Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in move_page_tables()

From: Dmitry Osipenko <digetx@gmail.com>
To: Wei Yang <richardw.yang@linux.intel.com>,
	Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: akpm@linux-foundation.org, dan.j.williams@intel.com,
	aneesh.kumar@linux.ibm.com, kirill@shutemov.name,
	yang.shi@linux.alibaba.com, thellstrom@vmware.com,
	Thierry Reding <thierry.reding@gmail.com>,
	Jon Hunter <jonathanh@nvidia.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in move_page_tables()
Date: Tue, 28 Jan 2020 18:59:48 +0300	[thread overview]
Message-ID: <d66bb20e-c0e7-caef-cbbc-aa216c2be7d6@gmail.com> (raw)
In-Reply-To: <20200128004301.GD20624@richard>

28.01.2020 03:43, Wei Yang пишет:
> On Sun, Jan 26, 2020 at 05:47:57PM +0300, Dmitry Osipenko wrote:
>> 18.01.2020 02:22, Wei Yang пишет:
>>> Use the general helper instead of do it by hand.
>>>
>>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>>> ---
>>>  mm/mremap.c | 7 ++-----
>>>  1 file changed, 2 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/mm/mremap.c b/mm/mremap.c
>>> index c2af8ba4ba43..a258914f3ee1 100644
>>> --- a/mm/mremap.c
>>> +++ b/mm/mremap.c
>>> @@ -253,11 +253,8 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>>>  
>>>  	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
>>>  		cond_resched();
>>> -		next = (old_addr + PMD_SIZE) & PMD_MASK;
>>> -		/* even if next overflowed, extent below will be ok */
>>> +		next = pmd_addr_end(old_addr, old_end);
>>>  		extent = next - old_addr;
>>> -		if (extent > old_end - old_addr)
>>> -			extent = old_end - old_addr;
>>>  		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
>>>  		if (!old_pmd)
>>>  			continue;
>>> @@ -301,7 +298,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>>>  
>>>  		if (pte_alloc(new_vma->vm_mm, new_pmd))
>>>  			break;
>>> -		next = (new_addr + PMD_SIZE) & PMD_MASK;
>>> +		next = pmd_addr_end(new_addr, new_addr + len);
>>>  		if (extent > next - new_addr)
>>>  			extent = next - new_addr;
>>>  		move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
>>>
>>
>> Hello Wei,
>>
>> Starting with next-20200122, I'm seeing the following in KMSG on NVIDIA
>> Tegra (ARM32):
>>
>>  BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:190
>>
> 
> Thanks.
> 
> Would you mind letting me know which case you are testing?

Nothing special, systemd starts to fall apart during boot.

> Or the special thing is 32-bit platform?
I have a limited knowledge about mm/, so can't provide detailed explanation.

Please take a look at this:

[1]
https://elixir.bootlin.com/linux/v5.5/source/arch/arm/include/asm/pgtable-2level.h#L210

[2]
https://elixir.bootlin.com/linux/v5.5/source/include/asm-generic/pgtable.h#L549

[3]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c0ba10b512eb2e2a3888b6e6cc0e089f5e7a191b