_SHIFT, hole_end >> PAGE_SHIFT, 0); - i_mmap_unlock_write(mapping); - remove_inode_hugepages(inode, hole_start, hole_end); - inode_unlock(inode); } + /* If range extends beyond last full page, zero partial page. */ + if ((offset + len) > hole_end && (offset + len) > hole_start) + hugetlbfs_zero_partial_page(h, mapping, + hole_end, offset + len); + + i_mmap_unlock_write(mapping); + + /* Remove full pages from the file. */ + if (hole_end > hole_start) + remove_inode_hugepages(inode, hole_start, hole_end); + + inode_unlock(inode); + return 0; }