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Date: Tue, 2 Jul 2024 14:02:50 +0200
From: Christoph Hellwig <hch@lst.de>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: Christoph Hellwig <hch@lst.de>, david@fromorbit.com,
	willy@infradead.org, chandan.babu@oracle.com, djwong@kernel.org,
	brauner@kernel.org, akpm@linux-foundation.org,
	linux-kernel@vger.kernel.org, yang@os.amperecomputing.com,
	linux-mm@kvack.org, john.g.garry@oracle.com,
	linux-fsdevel@vger.kernel.org, hare@suse.de, p.raghav@samsung.com,
	mcgrof@kernel.org, gost.dev@samsung.com, cl@os.amperecomputing.com,
	linux-xfs@vger.kernel.org, Zi Yan <zi.yan@sent.com>
Subject: Re: [PATCH v8 06/10] iomap: fix iomap_dio_zero() for fs bs >
 system page size
Message-ID: <20240702120250.GA17373@lst.de>
References: <20240625114420.719014-1-kernel@pankajraghav.com> <20240625114420.719014-7-kernel@pankajraghav.com> <20240702074203.GA29410@lst.de> <20240702101556.jdi5anyr3v5zngnv@quentin>
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On Tue, Jul 02, 2024 at 10:15:56AM +0000, Pankaj Raghav (Samsung) wrote:
> Willy suggested we could use raw pages as we don't need the metadata
> from using a folio. [0]

Ok, that feels weird but I'll defer to his opinion in that case.

> > > +	/*
> > > +	 * Max block size supported is 64k
> > > +	 */
> > > +	WARN_ON_ONCE(len > ZERO_PAGE_64K_SIZE);
> > 
> > 
> > A WARN_ON without actually erroring out here is highly dangerous. 
> 
> I agree but I think we decided that we are safe with 64k for now as fs 
> that uses iomap will not have a block size > 64k. 
> 
> But this function needs some changes when we decide to go beyond 64k
> by returning error instead of not returning anything. 
> Until then WARN_ON_ONCE would be a good stop gap for people developing
> the feature to go beyond 64k block size[1]. 

Sure, but please make it return an error and return that instead of
just warning and going beyond the allocated page.