linux-toradex.git/include/linux/memory_hotplug.h, branch v6.0-rc1

mm: memory_hotplug: make hugetlb_optimize_vmemmap compatible with memmap_on_memory

2022-07-04T01:08:49+00:00

For now, the feature of hugetlb_free_vmemmap is not compatible with the
feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap takes
precedence over memory_hotplug.memmap_on_memory.  However, someone wants
to make memory_hotplug.memmap_on_memory takes precedence over
hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
succeed memory hotplug in close-to-OOM situations.  So the decision of
making hugetlb_free_vmemmap take precedence is not wise and elegant.

The proper approach is to have hugetlb_vmemmap.c do the check whether the
section which the HugeTLB pages belong to can be optimized.  If the
section's vmemmap pages are allocated from the added memory block itself,
hugetlb_free_vmemmap should refuse to optimize the vmemmap, otherwise, do
the optimization.  Then both kernel parameters are compatible.  So this
patch introduces VmemmapSelfHosted to mask any non-optimizable vmemmap
pages.  The hugetlb_vmemmap can use this flag to detect if a vmemmap page
can be optimized.

[songmuchun@bytedance.com: walk vmemmap page tables to avoid false-positive]
  Link: https://lkml.kernel.org/r/20220620110616.12056-3-songmuchun@bytedance.com
Link: https://lkml.kernel.org/r/20220617135650.74901-3-songmuchun@bytedance.com
Signed-off-by: Muchun Song 
Co-developed-by: Oscar Salvador 
Signed-off-by: Oscar Salvador 
Acked-by: David Hildenbrand 
Cc: Jonathan Corbet 
Cc: Mike Kravetz 
Cc: Paul E. McKenney 
Cc: Xiongchun Duan 
Signed-off-by: Andrew Morton

mm: hugetlb_vmemmap: add hugetlb_optimize_vmemmap sysctl

2022-05-13T23:48:56+00:00

We must add hugetlb_free_vmemmap=on (or "off") to the boot cmdline and
reboot the server to enable or disable the feature of optimizing vmemmap
pages associated with HugeTLB pages.  However, rebooting usually takes a
long time.  So add a sysctl to enable or disable the feature at runtime
without rebooting.  Why we need this?  There are 3 use cases.

1) The feature of minimizing overhead of struct page associated with
   each HugeTLB is disabled by default without passing
   "hugetlb_free_vmemmap=on" to the boot cmdline.  When we (ByteDance)
   deliver the servers to the users who want to enable this feature, they
   have to configure the grub (change boot cmdline) and reboot the
   servers, whereas rebooting usually takes a long time (we have thousands
   of servers).  It's a very bad experience for the users.  So we need a
   approach to enable this feature after rebooting.  This is a use case in
   our practical environment.

2) Some use cases are that HugeTLB pages are allocated 'on the fly'
   instead of being pulled from the HugeTLB pool, those workloads would be
   affected with this feature enabled.  Those workloads could be
   identified by the characteristics of they never explicitly allocating
   huge pages with 'nr_hugepages' but only set 'nr_overcommit_hugepages'
   and then let the pages be allocated from the buddy allocator at fault
   time.  We can confirm it is a real use case from the commit
   099730d67417.  For those workloads, the page fault time could be ~2x
   slower than before.  We suspect those users want to disable this
   feature if the system has enabled this before and they don't think the
   memory savings benefit is enough to make up for the performance drop.

3) If the workload which wants vmemmap pages to be optimized and the
   workload which wants to set 'nr_overcommit_hugepages' and does not want
   the extera overhead at fault time when the overcommitted pages be
   allocated from the buddy allocator are deployed in the same server. 
   The user could enable this feature and set 'nr_hugepages' and
   'nr_overcommit_hugepages', then disable the feature.  In this case, the
   overcommited HugeTLB pages will not encounter the extra overhead at
   fault time.

Link: https://lkml.kernel.org/r/20220512041142.39501-5-songmuchun@bytedance.com
Signed-off-by: Muchun Song 
Reviewed-by: Mike Kravetz 
Cc: Jonathan Corbet 
Cc: Luis Chamberlain 
Cc: Kees Cook 
Cc: Iurii Zaikin 
Cc: Oscar Salvador 
Cc: David Hildenbrand 
Cc: Masahiro Yamada 
Cc: Xiongchun Duan 
Signed-off-by: Andrew Morton

mm/sparse-vmemmap: add a pgmap argument to section activation

2022-04-29T06:16:15+00:00

Patch series "sparse-vmemmap: memory savings for compound devmaps (device-dax)", v9.

This series minimizes 'struct page' overhead by pursuing a similar
approach as Muchun Song series "Free some vmemmap pages of hugetlb page"
(now merged since v5.14), but applied to devmap with @vmemmap_shift
(device-dax).  

The vmemmap dedpulication original idea (already used in HugeTLB) is to
reuse/deduplicate tail page vmemmap areas, particular the area which only
describes tail pages.  So a vmemmap page describes 64 struct pages, and
the first page for a given ZONE_DEVICE vmemmap would contain the head page
and 63 tail pages.  The second vmemmap page would contain only tail pages,
and that's what gets reused across the rest of the subsection/section. 
The bigger the page size, the bigger the savings (2M hpage -> save 6
vmemmap pages; 1G hpage -> save 4094 vmemmap pages).  

This is done for PMEM /specifically only/ on device-dax configured
namespaces, not fsdax.  In other words, a devmap with a @vmemmap_shift.

In terms of savings, per 1Tb of memory, the struct page cost would go down
with compound devmap:

* with 2M pages we lose 4G instead of 16G (0.39% instead of 1.5% of
  total memory)

* with 1G pages we lose 40MB instead of 16G (0.0014% instead of 1.5% of
  total memory)

The series is mostly summed up by patch 4, and to summarize what the
series does:

Patches 1 - 3: Minor cleanups in preparation for patch 4.  Move the very
nice docs of hugetlb_vmemmap.c into a Documentation/vm/ entry.

Patch 4: Patch 4 is the one that takes care of the struct page savings
(also referred to here as tail-page/vmemmap deduplication).  Much like
Muchun series, we reuse the second PTE tail page vmemmap areas across a
given @vmemmap_shift On important difference though, is that contrary to
the hugetlbfs series, there's no vmemmap for the area because we are
late-populating it as opposed to remapping a system-ram range.  IOW no
freeing of pages of already initialized vmemmap like the case for
hugetlbfs, which greatly simplifies the logic (besides not being
arch-specific).  altmap case unchanged and still goes via the
vmemmap_populate().  Also adjust the newly added docs to the device-dax
case.

[Note that device-dax is still a little behind HugeTLB in terms of
savings.  I have an additional simple patch that reuses the head vmemmap
page too, as a follow-up.  That will double the savings and namespaces
initialization.]

Patch 5: Initialize fewer struct pages depending on the page size with
DRAM backed struct pages -- because fewer pages are unique and most tail
pages (with bigger vmemmap_shift).

    NVDIMM namespace bootstrap improves from ~268-358 ms to
    ~80-110/<1ms on 128G NVDIMMs with 2M and 1G respectivally.  And struct
    page needed capacity will be 3.8x / 1071x smaller for 2M and 1G
    respectivelly.  Tested on x86 with 1.5Tb of pmem (including pinning,
    and RDMA registration/deregistration scalability with 2M MRs)


This patch (of 5):

In support of using compound pages for devmap mappings, plumb the pgmap
down to the vmemmap_populate implementation.  Note that while altmap is
retrievable from pgmap the memory hotplug code passes altmap without
pgmap[*], so both need to be independently plumbed.

So in addition to @altmap, pass @pgmap to sparse section populate
functions namely:

	sparse_add_section
	  section_activate
	    populate_section_memmap
   	      __populate_section_memmap

Passing @pgmap allows __populate_section_memmap() to both fetch the
vmemmap_shift in which memmap metadata is created for and also to let
sparse-vmemmap fetch pgmap ranges to co-relate to a given section and pick
whether to just reuse tail pages from past onlined sections.

While at it, fix the kdoc for @altmap for sparse_add_section().

[*] https://lore.kernel.org/linux-mm/20210319092635.6214-1-osalvador@suse.de/

Link: https://lkml.kernel.org/r/20220420155310.9712-1-joao.m.martins@oracle.com
Link: https://lkml.kernel.org/r/20220420155310.9712-2-joao.m.martins@oracle.com
Signed-off-by: Joao Martins 
Reviewed-by: Dan Williams 
Reviewed-by: Muchun Song 
Cc: Vishal Verma 
Cc: Matthew Wilcox 
Cc: Jason Gunthorpe 
Cc: Jane Chu 
Cc: Mike Kravetz 
Cc: Jonathan Corbet 
Cc: Christoph Hellwig 
Signed-off-by: Andrew Morton

drivers/base/memory: determine and store zone for single-zone memory blocks

2022-03-22T22:57:10+00:00

test_pages_in_a_zone() is just another nasty PFN walker that can easily
stumble over ZONE_DEVICE memory ranges falling into the same memory block
as ordinary system RAM: the memmap of parts of these ranges might possibly
be uninitialized.  In fact, we observed (on an older kernel) with UBSAN:

  UBSAN: Undefined behaviour in ./include/linux/mm.h:1133:50
  index 7 is out of range for type 'zone [5]'
  CPU: 121 PID: 35603 Comm: read_all Kdump: loaded Tainted: [...]
  Hardware name: Dell Inc. PowerEdge R7425/08V001, BIOS 1.12.2 11/15/2019
  Call Trace:
   dump_stack+0x9a/0xf0
   ubsan_epilogue+0x9/0x7a
   __ubsan_handle_out_of_bounds+0x13a/0x181
   test_pages_in_a_zone+0x3c4/0x500
   show_valid_zones+0x1fa/0x380
   dev_attr_show+0x43/0xb0
   sysfs_kf_seq_show+0x1c5/0x440
   seq_read+0x49d/0x1190
   vfs_read+0xff/0x300
   ksys_read+0xb8/0x170
   do_syscall_64+0xa5/0x4b0
   entry_SYSCALL_64_after_hwframe+0x6a/0xdf
  RIP: 0033:0x7f01f4439b52

We seem to stumble over a memmap that contains a garbage zone id.  While
we could try inserting pfn_to_online_page() calls, it will just make
memory offlining slower, because we use test_pages_in_a_zone() to make
sure we're offlining pages that all belong to the same zone.

Let's just get rid of this PFN walker and determine the single zone of a
memory block -- if any -- for early memory blocks during boot.  For memory
onlining, we know the single zone already.  Let's avoid any additional
memmap scanning and just rely on the zone information available during
boot.

For memory hot(un)plug, we only really care about memory blocks that:
* span a single zone (and, thereby, a single node)
* are completely System RAM (IOW, no holes, no ZONE_DEVICE)
If one of these conditions is not met, we reject memory offlining.
Hotplugged memory blocks (starting out offline), always meet both
conditions.

There are three scenarios to handle:

(1) Memory hot(un)plug

A memory block with zone == NULL cannot be offlined, corresponding to
our previous test_pages_in_a_zone() check.

After successful memory onlining/offlining, we simply set the zone
accordingly.
* Memory onlining: set the zone we just used for onlining
* Memory offlining: set zone = NULL

So a hotplugged memory block starts with zone = NULL. Once memory
onlining is done, we set the proper zone.

(2) Boot memory with !CONFIG_NUMA

We know that there is just a single pgdat, so we simply scan all zones
of that pgdat for an intersection with our memory block PFN range when
adding the memory block. If more than one zone intersects (e.g., DMA and
DMA32 on x86 for the first memory block) we set zone = NULL and
consequently mimic what test_pages_in_a_zone() used to do.

(3) Boot memory with CONFIG_NUMA

At the point in time we create the memory block devices during boot, we
don't know yet which nodes *actually* span a memory block. While we could
scan all zones of all nodes for intersections, overlapping nodes complicate
the situation and scanning all nodes is possibly expensive. But that
problem has already been solved by the code that sets the node of a memory
block and creates the link in the sysfs --
do_register_memory_block_under_node().

So, we hook into the code that sets the node id for a memory block. If
we already have a different node id set for the memory block, we know
that multiple nodes *actually* have PFNs falling into our memory block:
we set zone = NULL and consequently mimic what test_pages_in_a_zone() used
to do. If there is no node id set, we do the same as (2) for the given
node.

Note that the call order in driver_init() is:
-> memory_dev_init(): create memory block devices
-> node_dev_init(): link memory block devices to the node and set the
		    node id

So in summary, we detect if there is a single zone responsible for this
memory block and we consequently store the zone in that case in the
memory block, updating it during memory onlining/offlining.

Link: https://lkml.kernel.org/r/20220210184359.235565-3-david@redhat.com
Signed-off-by: David Hildenbrand 
Reported-by: Rafael Parra 
Reviewed-by: Oscar Salvador 
Cc: "Rafael J. Wysocki" 
Cc: Greg Kroah-Hartman 
Cc: Michal Hocko 
Cc: Rafael Parra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, memory_hotplug: reorganize new pgdat initialization

2022-03-22T22:57:10+00:00

When a !node_online node is brought up it needs a hotplug specific
initialization because the node could be either uninitialized yet or it
could have been recycled after previous hotremove.  hotadd_init_pgdat is
responsible for that.

Internal pgdat state is initialized at two places currently
	- hotadd_init_pgdat
	- free_area_init_core_hotplug

There is no real clear cut what should go where but this patch's chosen to
move the whole internal state initialization into
free_area_init_core_hotplug.  hotadd_init_pgdat is still responsible to
pull all the parts together - most notably to initialize zonelists because
those depend on the overall topology.

This patch doesn't introduce any functional change.

Link: https://lkml.kernel.org/r/20220127085305.20890-5-mhocko@kernel.org
Signed-off-by: Michal Hocko 
Acked-by: Rafael Aquini 
Acked-by: David Hildenbrand 
Reviewed-by: Oscar Salvador 
Cc: Alexey Makhalov 
Cc: Christoph Lameter 
Cc: Dennis Zhou 
Cc: Eric Dumazet 
Cc: Mike Rapoport 
Cc: Nico Pache 
Cc: Tejun Heo 
Cc: Wei Yang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, memory_hotplug: drop arch_free_nodedata

2022-03-22T22:57:10+00:00

Prior to "mm: handle uninitialized numa nodes gracefully" memory hotplug
used to allocate pgdat when memory has been added to a node
(hotadd_init_pgdat) arch_free_nodedata has been only used in the failure
path because once the pgdat is exported (to be visible by NODA_DATA(nid))
it cannot really be freed because there is no synchronization available
for that.

pgdat is allocated for each possible nodes now so the memory hotplug
doesn't need to do the ever use arch_free_nodedata so drop it.

This patch doesn't introduce any functional change.

Link: https://lkml.kernel.org/r/20220127085305.20890-4-mhocko@kernel.org
Signed-off-by: Michal Hocko 
Acked-by: Rafael Aquini 
Acked-by: David Hildenbrand 
Acked-by: Mike Rapoport 
Reviewed-by: Oscar Salvador 
Cc: Alexey Makhalov 
Cc: Christoph Lameter 
Cc: Dennis Zhou 
Cc: Eric Dumazet 
Cc: Nico Pache 
Cc: Tejun Heo 
Cc: Wei Yang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: handle uninitialized numa nodes gracefully

2022-03-22T22:57:10+00:00

We have had several reports [1][2][3] that page allocator blows up when an
allocation from a possible node is requested.  The underlying reason is
that NODE_DATA for the specific node is not allocated.

NUMA specific initialization is arch specific and it can vary a lot.  E.g.
x86 tries to initialize all nodes that have some cpu affinity (see
init_cpu_to_node) but this can be insufficient because the node might be
cpuless for example.

One way to address this problem would be to check for !node_online nodes
when trying to get a zonelist and silently fall back to another node.
That is unfortunately adding a branch into allocator hot path and it
doesn't handle any other potential NODE_DATA users.

This patch takes a different approach (following a lead of [3]) and it pre
allocates pgdat for all possible nodes in an arch indipendent code -
free_area_init.  All uninitialized nodes are treated as memoryless nodes.
node_state of the node is not changed because that would lead to other
side effects - e.g.  sysfs representation of such a node and from past
discussions [4] it is known that some tools might have problems digesting
that.

Newly allocated pgdat only gets a minimal initialization and the rest of
the work is expected to be done by the memory hotplug - hotadd_new_pgdat
(renamed to hotadd_init_pgdat).

generic_alloc_nodedata is changed to use the memblock allocator because
neither page nor slab allocators are available at the stage when all
pgdats are allocated.  Hotplug doesn't allocate pgdat anymore so we can
use the early boot allocator.  The only arch specific implementation is
ia64 and that is changed to use the early allocator as well.

[1] http://lkml.kernel.org/r/20211101201312.11589-1-amakhalov@vmware.com
[2] http://lkml.kernel.org/r/20211207224013.880775-1-npache@redhat.com
[3] http://lkml.kernel.org/r/20190114082416.30939-1-mhocko@kernel.org
[4] http://lkml.kernel.org/r/20200428093836.27190-1-srikar@linux.vnet.ibm.com

[akpm@linux-foundation.org: replace comment, per Mike]

Link: https://lkml.kernel.org/r/Yfe7RBeLCijnWBON@dhcp22.suse.cz
Reported-by: Alexey Makhalov 
Tested-by: Alexey Makhalov 
Reported-by: Nico Pache 
Acked-by: Rafael Aquini 
Tested-by: Rafael Aquini 
Acked-by: David Hildenbrand 
Reviewed-by: Oscar Salvador 
Acked-by: Mike Rapoport 
Signed-off-by: Michal Hocko 
Cc: Christoph Lameter 
Cc: Dennis Zhou 
Cc: Eric Dumazet 
Cc: Tejun Heo 
Cc: Wei Yang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, memory_hotplug: make arch_alloc_nodedata independent on CONFIG_MEMORY_HOTPLUG

2022-03-22T22:57:10+00:00

Patch series "mm, memory_hotplug: handle unitialized numa node gracefully".

The core of the fix is patch 2 which also links existing bug reports.  The
high level goal is to have all possible numa nodes have their pgdat
allocated and initialized so

	for_each_possible_node(nid)
		NODE_DATA(nid)

will never return garbage.  This has proven to be problem in several
places when an offline numa node is used for an allocation just to realize
that node_data and therefore allocation fallback zonelists are not
initialized and such an allocation request blows up.

There were attempts to address that by checking node_online in several
places including the page allocator.  This patchset approaches the problem
from a different perspective and instead of special casing, which just
adds a runtime overhead, it allocates pglist_data for each possible node.
This can add some memory overhead for platforms with high number of
possible nodes if they do not contain any memory.  This should be a rather
rare configuration though.

How to test this? David has provided and excellent howto:
http://lkml.kernel.org/r/6e5ebc19-890c-b6dd-1924-9f25c441010d@redhat.com

Patches 1 and 3-6 are mostly cleanups.  The patchset has been reviewed by
Rafael (thanks!) and the core fix tested by Rafael and Alexey (thanks to
both).  David has tested as per instructions above and hasn't found any
fallouts in the memory hotplug scenarios.

This patch (of 6):

This is a preparatory patch and it doesn't introduce any functional
change.  It merely pulls out arch_alloc_nodedata (and co) outside of
CONFIG_MEMORY_HOTPLUG because the following patch will need to call this
from the generic MM code.

Link: https://lkml.kernel.org/r/20220127085305.20890-1-mhocko@kernel.org
Link: https://lkml.kernel.org/r/20220127085305.20890-2-mhocko@kernel.org
Signed-off-by: Michal Hocko 
Acked-by: Rafael Aquini 
Acked-by: David Hildenbrand 
Acked-by: Mike Rapoport 
Reviewed-by: Oscar Salvador 
Reviewed-by: Wei Yang 
Cc: Alexey Makhalov 
Cc: Christoph Lameter 
Cc: Dennis Zhou 
Cc: Eric Dumazet 
Cc: Nico Pache 
Cc: Tejun Heo 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/memory_hotplug: remove stale function declarations

2021-11-06T20:30:42+00:00

These functions no longer exist.

Link: https://lkml.kernel.org/r/20210929143600.49379-6-david@redhat.com
Signed-off-by: David Hildenbrand 
Reviewed-by: Oscar Salvador 
Cc: Alex Shi 
Cc: Andy Lutomirski 
Cc: Benjamin Herrenschmidt 
Cc: Borislav Petkov 
Cc: Dave Hansen 
Cc: Greg Kroah-Hartman 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jason Wang 
Cc: Jonathan Corbet 
Cc: Michael Ellerman 
Cc: "Michael S. Tsirkin" 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Paul Mackerras 
Cc: Peter Zijlstra 
Cc: "Rafael J. Wysocki" 
Cc: Shuah Khan 
Cc: Thomas Gleixner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/memory_hotplug: memory group aware "auto-movable" online policy

2021-09-08T18:50:23+00:00

Use memory groups to improve our "auto-movable" onlining policy:

1. For static memory groups (e.g., a DIMM), online a memory block MOVABLE
   only if all other memory blocks in the group are either MOVABLE or could
   be onlined MOVABLE. A DIMM will either be MOVABLE or not, not a mixture.

2. For dynamic memory groups (e.g., a virtio-mem device), online a
   memory block MOVABLE only if all other memory blocks inside the
   current unit are either MOVABLE or could be onlined MOVABLE. For a
   virtio-mem device with a device block size with 512 MiB, all 128 MiB
   memory blocks wihin a 512 MiB unit will either be MOVABLE or not, not
   a mixture.

We have to pass the memory group to zone_for_pfn_range() to take the
memory group into account.

Note: for now, there seems to be no compelling reason to make this
behavior configurable.

Link: https://lkml.kernel.org/r/20210806124715.17090-9-david@redhat.com
Signed-off-by: David Hildenbrand 
Cc: Anshuman Khandual 
Cc: Dan Williams 
Cc: Dave Hansen 
Cc: Greg Kroah-Hartman 
Cc: Hui Zhu 
Cc: Jason Wang 
Cc: Len Brown 
Cc: Marek Kedzierski 
Cc: "Michael S. Tsirkin" 
Cc: Michal Hocko 
Cc: Mike Rapoport 
Cc: Oscar Salvador 
Cc: Pankaj Gupta 
Cc: Pavel Tatashin 
Cc: Rafael J. Wysocki 
Cc: "Rafael J. Wysocki" 
Cc: Vitaly Kuznetsov 
Cc: Vlastimil Babka 
Cc: Wei Yang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds