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Date: Thu, 25 Apr 2024 23:22:35 -0700
From: Christoph Hellwig <hch@infradead.org>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: willy@infradead.org, djwong@kernel.org, brauner@kernel.org,
	david@fromorbit.com, chandan.babu@oracle.com,
	akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org,
	hare@suse.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-xfs@vger.kernel.org, mcgrof@kernel.org, gost.dev@samsung.com,
	p.raghav@samsung.com
Subject: Re: [PATCH v4 07/11] iomap: fix iomap_dio_zero() for fs bs > system
 page size
Message-ID: <ZitIK5OnR7ZNY0IG@infradead.org>
References: <20240425113746.335530-1-kernel@pankajraghav.com>
 <20240425113746.335530-8-kernel@pankajraghav.com>
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In-Reply-To: <20240425113746.335530-8-kernel@pankajraghav.com>

On Thu, Apr 25, 2024 at 01:37:42PM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.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.