linux-kernel - Re: [PATCH v1 5/8] hv_balloon: mark inflated pages PG

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Date:   Tue, 20 Nov 2018 09:49:42 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Pankaj Gupta <pagupta@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, devel@...uxdriverproject.org,
        linux-fsdevel@...r.kernel.org, linux-pm@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        kexec-ml <kexec@...ts.infradead.org>, pv-drivers@...are.com,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Kairui Song <kasong@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v1 5/8] hv_balloon: mark inflated pages PG_offline

On 20.11.18 09:45, Pankaj Gupta wrote:
> 
> Hi David,
> 
>>
>> Mark inflated and never onlined pages PG_offline, to tell the world that
>> the content is stale and should not be dumped.
>>
>> Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
>> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
>> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
>> Cc: Kairui Song <kasong@...hat.com>
>> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Matthew Wilcox <willy@...radead.org>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: "Michael S. Tsirkin" <mst@...hat.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>  drivers/hv/hv_balloon.c | 14 ++++++++++++--
>>  1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
>> index 211f3fe3a038..47719862e57f 100644
>> --- a/drivers/hv/hv_balloon.c
>> +++ b/drivers/hv/hv_balloon.c
>> @@ -681,8 +681,13 @@ static struct notifier_block hv_memory_nb = {
>>  /* Check if the particular page is backed and can be onlined and online it.
>>  */
>>  static void hv_page_online_one(struct hv_hotadd_state *has, struct page *pg)
>>  {
>> -	if (!has_pfn_is_backed(has, page_to_pfn(pg)))
>> +	if (!has_pfn_is_backed(has, page_to_pfn(pg))) {
>> +		if (!PageOffline(pg))
>> +			__SetPageOffline(pg);
>>  		return;
>> +	}
>> +	if (PageOffline(pg))
>> +		__ClearPageOffline(pg);
>>  
>>  	/* This frame is currently backed; online the page. */
>>  	__online_page_set_limits(pg);
>> @@ -1201,6 +1206,7 @@ static void free_balloon_pages(struct hv_dynmem_device
>> *dm,
>>  
>>  	for (i = 0; i < num_pages; i++) {
>>  		pg = pfn_to_page(i + start_frame);
>> +		__ClearPageOffline(pg);
> 
> Just thinking, do we need to care for clearing PageOffline flag before freeing
> a balloon'd page?

Yes we have to otherwise the code will crash when trying to set PageBuddy.

(only one page type at a time may be set right now, and it makes sense.
A page that is offline cannot e.g. be a buddy page)

So PageOffline is completely managed by the page owner.

> 
> Thanks,
> Pankaj


-- 

Thanks,

David / dhildenb