Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure.
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
References: <201801160115.w0G1FOIG057203@www262.sakura.ne.jp>
 <CA+55aFxOn5n4O2JNaivi8rhDmeFhTQxEHD4xE33J9xOrFu=7kQ@mail.gmail.com>
 <201801170233.JDG21842.OFOJMQSHtOFFLV@I-love.SAKURA.ne.jp>
 <CA+55aFyxyjN0Mqnz66B4a0R+uR8DdfxdMhcg5rJVi8LwnpSRfA@mail.gmail.com>
 <201801172008.CHH39543.FFtMHOOVSQJLFO@I-love.SAKURA.ne.jp>
 <201801181712.BFD13039.LtHOSVMFJQFOFO@I-love.SAKURA.ne.jp>
 <20180118122550.2lhsjx7hg5drcjo4@node.shutemov.name>
 <20180118131210.456oyh6fw4scwv53@node.shutemov.name>
 <4a6681a7-5ed6-ad9c-5d1d-73f1fcc82f3d@linux.intel.com>
 <20180118144514.njr5xdagtwzpzep6@node.shutemov.name>
Cc:     Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        torvalds@linux-foundation.org, kirill.shutemov@linux.intel.com,
        akpm@linux-foundation.org, hannes@cmpxchg.org,
        iamjoonsoo.kim@lge.com, mgorman@techsingularity.net,
        tony.luck@intel.com, vbabka@suse.cz, mhocko@kernel.org,
        aarcange@redhat.com, hillf.zj@alibaba-inc.com, hughd@google.com,
        oleg@redhat.com, peterz@infradead.org, riel@redhat.com,
        srikar@linux.vnet.ibm.com, vdavydov.dev@gmail.com,
        mingo@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        x86@kernel.org
From:   Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <b02e08bb-b551-e239-6f30-1db4587850c8@linux.intel.com>
Date:   Thu, 18 Jan 2018 06:51:37 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.0
MIME-Version: 1.0
In-Reply-To: <20180118144514.njr5xdagtwzpzep6@node.shutemov.name>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 01/18/2018 06:45 AM, Kirill A. Shutemov wrote:
> On Thu, Jan 18, 2018 at 06:38:10AM -0800, Dave Hansen wrote:
>> On 01/18/2018 05:12 AM, Kirill A. Shutemov wrote:
>>> -		if (pte_page(*pvmw->pte) - pvmw->page >=
>>> -				hpage_nr_pages(pvmw->page)) {
>> Is ->pte guaranteed to map a page which is within the same section as
>> pvmw->page?  Otherwise, with sparsemem (non-vmemmap), the pointer
>> arithmetic won't work.
> No, it's not guaranteed. It can be arbitrary page.
> 
> The arithmetic won't work because they are different "memory objects"?

No, because sections' mem_map[]s can be allocated non-contiguously.
Section 1's might be a lower virtual address than Section 0's.

They're allocated not unlike this:

	mem_section[0]->section_mem_map = kmalloc(SECTION_SIZE);
	mem_section[1]->section_mem_map = kmalloc(SECTION_SIZE);
	...

The first pfn in section 1 and the last pfn in section 0 are adjacent
PFNs, but their 'struct page' might have virtual addresses that are TB
apart.