linux-kernel - Re: [PATCH v4 07/11] iomap: fix iomap_dio

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Date: Thu, 25 Apr 2024 23:22:35 -0700
From: Christoph Hellwig <hch@...radead.org>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: willy@...radead.org, djwong@...nel.org, brauner@...nel.org,
	david@...morbit.com, chandan.babu@...cle.com,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	hare@...e.de, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-xfs@...r.kernel.org, mcgrof@...nel.org, gost.dev@...sung.com,
	p.raghav@...sung.com
Subject: Re: [PATCH v4 07/11] iomap: fix iomap_dio_zero() for fs bs > system
 page size

On Thu, Apr 25, 2024 at 01:37:42PM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@...sung.com>
> 
> iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> size < page_size. This is true for most filesystems at the moment.
> 
> If the block size > page size, this will send the contents of the page
> next to zero page(as len > PAGE_SIZE) to the underlying block device,
> causing FS corruption.
> 
> iomap is a generic infrastructure and it should not make any assumptions
> about the fs block size and the page size of the system.

So what happened to the plan to making huge_zero_page a folio and have
it available for non-hugetlb setups?  Not only would this be cleaner
and more efficient, but it would actually work for the case where you'd
have to zero more than 1MB on a 4k PAGE_SIZE system, which doesn't
seem impossible with 2MB folios.