[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Actual dom0 memory much lower than dom0_mem setting
- To: Andy Smith <andy@xxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxx
- From: Jürgen Groß <jgross@xxxxxxxx>
- Date: Wed, 8 Apr 2026 09:21:48 +0200
- Authentication-results: eu.smtp.expurgate.cloud; dkim=pass header.s=google header.d=suse.com header.i="@suse.com" header.h="In-Reply-To:Autocrypt:From:Content-Language:References:To:Subject:User-Agent:MIME-Version:Date:Message-ID"
- Autocrypt: addr=jgross@xxxxxxxx; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNH0p1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmNvbT7CwHkEEwECACMFAlOMcK8CGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRCw3p3WKL8TL8eZB/9G0juS/kDY9LhEXseh mE9U+iA1VsLhgDqVbsOtZ/S14LRFHczNd/Lqkn7souCSoyWsBs3/wO+OjPvxf7m+Ef+sMtr0 G5lCWEWa9wa0IXx5HRPW/ScL+e4AVUbL7rurYMfwCzco+7TfjhMEOkC+va5gzi1KrErgNRHH kg3PhlnRY0Udyqx++UYkAsN4TQuEhNN32MvN0Np3WlBJOgKcuXpIElmMM5f1BBzJSKBkW0Jc Wy3h2Wy912vHKpPV/Xv7ZwVJ27v7KcuZcErtptDevAljxJtE7aJG6WiBzm+v9EswyWxwMCIO RoVBYuiocc51872tRGywc03xaQydB+9R7BHPzsBNBFOMcBYBCADLMfoA44MwGOB9YT1V4KCy vAfd7E0BTfaAurbG+Olacciz3yd09QOmejFZC6AnoykydyvTFLAWYcSCdISMr88COmmCbJzn sHAogjexXiif6ANUUlHpjxlHCCcELmZUzomNDnEOTxZFeWMTFF9Rf2k2F0Tl4E5kmsNGgtSa aMO0rNZoOEiD/7UfPP3dfh8JCQ1VtUUsQtT1sxos8Eb/HmriJhnaTZ7Hp3jtgTVkV0ybpgFg w6WMaRkrBh17mV0z2ajjmabB7SJxcouSkR0hcpNl4oM74d2/VqoW4BxxxOD1FcNCObCELfIS auZx+XT6s+CE7Qi/c44ibBMR7hyjdzWbABEBAAHCwF8EGAECAAkFAlOMcBYCGwwACgkQsN6d 1ii/Ey9D+Af/WFr3q+bg/8v5tCknCtn92d5lyYTBNt7xgWzDZX8G6/pngzKyWfedArllp0Pn fgIXtMNV+3t8Li1Tg843EXkP7+2+CQ98MB8XvvPLYAfW8nNDV85TyVgWlldNcgdv7nn1Sq8g HwB2BHdIAkYce3hEoDQXt/mKlgEGsLpzJcnLKimtPXQQy9TxUaLBe9PInPd+Ohix0XOlY+Uk QFEx50Ki3rSDl2Zt2tnkNYKUCvTJq7jvOlaPd6d/W0tZqpyy7KVay+K4aMobDsodB3dvEAs6 ScCnh03dDAFgIq5nsB11j3KPKdVoPlfucX2c7kGNH+LUMbzqV6beIENfNexkOfxHfw==
- Delivery-date: Wed, 08 Apr 2026 07:22:33 +0000
- List-id: Xen user discussion <xen-users.lists.xenproject.org>
On 03.04.26 17:23, Andy Smith wrote:
Hi,
Something I noticed when looking into my previous issue: Despite
dom0_memory being set to 8192M on the hypervisor command line, and
ballooning being disabled, with Xen 4.20.2 dom0 comes up with only 6353M
available to it (according to "free -m").
So, aiming to get a usable 8192M dom0 memory, I bumped it up by the
shortfall of 1839M:
$ sudo xl info | grep xen_commandline
xen_commandline : placeholder dom0_mem=10031M dom0_max_vcpus=2
com1=115200,8n1,0x2f8,10 console=com1,vga ucode=scan smt=1 no-real-mode edd=off
$ free -m
total used free shared buff/cache
available
Mem: 7794 400 7286 12 228 7394
Swap: 1904 0 1904
I ended up with only 7794M. So it seems like the more memory I give
dom0, the bigger the shortfall gets.
It is predictable in that if I specify 10031M on this machine I always
end up with 7794M usable, but I can't predict what it will be ahead of
time so I don't know what to set it to in order to end up with 8192M.
This happens on other machines as well so I think it must be pretty
widespread.
This sort of thing has happened forever — well before Xen 4.14. Here's
an example from a different machine, slightly different hardware, Xen
4.14.5 with dom0 kernel 5.10.0-0.deb10.16-amd64 (very soon to be
reinstalled/upgraded!):
$ sudo xl info | grep xen_commandline
xen_commandline : placeholder dom0_mem=8192M dom0_max_vcpus=2
com1=115200,8n1,0x2f8,10 console=com1,vga ucode=scan smt=1
$ free -m
total used free shared buff/cache available
Mem: 6285 1425 3239 126 1620 4642
Swap: 952 1 951
Is this widely know and expected?
Is it fixable?
Is it something you can calculate? ("To get 8192M usable dom0 memory I
must specify…").
Some questions:
I would assume the memory size as reported by "xl list" is the configured one?
What does "cat /proc/iomem" in dom0 report?
Could you please post the output of "dmesg" after boot?
Juergen
Attachment:
OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key
Attachment:
OpenPGP_signature.asc
Description: OpenPGP digital signature
|
