Date: Wed, 10 Aug 2011 09:38:36 +0000 From: Holger Kipp <Holger.Kipp@alogis.com> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org>, Daniel Kalchev <daniel@digsys.bg> Subject: Re: 32GB limit per swap device? Message-ID: <84407276-7546-4ABE-A0EE-A5E82E1CC358@alogis.com> In-Reply-To: <20110810084759.GA32346@icarus.home.lan> References: <4E4143A6.6030307@digsys.bg> <20110809151646.GF1814@albert.catwhisker.org> <4E422F8A.1070508@digsys.bg> <20110810074759.GA30254@icarus.home.lan> <4E423CAC.20008@digsys.bg> <CFE743A4-A5FA-4AC8-B090-E1174EB49473@alogis.com> <20110810084759.GA32346@icarus.home.lan>
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Am 10.08.2011 um 10:47 schrieb Jeremy Chadwick:
> On Wed, Aug 10, 2011 at 08:27:27AM +0000, Holger Kipp wrote:
>>
>> Am 10.08.2011 um 10:09 schrieb Daniel Kalchev:
>>
>>> On 10.08.11 10:47, Jeremy Chadwick wrote:
>>>> On Wed, Aug 10, 2011 at 10:13:14AM +0300, Daniel Kalchev wrote:
>>>>> I am more concerned that with 32GB of swap in single device I could n=
ot dump kernel core, with 64GB of RAM.
>>>> My apologies if I've misunderstood something, but why does this of any
>>>> concern? Machine has 64GB RAM. You have a single swap slice that's
>>>> effectively 32GB. How is a kernel panic worth of 64GB RAM going to fi=
t
>>>> into a 32GB swap slice?
>>>>
>>> The swap partitions are 64GB, it is only that FreeBSD refuses to use mo=
re than 32GB of each for swap. But.. it might happily dump core to the whol=
e partition, tests will show.
>>
>> I doubt it. Have you tried increasing kern.maxswzone? It is the size in =
KB (for 32GB it is set to 33554432).
>> kern.maxswzone: Maximum memory for swap metadata
>
> The variable is set to 32MBytes, not 32GBytes. The default size is
> defined as variable VM_SWZONE_SIZE_MAX, which is 32*1024*1024 per
> sys/i386/include/param.h and sys/amd64/include/param.h.
>
> Furthermore, this variable does not do what you're implying.
Ah, then I misinterpreted the output of "man loader" which states:
kern.maxswzone
Limits the amount of KVM to be used to hold swap meta
information, which directly governs the maximum amount o=
f
swap the system can support.
> So we're back to where we started: swap slices/partitions can be greater
> than 32GBytes in size, but "something" is limiting the maximum amount of
> memory which can be dumped to a single swap swap to 32GBytes.
Anyway, there is one thing in /usr/src/sys/vm/swap_pager.c (so if you get t=
his
warning (reducing size to maximum of... per swap unit)), this might be the
reason:
/*
* If we go beyond this, we get overflows in the radix
* tree bitmap code.
*/
mblocks =3D 0x40000000 / BLIST_META_RADIX;
if (nblks > mblocks) {
printf("WARNING: reducing size to maximum of %lu blocks per=
swap unit\n",
mblocks);
nblks =3D mblocks;
}
Hope this is of some help.
Best regards,
Holger
--
Holger Kipp
Diplom-Mathematiker
Senior Consultant
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