Re: [PATCH] mm: Fix for PG_reserved page flag clearing

[Michal Hocko <mhocko@suse.com>]

On Mon 19-02-18 14:11:03, Masayoshi Mizuma wrote:
> Hello Michal, 
> 
> Mon, 19 Feb 2018 18:19:16 +0100 Michal Hocko wrote:
> > On Mon 19-02-18 12:06:14, Masayoshi Mizuma wrote:
> >> From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> >>
> >> struct page is inizialized as zero in __init_single_page().
> >> If the page is offlined page, PG_reserved flag is set in early boot
> >> time before __init_single_page(), so we should not clear the flag.
> >>
> >> The real problem is that we can not online the offlined page
> >> through following sysfs operation because offlined page is
> >> expected PG_reserved flag is set. 
> >> It is not needed the initialization, so remove it simply.
> >>
> >>   Code:
> >>
> >>   static int online_pages_range(unsigned long start_pfn, 
> >>   ...
> >>           if (PageReserved(pfn_to_page(start_pfn))) <= HERE!!
> >>                   for (i = 0; i < nr_pages; i++) {
> >>                           page = pfn_to_page(start_pfn + i);
> >>                           (*online_page_callback)(page);
> >>                           onlined_pages++;
> >>   sysfs operation:
> >>
> >>   # echo online > /sys/devices/system/node/node2/memory12288/online
> >>   # cat /sys/devices/system/node/node2/memory12288/online 
> >>   1
> >>   # cat /sys/devices/system/node/node2/meminfo 
> >>   Node 2 MemTotal:              0 kB
> > 
> > Nack. The patch is simply wrong. We do need to zero page for the boot
> > pages. I believe the fix you are looking for is 9bb5a391f9a5 ("mm,
> > memory_hotplug: fix memmap initialization"). Or do you still see a
> > problem with this patch applied?
> 
> I have confirmed the problem is fixed by your patch 9bb5a391f9a5.
> (I had tested it in 4.15.2, so I did not notice your patch, sorry)

I have posted the backport for the 4.15 stable tree just an hour ago so
it should appear in the next stable release.

Thanks for double checking.
-- 
Michal Hocko
SUSE Labs

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