Date: Tue, 09 Aug 2011 07:36:56 -0700 From: Chuck Swiger <cswiger@mac.com> To: Daniel Kalchev <daniel@digsys.bg> Cc: FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org> Subject: Re: 32GB limit per swap device? Message-ID: <935F8EC2-88E0-45A3-BE8B-7210BE223BC5@mac.com> In-Reply-To: <4E4143A6.6030307@digsys.bg> References: <4E4143A6.6030307@digsys.bg>
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On Aug 9, 2011, at 7:26 AM, Daniel Kalchev wrote: > I am trying to set up 64GB partitions for swap for a system that has 64GB of RAM (with the idea to dump kernel core etc). But, on 8-stable as of today I get: > > WARNING: reducing size to maximum of 67108864 blocks per swap unit > > Is there workaround for this limitation? Apparently, the 32GB swapspace limit is per swap area; you can add up to 4 swap areas so create two or three 32GB swap partitions. Regards, -- -Chuck PS: Older thread with some specific details: Begin forwarded message: > From: Matthew Dillon <dillon@apollo.backplane.com> > Date: August 5, 2008 11:29:21 AM PDT > To: Max Laier <max@love2party.net> > Cc: freebsd-stable@freebsd.org, Lin Jui-Nan Eric <ericlin@tamama.org> > Subject: Re: Max size of one swap slice > > :> Recently we found that we can only allocate 32GB for one swap slice. > :> Does there is any sysctl oid or any kernel option to increase it? Why > :> we have this restriction? > : > :this is a consequence of the data structure used to manage swap space. See > :sys/blist.h for details. It *seems* that you *might* be able to increase the > :coverage by decreasing BLIST_META_RADIX, but that's from a quick glance and > :most certainly not a good idea. > : > :However, the blist is a abstract enough API so that you can likely replace it > :with something that supports 64bit addresses (and thus 512*2^64 bytes of swap > :space per device) ... but I don't see why you'd want to do something like > :this. Remember that you need memory to manage your swap space as well! > : > :-- > :/"\ Best regards, | mlaier@freebsd.org > :\ / Max Laier | ICQ #67774661 > > The core structures can handle 2 billion swap pages == 2TB of swap, > but the blist code hits arithmatic overflows if a single blist has > more then (0x40000000 / BLIST_META_RADIX) = 1G/16 = 64M swap blocks, > or 256GB. > > I think the VM/BIO system had additional overflow issues due to > conversions back and forth between PAGE_SIZE and DEV_BSIZE which > further restricted the limit to 32GB. Those restrictions may be gone > now that FreeBSD is using 64 bit block numbers, so you may be able to > pop it up to 256GB with virtually no effort (but you need to test it > significantly!). > > With some work on the blist code only (not its structures) the arithmatic > overflow issues could also be resolved, increasing the swap capability > to 2TB. > > I do not recommend changing any of the core blist structure, particularly > not BLIST_META_RADIX. Just don't try :-). You do NOT want to bump > the swap block number fields to 64 bits. > > Also note that significant memory is used to manage that much swap. It's > a factor of 1:16384 or so for the blist structures and probably about > the same amount for the vm_object tracking structures. 32G of swap needs > around 2-4MB of wired ram. > > -Matt > Matthew Dillon > <dillon@backplane.com> > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org"
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