[PATCH 0/5] Cache coherent device memory (CDM) with HMM v4

From: JÃrÃme Glisse
Date: Wed Jul 12 2017 - 14:06:17 EST

Changes since v3:
- change name to device host (s/DEVICE_PUBLIC/DEVICE_HOST/)
- added comments about how such memory is accounted (rss and memcg)
- added a documentation patch (to explain rss and memcg choice)
- add proper include to migrate.c and drop #if/#endif
- fix missing #if/#endif so this works even if DEVICE_PRIVATE is
not enabled

Git tree:

Cache coherent device memory apply to architecture with system bus
like CAPI or CCIX. Device connected to such system bus can expose
their memory to the system and allow cache coherent access to it
from the CPU.

Even if for all intent and purposes device memory behave like regular
memory, we still want to manage it in isolation from regular memory.
Several reasons for that, first and foremost this memory is less
reliable than regular memory if the device hangs because of invalid
commands we can loose access to device memory. Second CPU access to
this memory is expected to be slower than to regular memory. Third
having random memory into device means that some of the bus bandwith
wouldn't be available to the device but would be use by CPU access.

This is why we want to manage such memory in isolation from regular
memory. Kernel should not try to use this memory even as last resort
when running out of memory, at least for now.

This patchset add a new type of ZONE_DEVICE memory (DEVICE_HOST)
that is use to represent CDM memory. This patchset build on top of
the HMM patchset that already introduce a new type of ZONE_DEVICE
memory for private device memory (see HMM patchset).

The end result is that with this patchset if a device is in use in
a process you might have private anonymous memory or file back
page memory using ZONE_DEVICE (DEVICE_HOST). Thus care must be
taken to not overwritte lru fields of such pages.

Hence all core mm changes are done to address assumption that any
process memory is back by a regular struct page that is part of
the lru. ZONE_DEVICE page are not on the lru and the lru pointer
of struct page are use to store device specific informations.

Thus this patchset update all code path that would make assumptions
about lruness of a process page.

patch 01 - add DEVICE_HOST type to ZONE_DEVICE (all core mm changes)
patch 02 - add an helper to HMM for hotplug of CDM memory
patch 03 - preparatory patch for memory controller changes (memch)
patch 04 - update memory controller to properly handle
ZONE_DEVICE pages when uncharging
patch 05 - documentation patch

Previous posting:
v1 https://lkml.org/lkml/2017/4/7/638
v2 https://lwn.net/Articles/725412/
v3 https://lwn.net/Articles/727114/

JÃrÃme Glisse (5):
mm/device-host-memory: device memory cache coherent with CPU v3
mm/hmm: add new helper to hotplug CDM memory region v2
mm/memcontrol: allow to uncharge page without using page->lru field
mm/memcontrol: support MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_HOST v2
mm/hmm: documents how device memory is accounted in rss and memcg

Documentation/vm/hmm.txt | 40 ++++++++
fs/proc/task_mmu.c | 2 +-
include/linux/hmm.h | 7 +-
include/linux/ioport.h | 1 +
include/linux/memremap.h | 21 +++++
include/linux/mm.h | 20 ++--
kernel/memremap.c | 17 +++-
mm/Kconfig | 11 +++
mm/gup.c | 7 ++
mm/hmm.c | 89 ++++++++++++++++--
mm/madvise.c | 2 +-
mm/memcontrol.c | 231 ++++++++++++++++++++++++++++++-----------------
mm/memory.c | 46 +++++++++-
mm/migrate.c | 57 +++++++-----
mm/swap.c | 11 +++
15 files changed, 431 insertions(+), 131 deletions(-)