linux-kernel - Re: [PATCH v3 14/21] iomap: Sub-extent zeroing

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Date: Tue, 11 Jun 2024 08:29:56 +0100
From: John Garry <john.g.garry@...cle.com>
To: Long Li <leo.lilong@...wei.com>, david@...morbit.com, djwong@...nel.org,
        hch@....de, viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
        chandan.babu@...cle.com, willy@...radead.org
Cc: axboe@...nel.dk, martin.petersen@...cle.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        ojaswin@...ux.ibm.com, ritesh.list@...il.com, mcgrof@...nel.org,
        p.raghav@...sung.com, linux-xfs@...r.kernel.org,
        catherine.hoang@...cle.com
Subject: Re: [PATCH v3 14/21] iomap: Sub-extent zeroing

On 11/06/2024 04:10, Long Li wrote:
>>   	if (need_zeroout) {
>> -		/* zero out from the start of the block to the write offset */
>> -		pad = pos & (fs_block_size - 1);
>> +		/* zero out from the start of the region to the write offset */
>> +		pad = pos & (zeroing_size - 1);
>>   		if (pad)
>>   			iomap_dio_zero(iter, dio, pos - pad, pad);
>   
> Hi, John
> 
> I've been testing and using your atomic write patch series recently. I noticed
> that if zeroing_size is larger than a single page, the length passed to
> iomap_dio_zero() could also be larger than a page size. This seems incorrect
> because iomap_dio_zero() utilizes ZERO_PAGE(0), which is only a single page
> in size.

ok, thanks for the notice.

So 
https://lore.kernel.org/linux-xfs/20240607145902.1137853-1-kernel@pankajraghav.com/T/#m7ba4ed4f0f0f48be99042703c10b42b72c9fe37c 
is changing that same function increase the zero range past PAGE_SIZE. 
I'll just need to figure out how to make it support an arbitrary larger 
size.

Thanks,
John