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Wed, 20 Jan 2021 06:29:32 -0800 (PST) MIME-Version: 1.0 References: <20210120014333.222547-1-pasha.tatashin@soleen.com> <20210120014333.222547-11-pasha.tatashin@soleen.com> <20210120132223.GH4605@ziepe.ca> In-Reply-To: <20210120132223.GH4605@ziepe.ca> From: Pavel Tatashin Date: Wed, 20 Jan 2021 09:28:56 -0500 Message-ID: Subject: Re: [PATCH v6 10/14] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning To: Jason Gunthorpe Cc: LKML , linux-mm , Andrew Morton , Vlastimil Babka , Michal Hocko , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , Joonsoo Kim , mike.kravetz@oracle.com, Steven Rostedt , Ingo Molnar , Peter Zijlstra , Mel Gorman , Matthew Wilcox , David Rientjes , John Hubbard , Linux Doc Mailing List , Ira Weiny , linux-kselftest@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jan 20, 2021 at 8:22 AM Jason Gunthorpe wrote: > > On Tue, Jan 19, 2021 at 08:43:29PM -0500, Pavel Tatashin wrote: > > +.. note:: > > + Techniques that rely on long-term pinnings of memory (especially, RDMA and > > + vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory > > + hot remove. Pinned pages cannot reside on ZONE_MOVABLE, to guarantee that > > + memory can still get hot removed - be aware that pinning can fail even if > > + there is plenty of free memory in ZONE_MOVABLE. In addition, using > > + ZONE_MOVABLE might make page pinning more expensive, because pages have to be > > + migrated off that zone first. > > Just to point out, if anyone is using RDMA/etc with hotplug memory, > this series is likekly going to be a major regression for those users. Right: one is because we now prohibit pinning any pages in a movable zone, second reason is because we now check every page during migration that fixes an existing bug. > > Jason