Date: Mon, 7 Jun 2004 09:26:11 -0700 From: Peter Wemm <peter@wemm.org> To: Thomas Moestl <t.moestl@tu-bs.de> Cc: Kris Kennaway <kris@obsecurity.org> Subject: Re: HEADS UP! KSE needs more attention Message-ID: <200406070926.11289.peter@wemm.org> In-Reply-To: <20040607143332.GA1311@timesink.dyndns.org> References: <40C36D31.4010003@freebsd.org> <20040606215921.GA96205@xor.obsecurity.org> <20040607143332.GA1311@timesink.dyndns.org>
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On Monday 07 June 2004 07:33 am, Thomas Moestl wrote: > On Sun, 2004/06/06 at 14:59:21 -0700, Kris Kennaway wrote: > > On Sun, Jun 06, 2004 at 03:49:13PM -0600, Scott Long wrote: > > > amd64 is approaching critical mass for tier-1. There are a > > > number of developers that own amd64 hardware now, and a number of > > > users who are asking about it on the mailing lists. Peter is > > > finishing up the last blocking item for it (kld's) not including > > > the observed KSE problems. It's very close and I _will_ hold up > > > the release for it to get done. amd64 is the future of commodity > > > computing and we aren't going to ignore it for 5-STABLE. > > > > amd64 has a bug with swapping - when something begins to access > > swap, the entire system becomes almost entirely unresponsive (e.g. > > no mouse response for up to 10 seconds) until it stops. Peter has > > some ideas about it, but it's a serious enough bug that it forced > > me to stop using amd64 as my desktop machine (hello, kde!). > > Hmmm, I have encountered a similar problem on sparc64 once; the > reason was that vm_pageout_map_deactivate_pages() calls > pmap_remove() for the range from the start to the end of the > process's vm_map when a process is swapped out. Start and end > are VM_MIN_ADDRESS and VM_MAXUSER_ADDRESS respectively, and on > 64-bit architectures, that range is very large (128TB on ia64 > if I'm not mistaken), so the iteration in pmap_remove() must > be carefully designed to make as large steps as possible to > avoid long run times (or to not iterate over the range at all > if it becomes too large, which we did on sparc64). > > It seems that the amd64 version of pmap_remove() will essentially > always iterate in 2MB (level 2 page table) steps, regardless of > whether there is mapping for the respective level 2 table in the > table levels above; that means that in the previously mentioned case, > the outer loop will usually run for about 67 million iterations (the > resident count guard may not be of much use here if a stack page is > left at the very end of the address space). Since there are a few > memory accesses needed in each iterations, that may already be the > cause of such a delay. You know, this sounds spot-on! Thanks for the tip! -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5
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