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Date: Thu, 24 Apr 2025 10:11:01 +0200
From: Christoph Hellwig <hch@lst.de>
To: Leon Romanovsky <leon@kernel.org>
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Subject: Re: [PATCH v9 10/24] mm/hmm: let users to tag specific PFN with
 DMA mapped bit
Message-ID: <20250424081101.GA22989@lst.de>
References: <cover.1745394536.git.leon@kernel.org> <0a7c1e06269eee12ff8912fe0da4b7692081fcde.1745394536.git.leon@kernel.org> <7185c055-fc9e-4510-a9bf-6245673f2f92@redhat.com> <20250423181706.GT1213339@ziepe.ca> <36891b0e-d5fa-4cf8-a181-599a20af1da3@redhat.com> <20250423233335.GW1213339@ziepe.ca> <20250424080744.GP48485@unreal>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, Apr 24, 2025 at 11:07:44AM +0300, Leon Romanovsky wrote:
> > I see, so yes order occupies 5 bits [-4,-5,-6,-7,-8] and the
> > DMA_MAPPED overlaps, it should be 9 not 7 because of the backwardness.
> 
> Thanks for the fix.

Maybe we can use the chance to make the scheme less fragile?  i.e.
put flags in the high bits and derive the first valid bit from the
pfn order?