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

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Date:   Fri, 11 Jun 2021 08:17:02 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
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 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/
>
>   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.

—
Best Regards,
Yan, Zi

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