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

[Chi Zhiling <chizhiling@163.com>]

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---