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Commit 48f170fb authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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tmpfs: simplify unuse and writepage 



shmem_unuse_inode() and shmem_writepage() contain a little code to cope
with pages inserted independently into the filecache, probably by a
filesystem stacked on top of tmpfs, then fed to its ->readpage() or
->writepage().

Unionfs was indeed experimenting with working in that way three years ago,
but I find no current examples: nowadays the stacking filesystems use vfs
interfaces to the lower filesystem.

It's now illegal: remove most of that code, adding some WARN_ON_ONCEs.

Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: Erez Zadok <ezk@fsl.cs.sunysb.edu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 27ab7006

mm/shmem.c

+16 −34
Original line number Diff line number Diff line
@@ -972,20 +972,7 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s 
	error = add_to_page_cache_locked(page, mapping, idx, GFP_NOWAIT);

	/* which does mem_cgroup_uncharge_cache_page on error */



	if (error == -EEXIST) {

		struct page *filepage = find_get_page(mapping, idx);

		error = 1;

		if (filepage) {

			/*

			 * There might be a more uptodate page coming down

			 * from a stacked writepage: forget our swappage if so.

			 */

			if (PageUptodate(filepage))

				error = 0;

			page_cache_release(filepage);

		}

	}

	if (!error) {

	if (error != -ENOMEM) {

		delete_from_swap_cache(page);

		set_page_dirty(page);

		info->flags |= SHMEM_PAGEIN;
@@ -1072,16 +1059,17 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) 
	/*

	 * shmem_backing_dev_info's capabilities prevent regular writeback or

	 * sync from ever calling shmem_writepage; but a stacking filesystem

	 * may use the ->writepage of its underlying filesystem, in which case

	 * might use ->writepage of its underlying filesystem, in which case

	 * tmpfs should write out to swap only in response to memory pressure,

	 * and not for the writeback threads or sync.  However, in those cases,

	 * we do still want to check if there's a redundant swappage to be

	 * discarded.

	 * and not for the writeback threads or sync.

	 */

	if (wbc->for_reclaim)

	if (!wbc->for_reclaim) {

		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */

		goto redirty;

	}

	swap = get_swap_page();

	else

		swap.val = 0;

	if (!swap.val)

		goto redirty;



	/*

	 * Add inode to shmem_unuse()'s list of swapped-out inodes,
@@ -1092,14 +1080,11 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) 
	 * we've taken the spinlock, because shmem_unuse_inode() will

	 * prune a !swapped inode from the swaplist under both locks.

	 */

	if (swap.val) {

	mutex_lock(&shmem_swaplist_mutex);

	if (list_empty(&info->swaplist))

		list_add_tail(&info->swaplist, &shmem_swaplist);

	}



	spin_lock(&info->lock);

	if (swap.val)

	mutex_unlock(&shmem_swaplist_mutex);



	if (index >= info->next_index) {
@@ -1108,16 +1093,13 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) 
	}

	entry = shmem_swp_entry(info, index, NULL);

	if (entry->val) {

		/*

		 * The more uptodate page coming down from a stacked

		 * writepage should replace our old swappage.

		 */

		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */

		free_swap_and_cache(*entry);

		shmem_swp_set(info, entry, 0);

	}

	shmem_recalc_inode(inode);



	if (swap.val && add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {

	if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {

		delete_from_page_cache(page);

		shmem_swp_set(info, entry, swap.val);

		shmem_swp_unmap(entry);