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

Miaohe Lin
2022-09-24T12:37:27Z

On 2022/9/15 6:18, Mike Kravetz wrote:
> 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>

LGTM with one nit below.

Reviewed-by: Miaohe Lin <linmiaohe@huawei.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.

Is this needed? remove_inode_single_folio() is called with hugetlb fault mutex held so it can't
race with page fault code?

Thanks,
Miaohe Lin