Re: + mm-hugetlb-fix-race-when-migrate-pages.patch added to -mm tree

From: Michal Hocko <mhocko@kernel.org>
To: zhong jiang <zhongjiang@huawei.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	akpm@linux-foundation.org, qiuxishi@huawei.com, vbabka@suse.cz,
	mm-commits@vger.kernel.org,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mel Gorman <mgorman@suse.de>,
	linux-mm@kvack.org
Subject: Re: + mm-hugetlb-fix-race-when-migrate-pages.patch added to -mm tree
Date: Thu, 21 Jul 2016 16:01:25 +0200	[thread overview]
Message-ID: <20160721140124.GN26379@dhcp22.suse.cz> (raw)
In-Reply-To: <5790D4FF.8070907@huawei.com>

On Thu 21-07-16 21:58:23, zhong jiang wrote:
> On 2016/7/21 21:40, Michal Hocko wrote:
> > On Thu 21-07-16 21:25:38, zhong jiang wrote:
> >> On 2016/7/21 20:55, Michal Hocko wrote:
> > [...]
> >>> OK, now I understand what you mean. So you mean that a different process
> >>> initiates the migration while this path copies to pte. That is certainly
> >>> possible but I still fail to see what is the problem about that.
> >>> huge_pte_alloc will return the identical pte whether it is regular or
> >>> migration one. So what exactly is the problem?
> >>>
> >> copy_hugetlb_page_range obtain the shared dst_pte, it may be not equal
> >> to the src_pte.  The dst_pte can come from other process sharing the
> >> mapping.
> > So you mean that the parent doesn't have the shared pte while the child
> > would get one?
> >  
>  no, parent must have the shared pte because the the child copy the
> parent. but parent is not the only source pte we can get. when we
> scan the maping->i_mmap, firstly ,it can obtain a shared pte from
> other process. but I am not sure.

But then all the shared ptes should be identical, no? Or am I missing
something?

-- 
Michal Hocko
SUSE Labs

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