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

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Date:   Tue, 20 Nov 2018 20:04:51 -0500 (EST)
From:   Pankaj Gupta <pagupta@...hat.com>
To:     David Hildenbrand <david@...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


> > >> ---
> > >>  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)
> 
> o.k
> > 
> > So PageOffline is completely managed by the page owner.
> 
> Makes sense. Thanks for explaining.

Looks good to me.

Acked-by: Pankaj gupta <pagupta@...hat.com>