From: Michal Hocko <mhocko@kernel.org>
To: "Jérôme Glisse" <jglisse@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
John Hubbard <jhubbard@nvidia.com>,
David Nellans <dnellans@nvidia.com>,
Dan Williams <dan.j.williams@intel.com>,
Balbir Singh <bsingharora@gmail.com>
Subject: Re: [PATCH 6/6] mm/hmm: documents how device memory is accounted in rss and memcg
Date: Fri, 14 Jul 2017 15:26:11 +0200 [thread overview]
Message-ID: <20170714132611.GS2618@dhcp22.suse.cz> (raw)
In-Reply-To: <20170713211532.970-7-jglisse@redhat.com>
On Thu 13-07-17 17:15:32, Jérôme Glisse wrote:
> For now we account device memory exactly like a regular page in
> respect to rss counters and memory cgroup. We do this so that any
> existing application that starts using device memory without knowing
> about it will keep running unimpacted. This also simplify migration
> code.
>
> We will likely revisit this choice once we gain more experience with
> how device memory is use and how it impacts overall memory resource
> management. For now we believe this is a good enough choice.
>
> Note that device memory can not be pin. Nor by device driver, nor
> by GUP thus device memory can always be free and unaccounted when
> a process exit.
I have to look at the implementation but this gives a good idea of what
is going on and why.
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Michal Hocko <mhocko@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> Documentation/vm/hmm.txt | 40 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
>
> diff --git a/Documentation/vm/hmm.txt b/Documentation/vm/hmm.txt
> index 192dcdb38bd1..4d3aac9f4a5d 100644
> --- a/Documentation/vm/hmm.txt
> +++ b/Documentation/vm/hmm.txt
> @@ -15,6 +15,15 @@ section present the new migration helper that allow to leverage the device DMA
> engine.
>
>
> +1) Problems of using device specific memory allocator:
> +2) System bus, device memory characteristics
> +3) Share address space and migration
> +4) Address space mirroring implementation and API
> +5) Represent and manage device memory from core kernel point of view
> +6) Migrate to and from device memory
> +7) Memory cgroup (memcg) and rss accounting
> +
> +
> -------------------------------------------------------------------------------
>
> 1) Problems of using device specific memory allocator:
> @@ -342,3 +351,34 @@ that happens then the finalize_and_map() can catch any pages that was not
> migrated. Note those page were still copied to new page and thus we wasted
> bandwidth but this is considered as a rare event and a price that we are
> willing to pay to keep all the code simpler.
> +
> +
> +-------------------------------------------------------------------------------
> +
> +7) Memory cgroup (memcg) and rss accounting
> +
> +For now device memory is accounted as any regular page in rss counters (either
> +anonymous if device page is use for anonymous, file if device page is use for
> +file back page or shmem if device page is use for share memory). This is a
> +deliberate choice to keep existing application that might start using device
> +memory without knowing about it to keep runing unimpacted.
> +
> +Drawbacks is that OOM killer might kill an application using a lot of device
> +memory and not a lot of regular system memory and thus not freeing much system
> +memory. We want to gather more real world experience on how application and
> +system react under memory pressure in the presence of device memory before
> +deciding to account device memory differently.
> +
> +
> +Same decision was made for memory cgroup. Device memory page are accounted
> +against same memory cgroup a regular page would be accounted to. This does
> +simplify migration to and from device memory. This also means that migration
> +back from device memory to regular memory can not fail because it would
> +go above memory cgroup limit. We might revisit this choice latter on once we
> +get more experience in how device memory is use and its impact on memory
> +resource control.
> +
> +
> +Note that device memory can never be pin nor by device driver nor through GUP
> +and thus such memory is always free upon process exit. Or when last reference
> +is drop in case of share memory or file back memory.
> --
> 2.13.0
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-07-14 13:27 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-13 21:15 [PATCH 0/6] Cache coherent device memory (CDM) with HMM v5 Jérôme Glisse
2017-07-13 21:15 ` [PATCH 1/6] mm/zone-device: rename DEVICE_PUBLIC to DEVICE_HOST Jérôme Glisse
2017-07-17 9:09 ` Balbir Singh
2017-07-13 21:15 ` [PATCH 2/6] mm/device-public-memory: device memory cache coherent with CPU v4 Jérôme Glisse
2017-07-13 23:01 ` Balbir Singh
2017-07-13 21:15 ` [PATCH 3/6] mm/hmm: add new helper to hotplug CDM memory region v3 Jérôme Glisse
2017-07-13 21:15 ` [PATCH 4/6] mm/memcontrol: allow to uncharge page without using page->lru field Jérôme Glisse
2017-07-17 9:10 ` Balbir Singh
2017-07-13 21:15 ` [PATCH 5/6] mm/memcontrol: support MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_PUBLIC v3 Jérôme Glisse
2017-07-17 9:15 ` Balbir Singh
2017-07-13 21:15 ` [PATCH 6/6] mm/hmm: documents how device memory is accounted in rss and memcg Jérôme Glisse
2017-07-14 13:26 ` Michal Hocko [this message]
2017-07-18 3:26 ` [PATCH 0/6] Cache coherent device memory (CDM) with HMM v5 Bob Liu
2017-07-18 15:38 ` Jerome Glisse
2017-07-19 1:46 ` Bob Liu
2017-07-19 2:25 ` Jerome Glisse
2017-07-19 9:09 ` Bob Liu
2017-07-20 15:03 ` Jerome Glisse
2017-07-21 1:15 ` Bob Liu
2017-07-21 1:41 ` Jerome Glisse
2017-07-21 2:10 ` Bob Liu
2017-07-21 12:01 ` Bob Liu
2017-07-21 15:21 ` Jerome Glisse
2017-07-21 3:48 ` Dan Williams
2017-07-21 15:22 ` Jerome Glisse
2017-09-05 19:36 ` Jerome Glisse
2017-09-09 23:22 ` Bob Liu
2017-09-11 23:36 ` Jerome Glisse
2017-09-12 1:02 ` Bob Liu
2017-09-12 16:17 ` Jerome Glisse
2017-09-26 9:56 ` Bob Liu
2017-09-26 16:16 ` Jerome Glisse
2017-09-30 2:57 ` Bob Liu
2017-09-30 22:49 ` Jerome Glisse
2017-10-11 13:15 ` Bob Liu
2017-10-12 15:37 ` Jerome Glisse
2017-11-16 2:10 ` chet l
2017-11-16 2:44 ` Jerome Glisse
2017-11-16 3:23 ` chetan L
2017-11-16 3:29 ` chetan L
2017-11-16 21:29 ` Jerome Glisse
2017-11-16 22:41 ` chetan L
2017-11-16 23:11 ` Jerome Glisse
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