[PATCH v1 7/8] fuse: use iomap for writeback

[Joanne Koong <joannelkoong@gmail.com>]

Use iomap for dirty folio writeback in ->writepages().
This allows for granular dirty writeback of large folios.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/fuse/file.c | 114 ++++++++++++++++++++++++++++---------------------
 1 file changed, 66 insertions(+), 48 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index a0118b501880..31842ee1ce0e 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1835,7 +1835,7 @@ static void fuse_writepage_finish(struct fuse_writepage_args *wpa)
 		 * scope of the fi->lock alleviates xarray lock
 		 * contention and noticeably improves performance.
 		 */
-		folio_end_writeback(ap->folios[i]);
+		iomap_finish_folio_write(inode, ap->folios[i], 1);
 		dec_wb_stat(&bdi->wb, WB_WRITEBACK);
 		wb_writeout_inc(&bdi->wb);
 	}
@@ -2022,19 +2022,20 @@ static void fuse_writepage_add_to_bucket(struct fuse_conn *fc,
 }
 
 static void fuse_writepage_args_page_fill(struct fuse_writepage_args *wpa, struct folio *folio,
-					  uint32_t folio_index)
+					  uint32_t folio_index, loff_t offset, unsigned len)
 {
 	struct inode *inode = folio->mapping->host;
 	struct fuse_args_pages *ap = &wpa->ia.ap;
 
 	ap->folios[folio_index] = folio;
-	ap->descs[folio_index].offset = 0;
-	ap->descs[folio_index].length = folio_size(folio);
+	ap->descs[folio_index].offset = offset;
+	ap->descs[folio_index].length = len;
 
 	inc_wb_stat(&inode_to_bdi(inode)->wb, WB_WRITEBACK);
 }
 
 static struct fuse_writepage_args *fuse_writepage_args_setup(struct folio *folio,
+							     size_t offset,
 							     struct fuse_file *ff)
 {
 	struct inode *inode = folio->mapping->host;
@@ -2047,7 +2048,7 @@ static struct fuse_writepage_args *fuse_writepage_args_setup(struct folio *folio
 		return NULL;
 
 	fuse_writepage_add_to_bucket(fc, wpa);
-	fuse_write_args_fill(&wpa->ia, ff, folio_pos(folio), 0);
+	fuse_write_args_fill(&wpa->ia, ff, folio_pos(folio) + offset, 0);
 	wpa->ia.write.in.write_flags |= FUSE_WRITE_CACHE;
 	wpa->inode = inode;
 	wpa->ia.ff = ff;
@@ -2103,7 +2104,7 @@ struct fuse_fill_wb_data {
 	struct fuse_file *ff;
 	struct inode *inode;
 	unsigned int max_folios;
-	unsigned int nr_pages;
+	unsigned int nr_bytes;
 };
 
 static bool fuse_pages_realloc(struct fuse_fill_wb_data *data)
@@ -2145,21 +2146,28 @@ static void fuse_writepages_send(struct fuse_fill_wb_data *data)
 }
 
 static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio,
+				     loff_t offset, unsigned len,
 				     struct fuse_args_pages *ap,
 				     struct fuse_fill_wb_data *data)
 {
+	struct folio *prev_folio;
+	struct fuse_folio_desc prev_desc;
+
 	WARN_ON(!ap->num_folios);
 
 	/* Reached max pages */
-	if (data->nr_pages + folio_nr_pages(folio) > fc->max_pages)
+	if ((data->nr_bytes + len) / PAGE_SIZE > fc->max_pages)
 		return true;
 
 	/* Reached max write bytes */
-	if ((data->nr_pages * PAGE_SIZE) + folio_size(folio) > fc->max_write)
+	if (data->nr_bytes + len > fc->max_write)
 		return true;
 
 	/* Discontinuity */
-	if (folio_next_index(ap->folios[ap->num_folios - 1]) != folio_index(folio))
+	prev_folio = ap->folios[ap->num_folios - 1];
+	prev_desc = ap->descs[ap->num_folios - 1];
+	if ((folio_pos(prev_folio) + prev_desc.offset + prev_desc.length) !=
+	    folio_pos(folio) + offset)
 		return true;
 
 	/* Need to grow the pages array?  If so, did the expansion fail? */
@@ -2169,85 +2177,95 @@ static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio,
 	return false;
 }
 
-static int fuse_writepages_fill(struct folio *folio,
-		struct writeback_control *wbc, void *_data)
+static int fuse_iomap_writeback_folio(struct iomap_writepage_ctx *wpc,
+				      struct folio *folio, struct inode *inode,
+				      loff_t offset, unsigned len)
 {
-	struct fuse_fill_wb_data *data = _data;
+	struct fuse_fill_wb_data *data = wpc->private;
 	struct fuse_writepage_args *wpa = data->wpa;
 	struct fuse_args_pages *ap = &wpa->ia.ap;
-	struct inode *inode = data->inode;
-	struct fuse_inode *fi = get_fuse_inode(inode);
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	int err;
+	struct fuse_inode *fi = get_fuse_inode(inode);
+
+	/* len will always be page aligned */
+	WARN_ON_ONCE(len & (PAGE_SIZE - 1));
 
 	if (!data->ff) {
-		err = -EIO;
 		data->ff = fuse_write_file_get(fi);
 		if (!data->ff)
-			goto out_unlock;
+			return -EIO;
 	}
 
-	if (wpa && fuse_writepage_need_send(fc, folio, ap, data)) {
+	iomap_start_folio_write(inode, folio, 1);
+
+	if (wpa && fuse_writepage_need_send(fc, folio, offset, len, ap, data)) {
 		fuse_writepages_send(data);
 		data->wpa = NULL;
-		data->nr_pages = 0;
+		data->nr_bytes = 0;
 	}
 
 	if (data->wpa == NULL) {
-		err = -ENOMEM;
-		wpa = fuse_writepage_args_setup(folio, data->ff);
+		wpa = fuse_writepage_args_setup(folio, offset, data->ff);
 		if (!wpa)
-			goto out_unlock;
+			return -ENOMEM;
 		fuse_file_get(wpa->ia.ff);
 		data->max_folios = 1;
 		ap = &wpa->ia.ap;
 	}
-	folio_start_writeback(folio);
 
-	fuse_writepage_args_page_fill(wpa, folio, ap->num_folios);
-	data->nr_pages += folio_nr_pages(folio);
+	fuse_writepage_args_page_fill(wpa, folio, ap->num_folios,
+				      offset, len);
+	data->nr_bytes += len;
 
-	err = 0;
 	ap->num_folios++;
 	if (!data->wpa)
 		data->wpa = wpa;
-out_unlock:
-	folio_unlock(folio);
 
-	return err;
+	return 0;
+}
+
+static int fuse_iomap_submit_ioend(struct iomap_writepage_ctx *wpc, int error)
+{
+	struct fuse_fill_wb_data *data = wpc->private;
+	WARN_ON_ONCE(!data);
+
+	if (data->wpa) {
+		WARN_ON(!data->wpa->ia.ap.num_folios);
+		fuse_writepages_send(data);
+	}
+
+	if (data->ff)
+		fuse_file_put(data->ff, false);
+
+	return error;
 }
 
+static const struct iomap_writeback_ops fuse_writeback_ops = {
+	.writeback_folio	= fuse_iomap_writeback_folio,
+	.submit_ioend		= fuse_iomap_submit_ioend,
+};
+
 static int fuse_writepages(struct address_space *mapping,
 			   struct writeback_control *wbc)
 {
 	struct inode *inode = mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	struct fuse_fill_wb_data data;
-	int err;
+	struct fuse_fill_wb_data data = {
+		.inode = inode,
+	};
+	struct iomap_writepage_ctx wpc = {
+		.iomap.type = IOMAP_IN_MEM,
+		.private = &data,
+	};
 
-	err = -EIO;
 	if (fuse_is_bad(inode))
-		goto out;
+		return -EIO;
 
 	if (wbc->sync_mode == WB_SYNC_NONE &&
 	    fc->num_background >= fc->congestion_threshold)
 		return 0;
 
-	data.inode = inode;
-	data.wpa = NULL;
-	data.ff = NULL;
-	data.nr_pages = 0;
-
-	err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data);
-	if (data.wpa) {
-		WARN_ON(!data.wpa->ia.ap.num_folios);
-		fuse_writepages_send(&data);
-	}
-	if (data.ff)
-		fuse_file_put(data.ff, false);
-
-out:
-	return err;
+	return iomap_writepages(mapping, wbc, &wpc, &fuse_writeback_ops);
 }
 
 static int fuse_launder_folio(struct folio *folio)
-- 
2.47.1