Re: [PATCH 06/15] ubifs: Convert ubifs_vm_page_mkwrite() to use a folio

Zhihao Cheng
2024-01-22T11:38:17Z

在 2024/1/21 7:08, Matthew Wilcox (Oracle) 写道:
> Replace six implicit calls to compound_head() with one.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> Documentation/mm/page_cache.rst | 10 +++++++++
> fs/ubifs/file.c | 36 ++++++++++++++++-----------------
> 2 files changed, 28 insertions(+), 18 deletions(-)

Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>

>
> diff --git a/Documentation/mm/page_cache.rst b/Documentation/mm/page_cache.rst
> index 75eba7c431b2..138d61f869df 100644
> --- a/Documentation/mm/page_cache.rst
> +++ b/Documentation/mm/page_cache.rst
> @@ -3,3 +3,13 @@
> ==========
> Page Cache
> ==========
> +
> +The page cache is the primary way that the user and the rest of the kernel
> +interact with filesystems. It can be bypassed (e.g. with O_DIRECT),
> +but normal reads, writes and mmaps go through the page cache.
> +
> +Folios
> +======
> +
> +The folio is the unit of memory management within the page cache.
> +Operations
> diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
> index e755d0a11146..9dfedd91b576 100644
> --- a/fs/ubifs/file.c
> +++ b/fs/ubifs/file.c
> @@ -1519,14 +1519,14 @@ static bool ubifs_release_folio(struct folio *folio, gfp_t unused_gfp_flags)
> */
> static vm_fault_t ubifs_vm_page_mkwrite(struct vm_fault *vmf)
> {
> - struct page *page = vmf->page;
> + struct folio *folio = page_folio(vmf->page);
> struct inode *inode = file_inode(vmf->vma->vm_file);
> struct ubifs_info *c = inode->i_sb->s_fs_info;
> struct timespec64 now = current_time(inode);
> struct ubifs_budget_req req = { .new_page = 1 };
> int err, update_time;
>
> - dbg_gen("ino %lu, pg %lu, i_size %lld", inode->i_ino, page->index,
> + dbg_gen("ino %lu, pg %lu, i_size %lld", inode->i_ino, folio->index,
> i_size_read(inode));
> ubifs_assert(c, !c->ro_media && !c->ro_mount);
>
> @@ -1534,17 +1534,17 @@ static vm_fault_t ubifs_vm_page_mkwrite(struct vm_fault *vmf)
> return VM_FAULT_SIGBUS; /* -EROFS */
>
> /*
> - * We have not locked @page so far so we may budget for changing the
> - * page. Note, we cannot do this after we locked the page, because
> + * We have not locked @folio so far so we may budget for changing the
> + * folio. Note, we cannot do this after we locked the folio, because
> * budgeting may cause write-back which would cause deadlock.
> *
> - * At the moment we do not know whether the page is dirty or not, so we
> - * assume that it is not and budget for a new page. We could look at
> + * At the moment we do not know whether the folio is dirty or not, so we
> + * assume that it is not and budget for a new folio. We could look at
> * the @PG_private flag and figure this out, but we may race with write
> - * back and the page state may change by the time we lock it, so this
> + * back and the folio state may change by the time we lock it, so this
> * would need additional care. We do not bother with this at the
> * moment, although it might be good idea to do. Instead, we allocate
> - * budget for a new page and amend it later on if the page was in fact
> + * budget for a new folio and amend it later on if the folio was in fact
> * dirty.
> *
> * The budgeting-related logic of this function is similar to what we
> @@ -1567,21 +1567,21 @@ static vm_fault_t ubifs_vm_page_mkwrite(struct vm_fault *vmf)
> return VM_FAULT_SIGBUS;
> }
>
> - lock_page(page);
> - if (unlikely(page->mapping != inode->i_mapping ||
> - page_offset(page) > i_size_read(inode))) {
> - /* Page got truncated out from underneath us */
> + folio_lock(folio);
> + if (unlikely(folio->mapping != inode->i_mapping ||
> + folio_pos(folio) >= i_size_read(inode))) {
> + /* Folio got truncated out from underneath us */
> goto sigbus;
> }
>
> - if (PagePrivate(page))
> + if (folio->private)
> release_new_page_budget(c);
> else {
> - if (!PageChecked(page))
> + if (!folio_test_checked(folio))
> ubifs_convert_page_budget(c);
> - attach_page_private(page, (void *)1);
> + folio_attach_private(folio, (void *)1);
> atomic_long_inc(&c->dirty_pg_cnt);
> - __set_page_dirty_nobuffers(page);
> + filemap_dirty_folio(folio->mapping, folio);
> }
>
> if (update_time) {
> @@ -1597,11 +1597,11 @@ static vm_fault_t ubifs_vm_page_mkwrite(struct vm_fault *vmf)
> ubifs_release_dirty_inode_budget(c, ui);
> }
>
> - wait_for_stable_page(page);
> + folio_wait_stable(folio);
> return VM_FAULT_LOCKED;
>
> sigbus:
> - unlock_page(page);
> + folio_unlock(folio);
> ubifs_release_budget(c, &req);
> return VM_FAULT_SIGBUS;
> }