Re: [PATCH 2/2] mm/page_alloc: Allow high-order pages to be stored on the per-cpu lists

[Mel Gorman]

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

  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@xxxxxxxxxxxxxxxxxxx>
---
 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) {