Subject: Re: [PATCH] mm: fix invalid node in alloc_migrate_target()
To: Xishi Qiu <qiuxishi@huawei.com>
References: <56F4E104.9090505@huawei.com>
 <20160325122237.4ca4e0dbca215ccbf4f49922@linux-foundation.org>
 <56F61EC8.7080508@huawei.com> <56FA5062.2020103@suse.cz>
 <56FA5AF5.30006@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Joonsoo Kim <js1304@gmail.com>,
        David Rientjes <rientjes@google.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Laura Abbott <lauraa@codeaurora.org>, zhuhui@xiaomi.com,
        wangxq10@lzu.edu.cn, Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dave Hansen <dave.hansen@intel.com>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <56FA732E.9020906@suse.cz>
Date: Tue, 29 Mar 2016 14:21:02 +0200
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On 03/29/2016 12:37 PM, Xishi Qiu wrote:
> On 2016/3/29 17:52, Vlastimil Babka wrote:
>> The code in this functions seems to come from 099730d67417d ("mm, hugetlb: use memory policy when available") by Dave Hansen (adding to CC), which was indeed merged in 4.4-rc1.
>>
>> However, alloc_pages_node() is only called in the block guarded by:
>>
>> if (!IS_ENABLED(CONFIG_NUMA) || !vma) {
>>
>> The rather weird "!IS_ENABLED(CONFIG_NUMA)" part comes from immediate followup commit e0ec90ee7e6f ("mm, hugetlbfs: optimize when NUMA=n")
>>
>> So I doubt the code path here can actually happen. But it's fragile and confusing nevertheless.
>>
>
> Hi Vlastimil
>
> __alloc_buddy_huge_page(h, NULL, addr, nid); // so the vma is NULL

Hm that's true, I got lost in the logic, thanks.
But the problem with dequeue_huge_page_node() is also IMHO true, and 
older, so we should fix 3.12+.