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Date: Wed, 04 Mar 2009 21:37:43 -0500 (EST) From: Nicolas Pitre <nico@....org> To: Minchan Kim <minchan.kim@...il.com> Cc: lkml <linux-kernel@...r.kernel.org>, linux-mm@...ck.org, Russell King - ARM Linux <linux@....linux.org.uk> Subject: Re: [RFC] atomic highmem kmap page pinning On Thu, 5 Mar 2009, Minchan Kim wrote: > I thought kmap and dma_map_page usage was following. > > kmap(page); > ... > dma_map_page(...) > invalidate_cache_line > > kunmap(page); > > In this case, how do pkmap_count value for the page passed to dma_map_page become 1 ? > The caller have to make sure to complete dma_map_page before kunmap. The caller doesn't have to call kmap() on pages it intends to use for DMA. > Do I miss something ? See above. > > > As far as I understand, To make irq_disable to prevent this problem is > > > rather big cost. > > > > How big? Could you please elaborate on the significance of this cost? > > I don't have a number. It depends on you for submitting this patch. My assertion is that the cost is negligible. This is why I'm asking you why you think this is a big cost. Nicolas -- 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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