linux-kernel - Re: [PATCH 0/6] Cache coherent device memory (CDM) with HMM v5

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Date:   Tue, 18 Jul 2017 11:26:51 +0800
From:   Bob Liu <liubo95@...wei.com>
To:     Jérôme Glisse <jglisse@...hat.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
CC:     John Hubbard <jhubbard@...dia.com>,
        David Nellans <dnellans@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Balbir Singh <bsingharora@...il.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH 0/6] Cache coherent device memory (CDM) with HMM v5

On 2017/7/14 5:15, Jérôme Glisse wrote:
> Sorry i made horrible mistake on names in v4, i completly miss-
> understood the suggestion. So here i repost with proper naming.
> This is the only change since v3. Again sorry about the noise
> with v4.
> 
> Changes since v4:
>   - s/DEVICE_HOST/DEVICE_PUBLIC
> 
> Git tree:
> https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-cdm-v5
> 
> 
> 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.
>

I think set a very large node distance for "Cache Coherent Device Memory" may be a easier way to address these concerns.

--
Regards,
Bob Liu


 
> 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 - rename DEVICE_PUBLIC to DEVICE_HOST to free DEVICE_PUBLIC name
> patch 02 - add DEVICE_PUBLIC type to ZONE_DEVICE (all core mm changes)
> patch 03 - add an helper to HMM for hotplug of CDM memory
> patch 04 - preparatory patch for memory controller changes (memch)
> patch 05 - update memory controller to properly handle
>            ZONE_DEVICE pages when uncharging
> patch 06 - 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/
> v4 https://lwn.net/Articles/727692/
> 
> Jérôme Glisse (6):
>   mm/zone-device: rename DEVICE_PUBLIC to DEVICE_HOST
>   mm/device-public-memory: device memory cache coherent with CPU v4
>   mm/hmm: add new helper to hotplug CDM memory region v3
>   mm/memcontrol: allow to uncharge page without using page->lru field
>   mm/memcontrol: support MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_PUBLIC
>     v3
>   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 |  25 ++++-
>  include/linux/mm.h       |  20 ++--
>  kernel/memremap.c        |  19 ++--
>  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, 434 insertions(+), 134 deletions(-)
>