linux-kernel - Re: [PATCH v1 4/5] xen/balloon: try to merge system ram resources

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Date:   Wed, 2 Sep 2020 12:34:12 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Jürgen Groß <jgross@...e.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        linux-hyperv@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Roger Pau Monné <roger.pau@...rix.com>,
        Julien Grall <julien@....org>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Baoquan He <bhe@...hat.com>,
        Wei Yang <richardw.yang@...ux.intel.com>
Subject: Re: [PATCH v1 4/5] xen/balloon: try to merge system ram resources



> Am 02.09.2020 um 12:15 schrieb Jürgen Groß <jgross@...e.com>:
> 
> On 21.08.20 12:34, David Hildenbrand wrote:
>> Let's reuse the new mechanism to merge system ram resources below the
>> root. We are the only one hotplugging system ram (e.g., DIMMs don't apply),
>> so this is safe to be used.
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> Cc: Juergen Gross <jgross@...e.com>
>> Cc: Stefano Stabellini <sstabellini@...nel.org>
>> Cc: Roger Pau Monné <roger.pau@...rix.com>
>> Cc: Julien Grall <julien@....org>
>> Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
>> Cc: Baoquan He <bhe@...hat.com>
>> Cc: Wei Yang <richardw.yang@...ux.intel.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>  drivers/xen/balloon.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index 37ffccda8bb87..5ec73f752b8a7 100644
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -338,6 +338,10 @@ static enum bp_state reserve_additional_memory(void)
>>      if (rc) {
>>          pr_warn("Cannot add additional memory (%i)\n", rc);
>>          goto err;
>> +    } else {
>> +        resource = NULL;
>> +        /* Try to reduce the number of system ram resources. */
>> +        merge_system_ram_resources(&iomem_resource);
>>      }
> 
> I don't see the need for setting resource to NULL and to use an "else"
> clause here.
> 

I set it to NULL because the pointer may be stale after that call - to avoid future bugs. But I can drop it.

Ack to the „else“ case.

Thanks for having a look!

> 
> Juergen
>