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Date: Mon, 22 Aug 2022 14:27:59 +0200
From: Christoph Hellwig <hch@lst.de>
To: Michal Hocko <mhocko@suse.com>
Cc: Christoph Hellwig <hch@lst.de>, iommu@lists.linux.dev,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	David Rientjes <rientjes@google.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] dma-pool: limit DMA and DMA32 zone size pools
Message-ID: <20220822122759.GA14932@lst.de>
References: <20220817060647.1032426-1-hch@lst.de> <20220817060647.1032426-4-hch@lst.de> <Yvzk2wE7ta+zSZOQ@dhcp22.suse.cz> <20220821104416.GC30530@lst.de> <YwNBHbYXpatJHD0K@dhcp22.suse.cz> <20220822111447.GA8935@lst.de> <YwNx6Q+FSwpKUOQ2@dhcp22.suse.cz>
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On Mon, Aug 22, 2022 at 02:09:13PM +0200, Michal Hocko wrote:
> OK, so you are worried about configurations that lack ZONE_DMA32 because
> that memory range is covered by ZONE_DMA? I thought though simply do not
> have CONFIG_ZONE_DMA32. Or am I wrong here?

Zones can disappear when they are empty.  Normally that affects
ZONE_NORMAL and ZONE_HIGHMEM, but it can also happen to ZONE_DMA32
when there is not enough memory.