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Date: Tue, 1 Apr 2008 14:45:54 +0200 From: Jens Axboe <jens.axboe@...cle.com> To: Andrea Arcangeli <andrea@...ranet.com> Cc: Andrew Morton <akpm@...l.org>, Yang Shi <yang.shi@...driver.com>, linux-kernel@...r.kernel.org, kvm-devel@...ts.sourceforge.net Subject: Re: regression breaks lowmem reserved RAM On Tue, Apr 01 2008, Andrea Arcangeli wrote: > 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 <andrea@...ranet.com> Thanks Andrea, this looks much saner! -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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