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Date: Thu, 30 Nov 2023 10:57:28 +0530
From: Ritesh Harjani (IBM) <>
To: Christoph Hellwig <>
Cc: Christoph Hellwig <>, Jan Kara <>,,
Subject: Re: [RFC 2/3] ext2: Convert ext2 regular file buffered I/O to use iomap

Christoph Hellwig <> writes:

> On Thu, Nov 30, 2023 at 08:54:31AM +0530, Ritesh Harjani wrote:
>> So I took a look at this. Here is what I think -
>> So this is useful of-course when we have a large folio. Because
>> otherwise it's just one block at a time for each folio. This is not a
>> problem once FS buffered-io handling code moves to iomap (because we
>> can then enable large folio support to it).
> Yes.
>> However, this would still require us to pass a folio to ->map_blocks
>> call to determine the size of the folio (which I am not saying can't be
>> done but just stating my observations here).
> XFS currently maps based on the underlyig reservation (delalloc extent)
> and not the actual map size.   This works because on-disk extents are
> allocated as unwritten extents, and only the actual written part is
> the converted.  But if you only want to allocate blocks for the part
> actually written you actually need to pass in the dirty range and not
> just use the whole folio.  This would be the incremental patch to do
> that:

yes. dirty range indeed.

> But unless your block allocator is very cheap doing what XFS does is
> probably going to work much better.
>> ...ok so here is the PoC for seq counter check for ext2. Next let me
>> try to see if we can lift this up from the FS side to iomap - 
> This looks good to me from a very superficial view.  Dave is the expert
> on this, though.


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