linux-stable.git/mm/page_alloc.c, branch v5.2

mm/page_alloc.c: fix regression with deferred struct page init

2019-07-05T02:12:07+00:00

Commit 0e56acae4b4d ("mm: initialize MAX_ORDER_NR_PAGES at a time
instead of doing larger sections") is causing a regression on some
systems when the kernel is booted as Xen dom0.

The system will just hang in early boot.

Reason is an endless loop in get_page_from_freelist() in case the first
zone looked at has no free memory.  deferred_grow_zone() is always
returning true due to the following code snipplet:

  /* If the zone is empty somebody else may have cleared out the zone */
  if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
                                           first_deferred_pfn)) {
          pgdat->first_deferred_pfn = ULONG_MAX;
          pgdat_resize_unlock(pgdat, &flags);
          return true;
  }

This in turn results in the loop as get_page_from_freelist() is assuming
forward progress can be made by doing some more struct page
initialization.

Link: http://lkml.kernel.org/r/20190620160821.4210-1-jgross@suse.com
Fixes: 0e56acae4b4d ("mm: initialize MAX_ORDER_NR_PAGES at a time instead of doing larger sections")
Signed-off-by: Juergen Gross 
Suggested-by: Alexander Duyck 
Acked-by: Alexander Duyck 
Cc: Michal Hocko 
Cc: Pavel Tatashin 
Cc: Mike Rapoport 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

treewide: Add SPDX license identifier for missed files

2019-05-21T08:50:45+00:00

Add SPDX license identifiers to all files which:

 - Have no license information of any form

 - Have EXPORT_.*_SYMBOL_GPL inside which was used in the
   initial scan/conversion to ignore the file

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

mm: maintain randomization of page free lists

2019-05-15T02:52:48+00:00

When freeing a page with an order >= shuffle_page_order randomly select
the front or back of the list for insertion.

While the mm tries to defragment physical pages into huge pages this can
tend to make the page allocator more predictable over time.  Inject the
front-back randomness to preserve the initial randomness established by
shuffle_free_memory() when the kernel was booted.

The overhead of this manipulation is constrained by only being applied
for MAX_ORDER sized pages by default.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/154899812788.3165233.9066631950746578517.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams 
Reviewed-by: Kees Cook 
Cc: Michal Hocko 
Cc: Dave Hansen 
Cc: Keith Busch 
Cc: Robert Elliott 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: move buddy list manipulations into helpers

2019-05-15T02:52:48+00:00

In preparation for runtime randomization of the zone lists, take all
(well, most of) the list_*() functions in the buddy allocator and put
them in helper functions.  Provide a common control point for injecting
additional behavior when freeing pages.

[dan.j.williams@intel.com: fix buddy list helpers]
  Link: http://lkml.kernel.org/r/155033679702.1773410.13041474192173212653.stgit@dwillia2-desk3.amr.corp.intel.com
[vbabka@suse.cz: remove del_page_from_free_area() migratetype parameter]
  Link: http://lkml.kernel.org/r/4672701b-6775-6efd-0797-b6242591419e@suse.cz
Link: http://lkml.kernel.org/r/154899812264.3165233.5219320056406926223.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams 
Signed-off-by: Vlastimil Babka 
Tested-by: Tetsuo Handa 
Acked-by: Michal Hocko 
Cc: Vlastimil Babka 
Cc: Dave Hansen 
Cc: Kees Cook 
Cc: Keith Busch 
Cc: Robert Elliott 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: shuffle initial free memory to improve memory-side-cache utilization

2019-05-15T02:52:48+00:00

Patch series "mm: Randomize free memory", v10.

This patch (of 3):

Randomization of the page allocator improves the average utilization of
a direct-mapped memory-side-cache.  Memory side caching is a platform
capability that Linux has been previously exposed to in HPC
(high-performance computing) environments on specialty platforms.  In
that instance it was a smaller pool of high-bandwidth-memory relative to
higher-capacity / lower-bandwidth DRAM.  Now, this capability is going
to be found on general purpose server platforms where DRAM is a cache in
front of higher latency persistent memory [1].

Robert offered an explanation of the state of the art of Linux
interactions with memory-side-caches [2], and I copy it here:

    It's been a problem in the HPC space:
    http://www.nersc.gov/research-and-development/knl-cache-mode-performance-coe/

    A kernel module called zonesort is available to try to help:
    https://software.intel.com/en-us/articles/xeon-phi-software

    and this abandoned patch series proposed that for the kernel:
    https://lkml.kernel.org/r/20170823100205.17311-1-lukasz.daniluk@intel.com

    Dan's patch series doesn't attempt to ensure buffers won't conflict, but
    also reduces the chance that the buffers will. This will make performance
    more consistent, albeit slower than "optimal" (which is near impossible
    to attain in a general-purpose kernel).  That's better than forcing
    users to deploy remedies like:
        "To eliminate this gradual degradation, we have added a Stream
         measurement to the Node Health Check that follows each job;
         nodes are rebooted whenever their measured memory bandwidth
         falls below 300 GB/s."

A replacement for zonesort was merged upstream in commit cc9aec03e58f
("x86/numa_emulation: Introduce uniform split capability").  With this
numa_emulation capability, memory can be split into cache sized
("near-memory" sized) numa nodes.  A bind operation to such a node, and
disabling workloads on other nodes, enables full cache performance.
However, once the workload exceeds the cache size then cache conflicts
are unavoidable.  While HPC environments might be able to tolerate
time-scheduling of cache sized workloads, for general purpose server
platforms, the oversubscribed cache case will be the common case.

The worst case scenario is that a server system owner benchmarks a
workload at boot with an un-contended cache only to see that performance
degrade over time, even below the average cache performance due to
excessive conflicts.  Randomization clips the peaks and fills in the
valleys of cache utilization to yield steady average performance.

Here are some performance impact details of the patches:

1/ An Intel internal synthetic memory bandwidth measurement tool, saw a
   3X speedup in a contrived case that tries to force cache conflicts.
   The contrived cased used the numa_emulation capability to force an
   instance of the benchmark to be run in two of the near-memory sized
   numa nodes.  If both instances were placed on the same emulated they
   would fit and cause zero conflicts.  While on separate emulated nodes
   without randomization they underutilized the cache and conflicted
   unnecessarily due to the in-order allocation per node.

2/ A well known Java server application benchmark was run with a heap
   size that exceeded cache size by 3X.  The cache conflict rate was 8%
   for the first run and degraded to 21% after page allocator aging.  With
   randomization enabled the rate levelled out at 11%.

3/ A MongoDB workload did not observe measurable difference in
   cache-conflict rates, but the overall throughput dropped by 7% with
   randomization in one case.

4/ Mel Gorman ran his suite of performance workloads with randomization
   enabled on platforms without a memory-side-cache and saw a mix of some
   improvements and some losses [3].

While there is potentially significant improvement for applications that
depend on low latency access across a wide working-set, the performance
may be negligible to negative for other workloads.  For this reason the
shuffle capability defaults to off unless a direct-mapped
memory-side-cache is detected.  Even then, the page_alloc.shuffle=0
parameter can be specified to disable the randomization on those systems.

Outside of memory-side-cache utilization concerns there is potentially
security benefit from randomization.  Some data exfiltration and
return-oriented-programming attacks rely on the ability to infer the
location of sensitive data objects.  The kernel page allocator, especially
early in system boot, has predictable first-in-first out behavior for
physical pages.  Pages are freed in physical address order when first
onlined.

Quoting Kees:
    "While we already have a base-address randomization
     (CONFIG_RANDOMIZE_MEMORY), attacks against the same hardware and
     memory layouts would certainly be using the predictability of
     allocation ordering (i.e. for attacks where the base address isn't
     important: only the relative positions between allocated memory).
     This is common in lots of heap-style attacks. They try to gain
     control over ordering by spraying allocations, etc.

     I'd really like to see this because it gives us something similar
     to CONFIG_SLAB_FREELIST_RANDOM but for the page allocator."

While SLAB_FREELIST_RANDOM reduces the predictability of some local slab
caches it leaves vast bulk of memory to be predictably in order allocated.
However, it should be noted, the concrete security benefits are hard to
quantify, and no known CVE is mitigated by this randomization.

Introduce shuffle_free_memory(), and its helper shuffle_zone(), to perform
a Fisher-Yates shuffle of the page allocator 'free_area' lists when they
are initially populated with free memory at boot and at hotplug time.  Do
this based on either the presence of a page_alloc.shuffle=Y command line
parameter, or autodetection of a memory-side-cache (to be added in a
follow-on patch).

The shuffling is done in terms of CONFIG_SHUFFLE_PAGE_ORDER sized free
pages where the default CONFIG_SHUFFLE_PAGE_ORDER is MAX_ORDER-1 i.e.  10,
4MB this trades off randomization granularity for time spent shuffling.
MAX_ORDER-1 was chosen to be minimally invasive to the page allocator
while still showing memory-side cache behavior improvements, and the
expectation that the security implications of finer granularity
randomization is mitigated by CONFIG_SLAB_FREELIST_RANDOM.  The
performance impact of the shuffling appears to be in the noise compared to
other memory initialization work.

This initial randomization can be undone over time so a follow-on patch is
introduced to inject entropy on page free decisions.  It is reasonable to
ask if the page free entropy is sufficient, but it is not enough due to
the in-order initial freeing of pages.  At the start of that process
putting page1 in front or behind page0 still keeps them close together,
page2 is still near page1 and has a high chance of being adjacent.  As
more pages are added ordering diversity improves, but there is still high
page locality for the low address pages and this leads to no significant
impact to the cache conflict rate.

[1]: https://itpeernetwork.intel.com/intel-optane-dc-persistent-memory-operating-modes/
[2]: https://lkml.kernel.org/r/AT5PR8401MB1169D656C8B5E121752FC0F8AB120@AT5PR8401MB1169.NAMPRD84.PROD.OUTLOOK.COM
[3]: https://lkml.org/lkml/2018/10/12/309

[dan.j.williams@intel.com: fix shuffle enable]
  Link: http://lkml.kernel.org/r/154943713038.3858443.4125180191382062871.stgit@dwillia2-desk3.amr.corp.intel.com
[cai@lca.pw: fix SHUFFLE_PAGE_ALLOCATOR help texts]
  Link: http://lkml.kernel.org/r/20190425201300.75650-1-cai@lca.pw
Link: http://lkml.kernel.org/r/154899811738.3165233.12325692939590944259.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams 
Signed-off-by: Qian Cai 
Reviewed-by: Kees Cook 
Acked-by: Michal Hocko 
Cc: Dave Hansen 
Cc: Keith Busch 
Cc: Robert Elliott 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: update references to page _refcount

2019-05-15T02:52:47+00:00

Commit 0139aa7b7fa ("mm: rename _count, field of the struct page, to
_refcount") left out a couple of references to the old field name.  Fix
that.

Link: http://lkml.kernel.org/r/cedf87b02eb8a6b3eac57e8e91da53fb15c3c44c.1556537475.git.baruch@tkos.co.il
Fixes: 0139aa7b7fa ("mm: rename _count, field of the struct page, to _refcount")
Signed-off-by: Baruch Siach 
Reviewed-by: Andrew Morton 
Cc: Joonsoo Kim 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: memblock: make keeping memblock memory opt-in rather than opt-out

2019-05-14T16:47:50+00:00

Most architectures do not need the memblock memory after the page
allocator is initialized, but only few enable ARCH_DISCARD_MEMBLOCK in the
arch Kconfig.

Replacing ARCH_DISCARD_MEMBLOCK with ARCH_KEEP_MEMBLOCK and inverting the
logic makes it clear which architectures actually use memblock after
system initialization and skips the necessity to add ARCH_DISCARD_MEMBLOCK
to the architectures that are still missing that option.

Link: http://lkml.kernel.org/r/1556102150-32517-1-git-send-email-rppt@linux.ibm.com
Signed-off-by: Mike Rapoport 
Acked-by: Michael Ellerman  (powerpc)
Cc: Russell King 
Cc: Catalin Marinas 
Cc: Will Deacon 
Cc: Richard Kuo 
Cc: Tony Luck 
Cc: Fenghua Yu 
Cc: Geert Uytterhoeven 
Cc: Ralf Baechle 
Cc: Paul Burton 
Cc: James Hogan 
Cc: Ley Foon Tan 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Martin Schwidefsky 
Cc: Heiko Carstens 
Cc: Yoshinori Sato 
Cc: Rich Felker 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Borislav Petkov 
Cc: "H. Peter Anvin" 
Cc: Eric Biederman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/page_alloc.c: remove unnecessary parameter in rmqueue_pcplist

2019-05-14T16:47:50+00:00

Because rmqueue_pcplist() is only called when order is 0, we don't need to
use order as a parameter.

Link: http://lkml.kernel.org/r/1555591709-11744-1-git-send-email-laoar.shao@gmail.com
Signed-off-by: Yafang Shao 
Acked-by: Michal Hocko 
Acked-by: Pankaj Gupta 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, memory_hotplug: cleanup memory offline path

2019-05-14T16:47:49+00:00

check_pages_isolated_cb currently accounts the whole pfn range as being
offlined if test_pages_isolated suceeds on the range.  This is based on
the assumption that all pages in the range are freed which is currently
the case in most cases but it won't be with later changes, as pages marked
as vmemmap won't be isolated.

Move the offlined pages counting to offline_isolated_pages_cb and rely on
__offline_isolated_pages to return the correct value.
check_pages_isolated_cb will still do it's primary job and check the pfn
range.

While we are at it remove check_pages_isolated and offline_isolated_pages
and use directly walk_system_ram_range as do in online_pages.

Link: http://lkml.kernel.org/r/20190408082633.2864-2-osalvador@suse.de
Reviewed-by: David Hildenbrand 
Signed-off-by: Michal Hocko 
Signed-off-by: Oscar Salvador 
Cc: Dan Williams 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: initialize MAX_ORDER_NR_PAGES at a time instead of doing larger sections

2019-05-14T16:47:49+00:00

Add yet another iterator, for_each_free_mem_range_in_zone_from, and then
use it to support initializing and freeing pages in groups no larger than
MAX_ORDER_NR_PAGES.  By doing this we can greatly improve the cache
locality of the pages while we do several loops over them in the init and
freeing process.

We are able to tighten the loops further as a result of the "from"
iterator as we can perform the initial checks for first_init_pfn in our
first call to the iterator, and continue without the need for those checks
via the "from" iterator.  I have added this functionality in the function
called deferred_init_mem_pfn_range_in_zone that primes the iterator and
causes us to exit if we encounter any failure.

On my x86_64 test system with 384GB of memory per node I saw a reduction
in initialization time from 1.85s to 1.38s as a result of this patch.

Link: http://lkml.kernel.org/r/20190405221231.12227.85836.stgit@localhost.localdomain
Signed-off-by: Alexander Duyck 
Reviewed-by: Pavel Tatashin 
Cc: Mike Rapoport 
Cc: Michal Hocko 
Cc: Dave Jiang 
Cc: Matthew Wilcox 
Cc: Ingo Molnar 
Cc: 
Cc: Khalid Aziz 
Cc: Mike Rapoport 
Cc: Vlastimil Babka 
Cc: Dan Williams 
Cc: Laurent Dufour 
Cc: Mel Gorman 
Cc: David S. Miller 
Cc: "Kirill A. Shutemov" 
Cc: Pavel Tatashin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds