Re: [PATCH v6 10/14] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning
From: Pavel Tatashin <pasha.tatashin@soleen.com>
Date: 2021-01-20 14:54:02
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linux-kselftest, linux-mm, lkml
On Wed, Jan 20, 2021 at 8:22 AM Jason Gunthorpe [off-list ref] wrote:
On Tue, Jan 19, 2021 at 08:43:29PM -0500, Pavel Tatashin wrote:quoted
+.. 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