linux-kernel - Re: [PATCH v2 3/3] xfs: Let the max iomap length be consistent with the writeback code

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Message-ID: <ZwTSmHM4o8Gg5NRW@infradead.org>
Date: Mon, 7 Oct 2024 23:35:04 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Dave Chinner <david@...morbit.com>
Cc: Tang Yizhou <yizhou.tang@...pee.com>, jack@...e.cz, hch@...radead.org,
	willy@...radead.org, akpm@...ux-foundation.org,
	chandan.babu@...cle.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v2 3/3] xfs: Let the max iomap length be consistent with
 the writeback code

On Tue, Oct 08, 2024 at 08:36:02AM +1100, Dave Chinner wrote:
> I think this map size limiting is completely unnecessary for
> buffered writeback - buffered writes are throttled against writeback
> by balance_dirty_pages(), not by extent allocation size. The size of
> the delayed allocation or the overwrite map is largely irrelevant -
> we're going to map the entire range during a write, do it just
> doesn't matter what size the mapping is...

Yes.  This goes back all the way to your original iomap prototype,
but even back then balance_dirty_pages should have done all the
work.