linux-ext4 - Re: LBS support for EXT4

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Message-ID: <jcgnjl6txstun2hcimtz2zdayz7kxw4em6orafu5mfmcl2j5ik@ootfvveenf7j>
Date: Fri, 20 Jun 2025 17:55:58 +0200
From: Jan Kara <jack@...e.cz>
To: Pankaj Raghav <kernel@...kajraghav.com>
Cc: Jan Kara <jack@...e.cz>, tytso@....edu, 
	Luis Chamberlain <mcgrof@...nel.org>, Pankaj Raghav <p.raghav@...sung.com>, linux-ext4@...r.kernel.org, 
	Zhang Yi <yi.zhang@...weicloud.com>
Subject: Re: LBS support for EXT4

[added ext4 list and Zhang to CC]

Hi,

On Thu 19-06-25 15:05:14, Pankaj Raghav wrote:
> Hello Jan and Ted,
> 
> As you might know, I added LBS support to XFS sometime back. And after
> that Luis added LBS support to block devices/buffer head path.
> 
> And now that EXT4 supports large folios, it should be possible to add LBS
> support to EXT4.
> 
> I started digging in to the code, and it looks like it might require some
> rework throughout EXT4 and lot of testing.
> 
> My question is:
> 
> I have seen patches from Zhang Yi to add iomap buffered IO support to EXT4.
> If that happens, then adding LBS support should become trivial.
> 
> Do you think it might happen soon or it is going to take more time?
> Seeing the patches it is hard for me to say what the status is as the
> last patches posted for them was last year.

Well, time is always relative so it's difficult to tell what do you mean by
"soon" :). We are definitely interested in converting ext4 to iomap.
Currently we are fixing up some remaining issues caused by conversion to
support large order folios but after that iomap conversion would be a next
logical step. Zhang Yi had patches for that, I'm not sure how much from
them is left to apply after the large order folios have landed.

> The reason I am asking is, should I take up the challenge to add LBS
> support with buffer heads in EXT4, or should I wait until iomap patches
> are merged.

I think better spent time would be to help with the iomap conversion. I
don't think there will be that much coding left (perhaps some more exotic
features need attention) but there's definitely testing needed and review
is always welcome and most needed...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR