Messages in this thread | | | Date | Mon, 1 Jan 2007 03:39:49 +0900 | From | Paul Mundt <> | Subject | Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear_page()"? |
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On Sat, Dec 30, 2006 at 06:04:14PM -0500, Robert P. J. Day wrote: > fair enough. *technically*, not every call of the form > "memset(ptr,0,PAGE_SIZE)" necessarily represents an address that's on > a page boundary. but, *realistically*, i'm guessing most of them do. > just grabbing a random example from some grep output: > > arch/sh/mm/init.c: > ... > /* clear the zero-page */ > memset(empty_zero_page, 0, PAGE_SIZE); > ... > The problem with random grepping is that it doesn't give you any context. clear_page() isn't available in this case since we have a couple of different ways of implementing it, and the optimal approach is selected later on. There are also additional assumptions regarding alignment that don't allow clear_page() to be used directly as replacement for the memset() callsites (as has already been pointed out for some of the other architectures). While the empty_zero_page in this case sits on a full page boundary, others do not.
You might find some places in drivers that do this where you might be able to optimize things slightly with a clear_page() (or copy_page() in the memcpy() case), but it's going to need a lot of manual auditing rather than a find and replace. Any sort of wins you get out of this would be marginal at best, anyways.
The more interesting case would be page clustering/bulk page clearing with offload engines, and there's certainly room to build on the SGI patches for this. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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