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Date: Fri, 9 Oct 2026 09:37:18 -0600
From: Keith Busch <kbusch@kernel.org>
To: Adrian Huang12 <ahuang12@lenovo.com>
Cc: Christoph Hellwig <hch@lst.de>, John Garry <john.garry@linux.dev>,
	"sagi@grimberg.me" <sagi@grimberg.me>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	Jiwei JW10 Sun <sunjw10@lenovo.com>,
	"iommu@lists.linux.dev" <iommu@lists.linux.dev>
Subject: Re: [External] Re: [PATCH] Revert "nvme-pci: clamp max_hw_sectors
 based on DMA optimized limitation"
Message-ID: <askKLgBhLzjaOyfF@kbusch-mbp>
References: <20261006120248.147654-1-hch@lst.de>
 <8cf8a8ea-c9c9-434b-aec6-e361280a88a4@linux.dev>
 <20261008123724.GA22096@lst.de>
 <TPZP295MB0013C6E51C73799E49B8EFF4B3922@TPZP295MB0013.TWNP295.PROD.OUTLOOK.COM>
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On Fri, Oct 09, 2026 at 09:11:56AM +0000, Adrian Huang12 wrote:
> 
> BTW, with this reverted patch, I'm setting up the test environment to
> check whether the issue does not appear with a newer kernel that
> includes the updated IOMMU subsystem. I'll share the results by the
> end of next week.

It does sound like an IOMMU implementation issue if the revert regresses
your testing. Let's say the application wants to write 1MB of data:
we're DMA mapping the same total amount either way, so I don't think it
should have been more efficient for the driver to send eight 128k
mapping requests vs a single 1MB.