RE: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages

[Ran Wang <ran.wang_1@nxp.com>]

Hi Michal,

> -----Original Message-----
> From: Michal Hocko [mailto:mhocko@kernel.org]
> Sent: Monday, November 13, 2017 7:03 PM
> To: Ran Wang <ran.wang_1@nxp.com>
> Cc: linux-mm@kvack.org; Michael Ellerman <mpe@ellerman.id.au>; Vlastimil
> Babka <vbabka@suse.cz>; Andrew Morton <akpm@linux-foundation.org>;
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>; Reza Arbab
> <arbab@linux.vnet.ibm.com>; Yasuaki Ishimatsu <yasu.isimatu@gmail.com>;
> qiuxishi@huawei.com; Igor Mammedov <imammedo@redhat.com>; Vitaly
> Kuznetsov <vkuznets@redhat.com>; LKML <linux-kernel@vger.kernel.org>;
> Leo Li <leoyang.li@nxp.com>; Xiaobo Xie <xiaobo.xie@nxp.com>
> Subject: Re: [PATCH 1/2] mm: drop migrate type checks from
> has_unmovable_pages
> 
> On Mon 13-11-17 07:33:13, Ran Wang wrote:
> > Hello Michal,
> >
> > <snip>
> >
> > > Date: Fri, 13 Oct 2017 14:00:12 +0200
> > >
> > > From: Michal Hocko <mhocko@suse.com>
> > >
> > > Michael has noticed that the memory offline tries to migrate kernel
> > > code pages when doing  echo 0 >
> > > /sys/devices/system/memory/memory0/online
> > >
> > > The current implementation will fail the operation after several
> > > failed page migration attempts but we shouldn't even attempt to
> > > migrate that memory and fail right away because this memory is
> > > clearly not migrateable. This will become a real problem when we drop
> the retry loop counter resp. timeout.
> > >
> > > The real problem is in has_unmovable_pages in fact. We should fail
> > > if there are any non migrateable pages in the area. In orther to
> > > guarantee that remove the migrate type checks because
> > > MIGRATE_MOVABLE is not guaranteed to contain only migrateable pages.
> It is merely a heuristic.
> > > Similarly MIGRATE_CMA does guarantee that the page allocator doesn't
> > > allocate any non-migrateable pages from the block but CMA
> > > allocations themselves are unlikely to migrateable. Therefore remove
> both checks.
> > >
> > > Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> > > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > > Tested-by: Michael Ellerman <mpe@ellerman.id.au>
> > > Acked-by: Vlastimil Babka <vbabka@suse.cz>
> > > ---
> > >  mm/page_alloc.c | 3 ---
> > >  1 file changed, 3 deletions(-)
> > >
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c index
> > > 3badcedf96a7..ad0294ab3e4f 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -7355,9 +7355,6 @@ bool has_unmovable_pages(struct zone *zone,
> > > struct page *page, int count,
> > >  	 */
> > >  	if (zone_idx(zone) == ZONE_MOVABLE)
> > >  		return false;
> > > -	mt = get_pageblock_migratetype(page);
> > > -	if (mt == MIGRATE_MOVABLE || is_migrate_cma(mt))
> > > -		return false;
> >
> > This drop cause DWC3 USB controller fail on initialization with
> > Layerscaper processors (such as LS1043A) as below:
> >
> > [    2.701437] xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned
> bus number 1
> > [    2.710949] cma: cma_alloc: alloc failed, req-size: 1 pages, ret: -16
> > [    2.717411] xhci-hcd xhci-hcd.0.auto: can't setup: -12
> > [    2.727940] xhci-hcd xhci-hcd.0.auto: USB bus 1 deregistered
> > [    2.733607] xhci-hcd: probe of xhci-hcd.0.auto failed with error -12
> > [    2.739978] xhci-hcd xhci-hcd.1.auto: xHCI Host Controller
> >
> > And I notice that someone also reported to you that DWC2 got affected
> > recently, so do you have the solution now?
> 
> Yes. It should be in linux-next. Have a look at the following email
> thread:
> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flkml.
> kernel.org%2Fr%2F20171104082500.qvzbb2kw4suo6cgy%40dhcp22.suse.cz&
> data=02%7C01%7Cran.wang_1%40nxp.com%7C5e73c6a941fc4f1c10e708d52
> a860c5b%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C636461677
> 583607877&sdata=zlRxJ4LZwOBsit5qRx9yFT5qfP54wZ0z6G1z%2Bcywf5g%3D
> &reserved=0

Thanks for your info, although I fail to open the link you shared, but I got patch
from my colleague and the issue got fix on my side, let you know, thanks.

Best Regards,
Ran
> --
> Michal Hocko
> SUSE Labs

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