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Date:   Fri, 11 Jun 2021 14:58:43 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Zi Yan <ziy@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 2/2] mm/page_alloc: Allow high-order pages to be stored
 on the per-cpu lists

On Fri, Jun 11, 2021 at 08:17:02AM -0400, Zi Yan wrote:
> On 11 Jun 2021, at 4:34, Mel Gorman wrote:
> 
> > On Thu, Jun 10, 2021 at 07:40:47AM -0400, Zi Yan wrote:
> >>>> qemu-system-x86_64 -kernel ~/repos/linux-1gb-thp/arch/x86/boot/bzImage \
> >>>>     -drive file=~/qemu-image/vm.qcow2,if=virtio \
> >>>>     -append "nokaslr root=/dev/vda1 rw console=ttyS0 " \
> >>>>     -pidfile vm.pid \
> >>>>     -netdev user,id=mynet0,hostfwd=tcp::11022-:22 \
> >>>>     -device virtio-net-pci,netdev=mynet0 \
> >>>>     -m 16g -smp 6 -cpu host -enable-kvm -nographic \
> >>>>     -machine hmat=on -object memory-backend-ram,size=8g,id=m0 \
> >>>>     -object memory-backend-ram,size=8g,id=m1 \
> >>>>     -numa node,memdev=m0,nodeid=0 -numa node,memdev=m1,nodeid=1
> >>>>
> >>>> The attached config has THP disabled. The VM cannot boot with THP enabled,
> >>>> either.
> >>>>
> >>>
> >>> There is not a lot of information to go on here. Can you confirm that a
> >>> revert of that specific patch from mmotm-2021-06-07-18-33 also boots? It
> >>> sounds like your console log is empty, does anything useful appear if
> >>> you add "earlyprintk=serial,ttyS0,115200" to the kernel command line?
> >>
> >> Sure. I can confirm that reverting the patch makes the VM boot.
> >> The important information I forgot to mention is that after I remove
> >> the NUMA setting in the QEMU, the VM can boot too.
> >>
> >> earlyprintk gave the error message (page out of zone boundary) when the VM could not boot:
> >>
> >
> > Can you test with the following patch please?
> >
> > --8<---
> > mm/page_alloc: Allow high-order pages to be stored on the per-cpu lists -fix
> >
> > Zi Ya reported the following problem
> s/Zi Ya/Zi Yan/

Sorry about that typo.

> >
> >   I am not able to boot my QEMU VM with v5.13-rc5-mmotm-2021-06-07-18-33.
> >   git bisect points to this patch. The VM got stuck at "Booting from ROM"
> >
> > "This patch" is "mm/page_alloc: Allow high-order pages to be stored on
> > the per-cpu lists" and earlyprintk showed the following
> >
> >   [    0.161237] Memory: 16396772K/16776684K available (18452K kernel code, 3336K rwdata, 8000K rodata, 1852K init, 1444K bss, 379656K reserved, 0K cma-reserve)
> >   [    0.162451] page 0x100041 outside node 1 zone Normal [ 0x240000 - 0x440000 ]
> >   [    0.163057] page:(____ptrval____) refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x100041
> >
> > The patch is allowing pages from different zones to exist on the PCP
> > lists which is not allowed. Review found two problems -- first, the
> > bulk allocator is not using the correct PCP lists. It happens to work
> > because it's order-0 only but it's wrong. The real problem is that the
> > boot pagesets can store free pages which is not allowed.
> >
> > Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> > ---
> >  mm/page_alloc.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index d6d90f046c94..8472bae567f0 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3625,7 +3625,15 @@ struct page *__rmqueue_pcplist(struct zone *zone, unsigned int order,
> >  			int batch = READ_ONCE(pcp->batch);
> >  			int alloced;
> >
> > -			batch = max(batch >> order, 2);
> > +			/*
> > +			 * Scale batch relative to order if batch implies
> > +			 * free pages can be stored on the PCP. Batch can
> > +			 * be 1 for small zones or for boot pagesets which
> > +			 * should never store free pages as the pages may
> > +			 * belong to arbitrary zones.
> > +			 */
> > +			if (batch > 1)
> > +				batch = max(batch >> order, 2);
> >  			alloced = rmqueue_bulk(zone, order,
> >  					batch, list,
> >  					migratetype, alloc_flags);
> > @@ -5265,7 +5273,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
> >  	/* Attempt the batch allocation */
> >  	local_lock_irqsave(&pagesets.lock, flags);
> >  	pcp = this_cpu_ptr(zone->per_cpu_pageset);
> > -	pcp_list = &pcp->lists[ac.migratetype];
> > +	pcp_list = &pcp->lists[order_to_pindex(ac.migratetype, 0)];
> >
> >  	while (nr_populated < nr_pages) {
> 
> Yes. This patch solves the issue. Thanks.
> 

Thanks. As Andrew dropped the patch from mmotm, I've send a v2 with the
fix included. Thanks for reporting and testing!

-- 
Mel Gorman
SUSE Labs

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