Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 15 Jan 2021 14:40:06 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Pavel Tatashin <pasha.tatashin@soleen.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@suse.com>,
        David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Sasha Levin <sashal@kernel.org>,
        Tyler Hicks <tyhicks@linux.microsoft.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, mike.kravetz@oracle.com,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Matthew Wilcox <willy@infradead.org>,
        David Rientjes <rientjes@google.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        Ira Weiny <ira.weiny@intel.com>,
        linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v4 08/10] mm/gup: limit number of gup migration failures,
 honor failures
Message-ID: <20210115184006.GH4605@ziepe.ca>
References: <20201217185243.3288048-1-pasha.tatashin@soleen.com>
 <20201217185243.3288048-9-pasha.tatashin@soleen.com>
 <20201217205048.GL5487@ziepe.ca>
 <CA+CK2bA4F+SipkReJzFjCSC-8kZdK4yrwCQZM+TvCTrqV2CGHg@mail.gmail.com>
 <20201218141927.GM5487@ziepe.ca>
 <CA+CK2bDULopw649ndBybA-ST5EoRMHULwcfQcSQVKT9r8zAtwQ@mail.gmail.com>
 <20210113195528.GD4605@ziepe.ca>
 <CA+CK2bDDUMOeCH8rQBL7fBdHCAUZBOykyXNL2N=hmxq7xi0giQ@mail.gmail.com>
 <CA+CK2bC=o1-qW5+d-Lud9qN1937PC4Jxf_oyxwVrKby=mH5WyQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CA+CK2bC=o1-qW5+d-Lud9qN1937PC4Jxf_oyxwVrKby=mH5WyQ@mail.gmail.com>
Precedence: bulk

On Fri, Jan 15, 2021 at 01:10:27PM -0500, Pavel Tatashin wrote:

> I've been thinking about this some more. Again, I am not sure this is
> a bug. I understand split_huge_pmd() may split the PMD size page into
> PTEs and leave the compound page intact. However, in order for pages[]
> to have non sequential addresses in compound page, those PTEs must
> also be migrated after split_huge_pmd(), 

Why focus on migrated? Anything could happen to those PTEs: they could
be COW'd, they could be mmap/munmap'd, etc.

Jason