[PATCH] iomap: add dirty page control to iomap_zero_iter

[PATCH] iomap: add dirty page control to iomap_zero_iter

[Chi Zhiling]

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

Re: [PATCH] iomap: add dirty page control to iomap_zero_iter

[Christoph Hellwig]

On Sun, May 10, 2026 at 02:47:37PM +0800, Chi Zhiling wrote:
> 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.

The balance_dirty_pages_ratelimited looks good.  Now with lazy preempt
we really should not need more cond_resched calls, though.

> 
> 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
---end quoted text---

Re: [PATCH] iomap: add dirty page control to iomap_zero_iter

[Chi Zhiling]

On 5/11/26 16:57, Christoph Hellwig wrote:
> On Sun, May 10, 2026 at 02:47:37PM +0800, Chi Zhiling wrote:
>> 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.
> 
> The balance_dirty_pages_ratelimited looks good.  Now with lazy preempt
> we really should not need more cond_resched calls, though.

Okay, will drop it in next version.

Thanks,

> 
>>
>> 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
> ---end quoted text---