From: George Dunlap <George.Dunlap@eu.citrix.com>
To: Wei Liu <wei.liu2@citrix.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Ian Jackson <ian.jackson@eu.citrix.com>
Subject: Re: [PATCH for-4.7] libxl: keep PoD target adjustment by memory fudge after reload_domain_config()
Date: Tue, 31 May 2016 19:36:57 +0100 [thread overview]
Message-ID: <CAFLBxZa98Ysuep+9uEvAHuSptEkibeRqFBtBB0jEwXd4DwKtug@mail.gmail.com> (raw)
In-Reply-To: <1464716523-29663-1-git-send-email-wei.liu2@citrix.com>
On Tue, May 31, 2016 at 6:42 PM, Wei Liu <wei.liu2@citrix.com> wrote:
> From: Vitaly Kuznetsov <vkuznets@redhat.com>
>
> Commit 56fb5fd623 ("libxl: adjust PoD target by memory fudge, too")
> introduced target_memkb adjustment for HVM PoD domains on create. The
> adjustment is however being reset on reload_domain_config() (e.g. when
> we reboot the guest).
It was determined that all of the following...
> For example:
>
> I'm trying to create HVM PoD domain with the following settings:
> memory=1024
> maxmem=4096
> When the domain boots for the first time I see the following in Xen:
>
> (XEN) nr_pages=262145 ... max_pages=262400 (looks good)
>
> When I reboot the domain I see the following:
> (XEN) nr_pages=261889 ... max_pages=262144 (oops)
>
> After second reboot:
> (XEN) nr_pages=261633 ... max_pages=261888 (even less)
>
> And eventually the domain crashes with "p2m_pod_demand_populate: Dom4 out of
> PoD memory! (tot=261377 ents=787200 dom4)".
has actually nothing to do with this patch; and that actually,
contrary to the description above, the problem is that the adjustment
is *not* being reset.
A better description would be something like this:
---
Commit 56fb5fd623 ("libxl: adjust PoD target by memory fudge, too")
introduced target_memkb adjustment for HVM PoD domains on create,
wherein
the value it wrote to target is always 1MiB lower than the actual
target_memkb. Unfortunately, on reboot, it is this value which is
read *unmodified* to feed into the next domain creation; from which
1MiB is subtracted *again*. This means that any guest which reboots
with memory < maxmem will have its memory target decreased by 1MiB on
every boot.
This patch makes it so that when reading target on reboot, we adjust
the value we read *up* by 1MiB, so that the domain will be build with
the appropriate amount of memory and the target will remain the same
after reboot.
This is still not quite a complete fix, as the 1MiB offset is only
subtracted when creating or rebooting; it is not subtracted when 'xl
set-memory' is called. But it will prevent any situations where
memory is continually increased or decreased. A better fix will have
to wait until after the release.
---
-George
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-05-31 18:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-31 17:42 [PATCH for-4.7] libxl: keep PoD target adjustment by memory fudge after reload_domain_config() Wei Liu
2016-05-31 18:36 ` George Dunlap [this message]
2016-06-01 8:29 ` Vitaly Kuznetsov
2016-06-01 8:41 ` Wei Liu
2016-06-01 15:48 ` Ian Jackson
2016-06-01 15:56 ` Wei Liu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAFLBxZa98Ysuep+9uEvAHuSptEkibeRqFBtBB0jEwXd4DwKtug@mail.gmail.com \
--to=george.dunlap@eu.citrix.com \
--cc=ian.jackson@eu.citrix.com \
--cc=vkuznets@redhat.com \
--cc=wei.liu2@citrix.com \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).