vfs-6.19-rc1.writeback

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Merge tag 'vfs-6.19-rc1.writeback' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull writeback updates from Christian Brauner:
 "Features:

   - Allow file systems to increase the minimum writeback chunk size.

     The relatively low minimal writeback size of 4MiB means that
     written back inodes on rotational media are switched a lot. Besides
     introducing additional seeks, this also can lead to extreme file
     fragmentation on zoned devices when a lot of files are cached
     relative to the available writeback bandwidth.

     This adds a superblock field that allows the file system to
     override the default size, and sets it to the zone size for zoned
     XFS.

   - Add logging for slow writeback when it exceeds
     sysctl_hung_task_timeout_secs. This helps identify tasks waiting
     for a long time and pinpoint potential issues. Recording the
     starting jiffies is also useful when debugging a crashed vmcore.

   - Wake up waiting tasks when finishing the writeback of a chunk

  Cleanups:

   - filemap_* writeback interface cleanups.

     Adding filemap_fdatawrite_wbc ended up being a mistake, as all but
     the original btrfs caller should be using better high level
     interfaces instead.

     This series removes all these low-level interfaces, switches btrfs
     to a more specific interface, and cleans up other too low-level
     interfaces. With this the writeback_control that is passed to the
     writeback code is only initialized in three places.

   - Remove __filemap_fdatawrite, __filemap_fdatawrite_range, and
     filemap_fdatawrite_wbc

   - Add filemap_flush_nr helper for btrfs

   - Push struct writeback_control into start_delalloc_inodes in btrfs

   - Rename filemap_fdatawrite_range_kick to filemap_flush_range

   - Stop opencoding filemap_fdatawrite_range in 9p, ocfs2, and mm

   - Make wbc_to_tag() inline and use it in fs"

* tag 'vfs-6.19-rc1.writeback' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  fs: Make wbc_to_tag() inline and use it in fs.
  xfs: set s_min_writeback_pages for zoned file systems
  writeback: allow the file system to override MIN_WRITEBACK_PAGES
  writeback: cleanup writeback_chunk_size
  mm: rename filemap_fdatawrite_range_kick to filemap_flush_range
  mm: remove __filemap_fdatawrite_range
  mm: remove filemap_fdatawrite_wbc
  mm: remove __filemap_fdatawrite
  mm,btrfs: add a filemap_flush_nr helper
  btrfs: push struct writeback_control into start_delalloc_inodes
  btrfs: use the local tmp_inode variable in start_delalloc_inodes
  ocfs2: don't opencode filemap_fdatawrite_range in ocfs2_journal_submit_inode_data_buffers
  9p: don't opencode filemap_fdatawrite_range in v9fs_mmap_vm_close
  mm: don't opencode filemap_fdatawrite_range in filemap_invalidate_inode
  writeback: Add logging for slow writeback (exceeds sysctl_hung_task_timeout_secs)
  writeback: Wake up waiting tasks when finishing the writeback of a chunk.

fs/9p/vfs_file.c

@@ -483,24 +483,15 @@ v9fs_vm_page_mkwrite(struct vm_fault *vmf)
 
 static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
 {
-	struct inode *inode;
-
-	struct writeback_control wbc = {
-		.nr_to_write = LONG_MAX,
-		.sync_mode = WB_SYNC_ALL,
-		.range_start = (loff_t)vma->vm_pgoff * PAGE_SIZE,
-		 /* absolute end, byte at end included */
-		.range_end = (loff_t)vma->vm_pgoff * PAGE_SIZE +
-			(vma->vm_end - vma->vm_start - 1),
-	};
-
 	if (!(vma->vm_flags & VM_SHARED))
 		return;
 
 	p9_debug(P9_DEBUG_VFS, "9p VMA close, %p, flushing", vma);
 
-	inode = file_inode(vma->vm_file);
+	filemap_fdatawrite_range(file_inode(vma->vm_file)->i_mapping,
-	filemap_fdatawrite_wbc(inode->i_mapping, &wbc);
+			(loff_t)vma->vm_pgoff * PAGE_SIZE,
+			(loff_t)vma->vm_pgoff * PAGE_SIZE +
+				(vma->vm_end - vma->vm_start - 1));
 }
 
 static const struct vm_operations_struct v9fs_mmap_file_vm_ops = {

fs/btrfs/extent_io.c

@@ -2468,10 +2468,7 @@ static int extent_write_cache_pages(struct address_space *mapping,
 			       &BTRFS_I(inode)->runtime_flags))
 		wbc->tagged_writepages = 1;
 
-	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+	tag = wbc_to_tag(wbc);
-		tag = PAGECACHE_TAG_TOWRITE;
-	else
-		tag = PAGECACHE_TAG_DIRTY;
 retry:
 	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
 		tag_pages_for_writeback(mapping, index, end);

fs/btrfs/inode.c

@@ -8715,15 +8715,13 @@ static struct btrfs_delalloc_work *btrfs_alloc_delalloc_work(struct inode *inode
  * some fairly slow code that needs optimization. This walks the list
  * of all the inodes with pending delalloc and forces them to disk.
  */
-static int start_delalloc_inodes(struct btrfs_root *root,
+static int start_delalloc_inodes(struct btrfs_root *root, long *nr_to_write,
-				 struct writeback_control *wbc, bool snapshot,
+				 bool snapshot, bool in_reclaim_context)
-				 bool in_reclaim_context)
 {
 	struct btrfs_delalloc_work *work, *next;
 	LIST_HEAD(works);
 	LIST_HEAD(splice);
 	int ret = 0;
-	bool full_flush = wbc->nr_to_write == LONG_MAX;
 
 	mutex_lock(&root->delalloc_mutex);
 	spin_lock(&root->delalloc_lock);
@@ -8749,10 +8747,10 @@ static int start_delalloc_inodes(struct btrfs_root *root,
 
 		if (snapshot)
 			set_bit(BTRFS_INODE_SNAPSHOT_FLUSH, &inode->runtime_flags);
-		if (full_flush) {
+		if (nr_to_write == NULL) {
-			work = btrfs_alloc_delalloc_work(&inode->vfs_inode);
+			work = btrfs_alloc_delalloc_work(tmp_inode);
 			if (!work) {
-				iput(&inode->vfs_inode);
+				iput(tmp_inode);
 				ret = -ENOMEM;
 				goto out;
 			}
@@ -8760,9 +8758,11 @@ static int start_delalloc_inodes(struct btrfs_root *root,
 			btrfs_queue_work(root->fs_info->flush_workers,
 					 &work->work);
 		} else {
-			ret = filemap_fdatawrite_wbc(inode->vfs_inode.i_mapping, wbc);
+			ret = filemap_flush_nr(tmp_inode->i_mapping,
+					nr_to_write);
 			btrfs_add_delayed_iput(inode);
-			if (ret || wbc->nr_to_write <= 0)
+
+			if (ret || *nr_to_write <= 0)
 				goto out;
 		}
 		cond_resched();
@@ -8788,29 +8788,17 @@ static int start_delalloc_inodes(struct btrfs_root *root,
 
 int btrfs_start_delalloc_snapshot(struct btrfs_root *root, bool in_reclaim_context)
 {
-	struct writeback_control wbc = {
-		.nr_to_write = LONG_MAX,
-		.sync_mode = WB_SYNC_NONE,
-		.range_start = 0,
-		.range_end = LLONG_MAX,
-	};
 	struct btrfs_fs_info *fs_info = root->fs_info;
 
 	if (BTRFS_FS_ERROR(fs_info))
 		return -EROFS;
-
+	return start_delalloc_inodes(root, NULL, true, in_reclaim_context);
-	return start_delalloc_inodes(root, &wbc, true, in_reclaim_context);
 }
 
 int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, long nr,
 			       bool in_reclaim_context)
 {
-	struct writeback_control wbc = {
+	long *nr_to_write = nr == LONG_MAX ? NULL : &nr;
-		.nr_to_write = nr,
-		.sync_mode = WB_SYNC_NONE,
-		.range_start = 0,
-		.range_end = LLONG_MAX,
-	};
 	struct btrfs_root *root;
 	LIST_HEAD(splice);
 	int ret;
@@ -8822,13 +8810,6 @@ int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, long nr,
 	spin_lock(&fs_info->delalloc_root_lock);
 	list_splice_init(&fs_info->delalloc_roots, &splice);
 	while (!list_empty(&splice)) {
-		/*
-		 * Reset nr_to_write here so we know that we're doing a full
-		 * flush.
-		 */
-		if (nr == LONG_MAX)
-			wbc.nr_to_write = LONG_MAX;
-
 		root = list_first_entry(&splice, struct btrfs_root,
 					delalloc_root);
 		root = btrfs_grab_root(root);
@@ -8837,9 +8818,10 @@ int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, long nr,
 			       &fs_info->delalloc_roots);
 		spin_unlock(&fs_info->delalloc_root_lock);
 
-		ret = start_delalloc_inodes(root, &wbc, false, in_reclaim_context);
+		ret = start_delalloc_inodes(root, nr_to_write, false,
+				in_reclaim_context);
 		btrfs_put_root(root);
-		if (ret < 0 || wbc.nr_to_write <= 0)
+		if (ret < 0 || nr <= 0)
 			goto out;
 		spin_lock(&fs_info->delalloc_root_lock);
 	}

fs/ceph/addr.c

@@ -1045,11 +1045,7 @@ void ceph_init_writeback_ctl(struct address_space *mapping,
 	ceph_wbc->index = ceph_wbc->start_index;
 	ceph_wbc->end = -1;
 
-	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
+	ceph_wbc->tag = wbc_to_tag(wbc);
-		ceph_wbc->tag = PAGECACHE_TAG_TOWRITE;
-	} else {
-		ceph_wbc->tag = PAGECACHE_TAG_DIRTY;
-	}
 
 	ceph_wbc->op_idx = -1;
 	ceph_wbc->num_ops = 0;

fs/ext4/inode.c

@@ -2618,10 +2618,7 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 	handle_t *handle = NULL;
 	int bpp = ext4_journal_blocks_per_folio(mpd->inode);
 
-	if (mpd->wbc->sync_mode == WB_SYNC_ALL || mpd->wbc->tagged_writepages)
+	tag = wbc_to_tag(mpd->wbc);
-		tag = PAGECACHE_TAG_TOWRITE;
-	else
-		tag = PAGECACHE_TAG_DIRTY;
 
 	mpd->map.m_len = 0;
 	mpd->next_pos = mpd->start_pos;

fs/f2fs/data.c

@@ -2986,10 +2986,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
 			range_whole = 1;
 	}
-	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+	tag = wbc_to_tag(wbc);
-		tag = PAGECACHE_TAG_TOWRITE;
-	else
-		tag = PAGECACHE_TAG_DIRTY;
 retry:
 	retry = 0;
 	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)

fs/fs-writeback.c

@@ -14,6 +14,7 @@
  *		Additions for address_space-based writeback
  */
 
+#include <linux/sched/sysctl.h>
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/spinlock.h>
@@ -31,11 +32,6 @@
 #include <linux/memcontrol.h>
 #include "internal.h"
 
-/*
- * 4MB minimal write chunk size
- */
-#define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_SHIFT - 10))
-
 /*
  * Passed into wb_writeback(), essentially a subset of writeback_control
  */
@@ -200,6 +196,19 @@ static void wb_queue_work(struct bdi_writeback *wb,
 	spin_unlock_irq(&wb->work_lock);
 }
 
+static bool wb_wait_for_completion_cb(struct wb_completion *done)
+{
+	unsigned long waited_secs = (jiffies - done->wait_start) / HZ;
+
+	done->progress_stamp = jiffies;
+	if (waited_secs > sysctl_hung_task_timeout_secs)
+		pr_info("INFO: The task %s:%d has been waiting for writeback "
+			"completion for more than %lu seconds.",
+			current->comm, current->pid, waited_secs);
+
+	return !atomic_read(&done->cnt);
+}
+
 /**
  * wb_wait_for_completion - wait for completion of bdi_writeback_works
  * @done: target wb_completion
@@ -212,8 +221,9 @@ static void wb_queue_work(struct bdi_writeback *wb,
  */
 void wb_wait_for_completion(struct wb_completion *done)
 {
+	done->wait_start = jiffies;
 	atomic_dec(&done->cnt);		/* put down the initial count */
-	wait_event(*done->waitq, !atomic_read(&done->cnt));
+	wait_event(*done->waitq, wb_wait_for_completion_cb(done));
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK
@@ -808,9 +818,9 @@ static void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
  * @wbc: writeback_control of interest
  * @inode: target inode
  *
- * This function is to be used by __filemap_fdatawrite_range(), which is an
+ * This function is to be used by filemap_writeback(), which is an alternative
- * alternative entry point into writeback code, and first ensures @inode is
+ * entry point into writeback code, and first ensures @inode is associated with
- * associated with a bdi_writeback and attaches it to @wbc.
+ * a bdi_writeback and attaches it to @wbc.
  */
 void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
 		struct inode *inode)
@@ -1882,8 +1892,8 @@ static int writeback_single_inode(struct inode *inode,
 	return ret;
 }
 
-static long writeback_chunk_size(struct bdi_writeback *wb,
+static long writeback_chunk_size(struct super_block *sb,
-				 struct wb_writeback_work *work)
+		struct bdi_writeback *wb, struct wb_writeback_work *work)
 {
 	long pages;
 
@@ -1901,16 +1911,13 @@ static long writeback_chunk_size(struct bdi_writeback *wb,
 	 *                   (maybe slowly) sync all tagged pages
 	 */
 	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
-		pages = LONG_MAX;
+		return LONG_MAX;
-	else {
+
 	pages = min(wb->avg_write_bandwidth / 2,
 		    global_wb_domain.dirty_limit / DIRTY_SCOPE);
 	pages = min(pages, work->nr_pages);
-		pages = round_down(pages + MIN_WRITEBACK_PAGES,
+	return round_down(pages + sb->s_min_writeback_pages,
-				   MIN_WRITEBACK_PAGES);
+			sb->s_min_writeback_pages);
-	}
-
-	return pages;
 }
 
 /*
@@ -2012,7 +2019,7 @@ static long writeback_sb_inodes(struct super_block *sb,
 		inode_state_set(inode, I_SYNC);
 		wbc_attach_and_unlock_inode(&wbc, inode);
 
-		write_chunk = writeback_chunk_size(wb, work);
+		write_chunk = writeback_chunk_size(inode->i_sb, wb, work);
 		wbc.nr_to_write = write_chunk;
 		wbc.pages_skipped = 0;
 
@@ -2022,6 +2029,12 @@ static long writeback_sb_inodes(struct super_block *sb,
 		 */
 		__writeback_single_inode(inode, &wbc);
 
+		/* Report progress to inform the hung task detector of the progress. */
+		if (work->done && work->done->progress_stamp &&
+		   (jiffies - work->done->progress_stamp) > HZ *
+		   sysctl_hung_task_timeout_secs / 2)
+			wake_up_all(work->done->waitq);
+
 		wbc_detach_inode(&wbc);
 		work->nr_pages -= write_chunk - wbc.nr_to_write;
 		wrote = write_chunk - wbc.nr_to_write - wbc.pages_skipped;

fs/gfs2/aops.c

@@ -311,10 +311,7 @@ static int gfs2_write_cache_jdata(struct address_space *mapping,
 			range_whole = 1;
 		cycled = 1; /* ignore range_cyclic tests */
 	}
-	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+	tag = wbc_to_tag(wbc);
-		tag = PAGECACHE_TAG_TOWRITE;
-	else
-		tag = PAGECACHE_TAG_DIRTY;
 
 retry:
 	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)

fs/ocfs2/journal.c

@@ -902,15 +902,8 @@ int ocfs2_journal_alloc(struct ocfs2_super *osb)
 
 static int ocfs2_journal_submit_inode_data_buffers(struct jbd2_inode *jinode)
 {
-	struct address_space *mapping = jinode->i_vfs_inode->i_mapping;
+	return filemap_fdatawrite_range(jinode->i_vfs_inode->i_mapping,
-	struct writeback_control wbc = {
+			jinode->i_dirty_start, jinode->i_dirty_end);
-		.sync_mode =  WB_SYNC_ALL,
-		.nr_to_write = mapping->nrpages * 2,
-		.range_start = jinode->i_dirty_start,
-		.range_end = jinode->i_dirty_end,
-	};
-
-	return filemap_fdatawrite_wbc(mapping, &wbc);
 }
 
 int ocfs2_journal_init(struct ocfs2_super *osb, int *dirty)

fs/super.c

@@ -389,6 +389,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 		goto fail;
 	if (list_lru_init_memcg(&s->s_inode_lru, s->s_shrink))
 		goto fail;
+	s->s_min_writeback_pages = MIN_WRITEBACK_PAGES;
 	return s;
 
 fail:

fs/sync.c

@@ -281,14 +281,12 @@ int sync_file_range(struct file *file, loff_t offset, loff_t nbytes,
 	}
 
 	if (flags & SYNC_FILE_RANGE_WRITE) {
-		int sync_mode = WB_SYNC_NONE;
-
 		if ((flags & SYNC_FILE_RANGE_WRITE_AND_WAIT) ==
 			     SYNC_FILE_RANGE_WRITE_AND_WAIT)
-			sync_mode = WB_SYNC_ALL;
+			ret = filemap_fdatawrite_range(mapping, offset,
-
+					endbyte);
-		ret = __filemap_fdatawrite_range(mapping, offset, endbyte,
+		else
-						 sync_mode);
+			ret = filemap_flush_range(mapping, offset, endbyte);
 		if (ret < 0)
 			goto out;
 	}

fs/xfs/xfs_zone_alloc.c

@@ -1204,6 +1204,7 @@ xfs_mount_zones(
 		.mp		= mp,
 	};
 	struct xfs_buftarg	*bt = mp->m_rtdev_targp;
+	xfs_extlen_t		zone_blocks = mp->m_groups[XG_TYPE_RTG].blocks;
 	int			error;
 
 	if (!bt) {
@@ -1234,10 +1235,33 @@ xfs_mount_zones(
 		return -ENOMEM;
 
 	xfs_info(mp, "%u zones of %u blocks (%u max open zones)",
-		 mp->m_sb.sb_rgcount, mp->m_groups[XG_TYPE_RTG].blocks,
+		 mp->m_sb.sb_rgcount, zone_blocks, mp->m_max_open_zones);
-		 mp->m_max_open_zones);
 	trace_xfs_zones_mount(mp);
 
+	/*
+	 * The writeback code switches between inodes regularly to provide
+	 * fairness.  The default lower bound is 4MiB, but for zoned file
+	 * systems we want to increase that both to reduce seeks, but also more
+	 * importantly so that workloads that writes files in a multiple of the
+	 * zone size do not get fragmented and require garbage collection when
+	 * they shouldn't.  Increase is to the zone size capped by the max
+	 * extent len.
+	 *
+	 * Note that because s_min_writeback_pages is a superblock field, this
+	 * value also get applied to non-zoned files on the data device if
+	 * there are any.  On typical zoned setup all data is on the RT device
+	 * because using the more efficient sequential write required zones
+	 * is the reason for using the zone allocator, and either the RT device
+	 * and the (meta)data device are on the same block device, or the
+	 * (meta)data device is on a fast SSD while the data on the RT device
+	 * is on a SMR HDD.  In any combination of the above cases enforcing
+	 * the higher min_writeback_pages for non-RT inodes is either a noop
+	 * or beneficial.
+	 */
+	mp->m_super->s_min_writeback_pages =
+		XFS_FSB_TO_B(mp, min(zone_blocks, XFS_MAX_BMBT_EXTLEN)) >>
+			PAGE_SHIFT;
+
 	if (bdev_is_zoned(bt->bt_bdev)) {
 		error = blkdev_report_zones(bt->bt_bdev,
 				XFS_FSB_TO_BB(mp, mp->m_sb.sb_rtstart),

include/linux/backing-dev-defs.h

@@ -63,6 +63,8 @@ enum wb_reason {
 struct wb_completion {
 	atomic_t		cnt;
 	wait_queue_head_t	*waitq;
+	unsigned long progress_stamp;	/* The jiffies when slow progress is detected */
+	unsigned long wait_start;	/* The jiffies when waiting for the writeback work to finish */
 };
 
 #define __WB_COMPLETION_INIT(_waitq)	\

include/linux/fs.h

@@ -1642,6 +1642,7 @@ struct super_block {
 
 	spinlock_t		s_inode_wblist_lock;
 	struct list_head	s_inodes_wb;	/* writeback inodes */
+	long			s_min_writeback_pages;
 } __randomize_layout;
 
 static inline struct user_namespace *i_user_ns(const struct inode *inode)
@@ -3075,7 +3076,7 @@ extern int __must_check file_fdatawait_range(struct file *file, loff_t lstart,
 extern int __must_check file_check_and_advance_wb_err(struct file *file);
 extern int __must_check file_write_and_wait_range(struct file *file,
 						loff_t start, loff_t end);
-int filemap_fdatawrite_range_kick(struct address_space *mapping, loff_t start,
+int filemap_flush_range(struct address_space *mapping, loff_t start,
 		loff_t end);
 
 static inline int file_write_and_wait(struct file *file)
@@ -3112,7 +3113,7 @@ static inline ssize_t generic_write_sync(struct kiocb *iocb, ssize_t count)
 	} else if (iocb->ki_flags & IOCB_DONTCACHE) {
 		struct address_space *mapping = iocb->ki_filp->f_mapping;
 
-		filemap_fdatawrite_range_kick(mapping, iocb->ki_pos - count,
+		filemap_flush_range(mapping, iocb->ki_pos - count,
 				iocb->ki_pos - 1);
 	}
 

include/linux/pagemap.h

@@ -38,6 +38,7 @@ int filemap_invalidate_pages(struct address_space *mapping,
 int write_inode_now(struct inode *, int sync);
 int filemap_fdatawrite(struct address_space *);
 int filemap_flush(struct address_space *);
+int filemap_flush_nr(struct address_space *mapping, long *nr_to_write);
 int filemap_fdatawait_keep_errors(struct address_space *mapping);
 int filemap_fdatawait_range(struct address_space *, loff_t lstart, loff_t lend);
 int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
@@ -53,14 +54,10 @@ static inline int filemap_fdatawait(struct address_space *mapping)
 bool filemap_range_has_page(struct address_space *, loff_t lstart, loff_t lend);
 int filemap_write_and_wait_range(struct address_space *mapping,
 		loff_t lstart, loff_t lend);
-int __filemap_fdatawrite_range(struct address_space *mapping,
-		loff_t start, loff_t end, int sync_mode);
 int filemap_fdatawrite_range(struct address_space *mapping,
 		loff_t start, loff_t end);
 int filemap_check_errors(struct address_space *mapping);
 void __filemap_set_wb_err(struct address_space *mapping, int err);
-int filemap_fdatawrite_wbc(struct address_space *mapping,
-			   struct writeback_control *wbc);
 int kiocb_write_and_wait(struct kiocb *iocb, size_t count);
 
 static inline int filemap_write_and_wait(struct address_space *mapping)

include/linux/writeback.h

@@ -189,6 +189,13 @@ void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
 void inode_wait_for_writeback(struct inode *inode);
 void inode_io_list_del(struct inode *inode);
 
+static inline xa_mark_t wbc_to_tag(struct writeback_control *wbc)
+{
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+		return PAGECACHE_TAG_TOWRITE;
+	return PAGECACHE_TAG_DIRTY;
+}
+
 #ifdef CONFIG_CGROUP_WRITEBACK
 
 #include <linux/cgroup.h>
@@ -367,4 +374,9 @@ bool redirty_page_for_writepage(struct writeback_control *, struct page *);
 void sb_mark_inode_writeback(struct inode *inode);
 void sb_clear_inode_writeback(struct inode *inode);
 
+/*
+ * 4MB minimal write chunk size
+ */
+#define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_SHIFT - 10))
+
 #endif		/* WRITEBACK_H */

mm/fadvise.c

@@ -111,8 +111,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		spin_unlock(&file->f_lock);
 		break;
 	case POSIX_FADV_DONTNEED:
-		__filemap_fdatawrite_range(mapping, offset, endbyte,
+		filemap_flush_range(mapping, offset, endbyte);
-					   WB_SYNC_NONE);
 
 		/*
 		 * First and last FULL page! Partial pages are deliberately

mm/filemap.c

@@ -366,83 +366,60 @@ static int filemap_check_and_keep_errors(struct address_space *mapping)
 	return 0;
 }
 
-/**
+static int filemap_writeback(struct address_space *mapping, loff_t start,
- * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range
+		loff_t end, enum writeback_sync_modes sync_mode,
- * @mapping:	address space structure to write
+		long *nr_to_write)
- * @wbc:	the writeback_control controlling the writeout
- *
- * Call writepages on the mapping using the provided wbc to control the
- * writeout.
- *
- * Return: %0 on success, negative error code otherwise.
- */
-int filemap_fdatawrite_wbc(struct address_space *mapping,
-			   struct writeback_control *wbc)
 {
+	struct writeback_control wbc = {
+		.sync_mode	= sync_mode,
+		.nr_to_write	= nr_to_write ? *nr_to_write : LONG_MAX,
+		.range_start	= start,
+		.range_end	= end,
+	};
 	int ret;
 
 	if (!mapping_can_writeback(mapping) ||
 	    !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
 		return 0;
 
-	wbc_attach_fdatawrite_inode(wbc, mapping->host);
+	wbc_attach_fdatawrite_inode(&wbc, mapping->host);
-	ret = do_writepages(mapping, wbc);
+	ret = do_writepages(mapping, &wbc);
-	wbc_detach_inode(wbc);
+	wbc_detach_inode(&wbc);
+
+	if (!ret && nr_to_write)
+		*nr_to_write = wbc.nr_to_write;
 	return ret;
 }
-EXPORT_SYMBOL(filemap_fdatawrite_wbc);
 
 /**
- * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
+ * filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:	address space structure to write
  * @start:	offset in bytes where the range starts
  * @end:	offset in bytes where the range ends (inclusive)
- * @sync_mode:	enable synchronous operation
  *
  * Start writeback against all of a mapping's dirty pages that lie
  * within the byte offsets <start, end> inclusive.
  *
- * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
+ * This is a data integrity operation that waits upon dirty or in writeback
- * opposed to a regular memory cleansing writeback.  The difference between
+ * pages.
- * these two operations is that if a dirty page/buffer is encountered, it must
- * be waited upon, and not just skipped over.
  *
  * Return: %0 on success, negative error code otherwise.
  */
-int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
-				loff_t end, int sync_mode)
-{
-	struct writeback_control wbc = {
-		.sync_mode = sync_mode,
-		.nr_to_write = LONG_MAX,
-		.range_start = start,
-		.range_end = end,
-	};
-
-	return filemap_fdatawrite_wbc(mapping, &wbc);
-}
-
-static inline int __filemap_fdatawrite(struct address_space *mapping,
-	int sync_mode)
-{
-	return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
-}
-
-int filemap_fdatawrite(struct address_space *mapping)
-{
-	return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
-}
-EXPORT_SYMBOL(filemap_fdatawrite);
-
 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
 		loff_t end)
 {
-	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
+	return filemap_writeback(mapping, start, end, WB_SYNC_ALL, NULL);
 }
 EXPORT_SYMBOL(filemap_fdatawrite_range);
 
+int filemap_fdatawrite(struct address_space *mapping)
+{
+	return filemap_fdatawrite_range(mapping, 0, LLONG_MAX);
+}
+EXPORT_SYMBOL(filemap_fdatawrite);
+
 /**
- * filemap_fdatawrite_range_kick - start writeback on a range
+ * filemap_flush_range - start writeback on a range
  * @mapping:	target address_space
  * @start:	index to start writeback on
  * @end:	last (inclusive) index for writeback
@@ -452,12 +429,12 @@ EXPORT_SYMBOL(filemap_fdatawrite_range);
  *
  * Return: %0 on success, negative error code otherwise.
  */
-int filemap_fdatawrite_range_kick(struct address_space *mapping, loff_t start,
+int filemap_flush_range(struct address_space *mapping, loff_t start,
 				  loff_t end)
 {
-	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_NONE);
+	return filemap_writeback(mapping, start, end, WB_SYNC_NONE, NULL);
 }
-EXPORT_SYMBOL_GPL(filemap_fdatawrite_range_kick);
+EXPORT_SYMBOL_GPL(filemap_flush_range);
 
 /**
  * filemap_flush - mostly a non-blocking flush
@@ -470,10 +447,22 @@ EXPORT_SYMBOL_GPL(filemap_fdatawrite_range_kick);
  */
 int filemap_flush(struct address_space *mapping)
 {
-	return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
+	return filemap_flush_range(mapping, 0, LLONG_MAX);
 }
 EXPORT_SYMBOL(filemap_flush);
 
+/*
+ * Start writeback on @nr_to_write pages from @mapping.  No one but the existing
+ * btrfs caller should be using this.  Talk to linux-mm if you think adding a
+ * new caller is a good idea.
+ */
+int filemap_flush_nr(struct address_space *mapping, long *nr_to_write)
+{
+	return filemap_writeback(mapping, 0, LLONG_MAX, WB_SYNC_NONE,
+			nr_to_write);
+}
+EXPORT_SYMBOL_FOR_MODULES(filemap_flush_nr, "btrfs");
+
 /**
  * filemap_range_has_page - check if a page exists in range.
  * @mapping:           address space within which to check
@@ -691,8 +680,7 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 		return 0;
 
 	if (mapping_needs_writeback(mapping)) {
-		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+		err = filemap_fdatawrite_range(mapping, lstart, lend);
-						 WB_SYNC_ALL);
 		/*
 		 * Even if the above returned error, the pages may be
 		 * written partially (e.g. -ENOSPC), so we wait for it.
@@ -794,8 +782,7 @@ int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
 		return 0;
 
 	if (mapping_needs_writeback(mapping)) {
-		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+		err = filemap_fdatawrite_range(mapping, lstart, lend);
-						 WB_SYNC_ALL);
 		/* See comment of filemap_write_and_wait() */
 		if (err != -EIO)
 			__filemap_fdatawait_range(mapping, lstart, lend);
@@ -4528,16 +4515,8 @@ int filemap_invalidate_inode(struct inode *inode, bool flush,
 	unmap_mapping_pages(mapping, first, nr, false);
 
 	/* Write back the data if we're asked to. */
-	if (flush) {
+	if (flush)
-		struct writeback_control wbc = {
+		filemap_fdatawrite_range(mapping, start, end);
-			.sync_mode	= WB_SYNC_ALL,
-			.nr_to_write	= LONG_MAX,
-			.range_start	= start,
-			.range_end	= end,
-		};
-
-		filemap_fdatawrite_wbc(mapping, &wbc);
-	}
 
 	/* Wait for writeback to complete on all folios and discard. */
 	invalidate_inode_pages2_range(mapping, start / PAGE_SIZE, end / PAGE_SIZE);

mm/page-writeback.c

@@ -2434,12 +2434,6 @@ static bool folio_prepare_writeback(struct address_space *mapping,
 	return true;
 }
 
-static xa_mark_t wbc_to_tag(struct writeback_control *wbc)
-{
-	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
-		return PAGECACHE_TAG_TOWRITE;
-	return PAGECACHE_TAG_DIRTY;
-}
 
 static pgoff_t wbc_end(struct writeback_control *wbc)
 {