From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Arcangeli Subject: Re: regression breaks lowmem reserved RAM Date: Tue, 1 Apr 2008 12:53:31 +0200 Message-ID: <20080401105331.GH12427@duo.random> References: <20080328194909.GA10617@duo.random> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, kvm-devel@lists.sourceforge.net, Jens Axboe To: Andrew Morton , Yang Shi Return-path: Content-Disposition: inline In-Reply-To: <20080328194909.GA10617@duo.random> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Looking a bit closer into this regression the reason this can't be right is that dma_addr common default is BLK_BOUNCE_HIGH and most machines have less than 4G. So if you do: if (b_pfn <= (min_t(u64, 0xffffffff, BLK_BOUNCE_HIGH) >> PAGE_SHIFT)) dma = 1 that will translate to: if (BLK_BOUNCE_HIGH <= BLK_BOUNCE_HIGH) dma = 1 So for 99% of hardware this will trigger unnecessary GFP_DMA allocations and isa pooling operations. Also note how the 32bit code still does b_pfn < blk_max_low_pfn. I guess this is what you were looking after. I didn't verify but as far as I can tell, this will stop the regression with isa dma operations at boot for 99% of blkdev/memory combinations out there and I guess this fixes the setups with >4G of ram and 32bit pci cards as well (this also retains symmetry with the 32bit code). Signed-off-by: Andrea Arcangeli diff --git a/block/blk-settings.c b/block/blk-settings.c index 1344a0e..5713f7e 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -140,7 +140,7 @@ void blk_queue_bounce_limit(struct request_queue *q, u64 dma_addr) /* Assume anything <= 4GB can be handled by IOMMU. Actually some IOMMUs can handle everything, but I don't know of a way to test this here. */ - if (b_pfn <= (min_t(u64, 0xffffffff, BLK_BOUNCE_HIGH) >> PAGE_SHIFT)) + if (b_pfn < (min_t(u64, 0x100000000UL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT)) dma = 1; q->bounce_pfn = max_low_pfn; #else