From: Jan Beulich <jbeulich@suse.com>
To: "Jürgen Groß" <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
Stefano Stabellini <sstabellini@kernel.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
stable@vger.kernel.org
Subject: Re: [PATCH] xen/balloon: Support xend-based toolstack take two
Date: Fri, 17 Jan 2020 12:36:50 +0100 [thread overview]
Message-ID: <4ddd12ae-94f7-0b16-346a-46e096d9ae6e@suse.com> (raw)
In-Reply-To: <dc509037-a7d6-caa5-8000-28aeb20b638e@suse.com>
On 17.01.2020 12:31, Jürgen Groß wrote:
> On 17.01.20 12:01, Jan Beulich wrote:
>> On 16.01.2020 18:00, Juergen Gross wrote:
>>> Commit 3aa6c19d2f38be ("xen/balloon: Support xend-based toolstack")
>>> tried to fix a regression with running on rather ancient Xen versions.
>>> Unfortunately the fix was based on the assumption that xend would
>>> just use another Xenstore node, but in reality only some downstream
>>> versions of xend are doing that. The upstream xend does not write
>>> that Xenstore node at all, so the problem must be fixed in another
>>> way.
>>>
>>> The easiest way to achieve that is to fall back to the behavior before
>>> commit 5266b8e4445c ("xen: fix booting ballooned down hvm guest")
>>> in case the static memory maximum can't be read.
>>
>> I could use some help here: Prior to said commit there was
>>
>> target_diff = new_target - balloon_stats.target_pages;
>>
>>
>> Which is, afaict, ...
>>
>>> --- a/drivers/xen/xen-balloon.c
>>> +++ b/drivers/xen/xen-balloon.c
>>> @@ -94,7 +94,7 @@ static void watch_target(struct xenbus_watch *watch,
>>> "%llu", &static_max) == 1))
>>> static_max >>= PAGE_SHIFT - 10;
>>> else
>>> - static_max = new_target;
>>> + static_max = balloon_stats.current_pages;
>>>
>>> target_diff = (xen_pv_domain() || xen_initial_domain()) ? 0
>>> : static_max - balloon_stats.target_pages;
>>
>> ... what the code does before your change. Afaict there was
>> never a use of balloon_stats.current_pages in this function.
>
> That is a little bit indirect, yes. In the end I want static_max to
> be either the maximum reported by Xen, or if not available, the current
> assumed memory size, which can be found in balloon_stats.current_pages.
>
> The main idea is to avoid a negative target_diff which would result in
> not ballooning down.
All understood. Yet the change is then not a restore of prior behavior
(just in a limited case), but a change to behavior that we never there
before. I.e. it was indeed my assumption that the code was right, but
the description was misleading.
Jan
next prev parent reply other threads:[~2020-01-17 11:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 17:00 [PATCH] xen/balloon: Support xend-based toolstack take two Juergen Gross
2020-01-16 19:32 ` Boris Ostrovsky
2020-01-17 11:01 ` Jan Beulich
2020-01-17 11:31 ` Jürgen Groß
2020-01-17 11:36 ` Jan Beulich [this message]
2020-01-17 11:45 ` Jürgen Groß
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=4ddd12ae-94f7-0b16-346a-46e096d9ae6e@suse.com \
--to=jbeulich@suse.com \
--cc=boris.ostrovsky@oracle.com \
--cc=jgross@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=sstabellini@kernel.org \
--cc=stable@vger.kernel.org \
--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).