[PATCH] iomap: add dirty page control to iomap_zero_iter

[Chi Zhiling <chizhiling@163.com>]

From: Chi Zhiling <chizhiling@kylinos.cn>

This patch prepares the iomap framework for exFAT's upcoming migration to
iomap. During testing of the exFAT iomap branch with xfstests generic/299
on a VM with 8GB RAM and a 40GB disk, system unresponsiveness was observed.

iomap_zero_iter() lacked dirty page throttling, which could cause memory
pressure when exFAT's valid_size mechanism triggers large-scale zeroing
operations during writes beyond valid_size.

Align iomap_zero_iter() with iomap_write_iter() by adding
balance_dirty_pages_ratelimited() to throttle dirty page generation during
large zeroing operations. Also add cond_resched() to provide voluntary
rescheduling points during long-running loops.

Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Cc: Namjae Jeon <linkinjeon@kernel.org>
---

exFAT iomap migration:
https://lore.kernel.org/linux-fsdevel/20260507124238.7313-1-linkinjeon@kernel.org/

 fs/iomap/buffered-io.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index d7b648421a70..f6955786c8ad 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1543,6 +1543,8 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
 		size_t offset;
 		bool ret;
 
+		balance_dirty_pages_ratelimited(iter->inode->i_mapping);
+
 		bytes = min_t(u64, SIZE_MAX, bytes);
 		status = iomap_write_begin(iter, write_ops, &folio, &offset,
 				&bytes);
@@ -1571,6 +1573,8 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
 		if (WARN_ON_ONCE(!ret))
 			return -EIO;
 
+		cond_resched();
+
 		status = iomap_iter_advance(iter, bytes);
 		if (status)
 			break;
-- 
2.43.0