Re: [PATCH v1 0/4]mm: convert totalram_pages, totalhigh_pages and managed pages to atomic

[Konstantin Khlebnikov <khlebnikov@yandex-team.ru>]

On 06.11.2018 11:43, Arun KS wrote:
> On 2018-11-06 14:07, Konstantin Khlebnikov wrote:
>> On 06.11.2018 11:30, Arun KS wrote:
>>> On 2018-11-06 13:47, Konstantin Khlebnikov wrote:
>>>> On 06.11.2018 8:38, Arun KS wrote:
>>>>> Any comments?
>>>>
>>>> Looks good.
>>>> Except unclear motivation behind this change.
>>>> This should be in comment of one of patch.
>>>
>>> totalram_pages, zone->managed_pages and totalhigh_pages are sometimes modified outside managed_page_count_lock. Hence convert these 
>>> variable to atomic to avoid readers potentially seeing a store tear.
>>
>> So, this is just theoretical issue or splat from sanitizer.
>> After boot memory online\offline are strictly serialized by rw-semaphore.
> 
> Few instances which can race with hot add. Please see below,
> https://patchwork.kernel.org/patch/10627521/
Could you point what exactly are you fixing with this set?

from v2:

 > totalram_pages, zone->managed_pages and totalhigh_pages updates
 > are protected by managed_page_count_lock, but readers never care
 > about it. Convert these variables to atomic to avoid readers
 > potentially seeing a store tear.

This?


Aligned unsigned long almost always stored at once.

To make it completely correct you could replace

a += b;

with

WRITE_ONCE(a, a + b);

> 
> Regards,
> Arun
> 
>>
>>>
>>> Will update the comment.
>>>
>>> Regards,
>>> Arun
>>>
>>>>
>>>> Reviewed-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>>>>
>>>>>
>>>>> Regards,
>>>>> Arun
>>>>>
>>>>> On 2018-10-26 16:30, Arun KS wrote:
>>>>>> This series convert totalram_pages, totalhigh_pages and
>>>>>> zone->managed_pages to atomic variables.
>>>>>>
>>>>>> The patch was comiple tested on x86(x86_64_defconfig & i386_defconfig)
>>>>>> on tip of linux-mmotm. And memory hotplug tested on arm64, but on an
>>>>>> older version of kernel.
>>>>>>
>>>>>> Arun KS (4):
>>>>>>   mm: Fix multiple evaluvations of totalram_pages and managed_pages
>>>>>>   mm: Convert zone->managed_pages to atomic variable
>>>>>>   mm: convert totalram_pages and totalhigh_pages variables to atomic
>>>>>>   mm: Remove managed_page_count spinlock
>>>>>>
>>>>>>  arch/csky/mm/init.c                           |  4 +-
>>>>>>  arch/powerpc/platforms/pseries/cmm.c          | 10 ++--
>>>>>>  arch/s390/mm/init.c                           |  2 +-
>>>>>>  arch/um/kernel/mem.c                          |  3 +-
>>>>>>  arch/x86/kernel/cpu/microcode/core.c          |  5 +-
>>>>>>  drivers/char/agp/backend.c                    |  4 +-
>>>>>>  drivers/gpu/drm/amd/amdkfd/kfd_crat.c         |  2 +-
>>>>>>  drivers/gpu/drm/i915/i915_gem.c               |  2 +-
>>>>>>  drivers/gpu/drm/i915/selftests/i915_gem_gtt.c |  4 +-
>>>>>>  drivers/hv/hv_balloon.c                       | 19 +++----
>>>>>>  drivers/md/dm-bufio.c                         |  2 +-
>>>>>>  drivers/md/dm-crypt.c                         |  2 +-
>>>>>>  drivers/md/dm-integrity.c                     |  2 +-
>>>>>>  drivers/md/dm-stats.c                         |  2 +-
>>>>>>  drivers/media/platform/mtk-vpu/mtk_vpu.c      |  2 +-
>>>>>>  drivers/misc/vmw_balloon.c                    |  2 +-
>>>>>>  drivers/parisc/ccio-dma.c                     |  4 +-
>>>>>>  drivers/parisc/sba_iommu.c                    |  4 +-
>>>>>>  drivers/staging/android/ion/ion_system_heap.c |  2 +-
>>>>>>  drivers/xen/xen-selfballoon.c                 |  6 +--
>>>>>>  fs/ceph/super.h                               |  2 +-
>>>>>>  fs/file_table.c                               |  7 +--
>>>>>>  fs/fuse/inode.c                               |  2 +-
>>>>>>  fs/nfs/write.c                                |  2 +-
>>>>>>  fs/nfsd/nfscache.c                            |  2 +-
>>>>>>  fs/ntfs/malloc.h                              |  2 +-
>>>>>>  fs/proc/base.c                                |  2 +-
>>>>>>  include/linux/highmem.h                       | 28 ++++++++++-
>>>>>>  include/linux/mm.h                            | 27 +++++++++-
>>>>>>  include/linux/mmzone.h                        | 15 +++---
>>>>>>  include/linux/swap.h                          |  1 -
>>>>>>  kernel/fork.c                                 |  5 +-
>>>>>>  kernel/kexec_core.c                           |  5 +-
>>>>>>  kernel/power/snapshot.c                       |  2 +-
>>>>>>  lib/show_mem.c                                |  2 +-
>>>>>>  mm/highmem.c                                  |  4 +-
>>>>>>  mm/huge_memory.c                              |  2 +-
>>>>>>  mm/kasan/quarantine.c                         |  2 +-
>>>>>>  mm/memblock.c                                 |  6 +--
>>>>>>  mm/memory_hotplug.c                           |  4 +-
>>>>>>  mm/mm_init.c                                  |  2 +-
>>>>>>  mm/oom_kill.c                                 |  2 +-
>>>>>>  mm/page_alloc.c                               | 71 +++++++++++++--------------
>>>>>>  mm/shmem.c                                    |  7 +--
>>>>>>  mm/slab.c                                     |  2 +-
>>>>>>  mm/swap.c                                     |  2 +-
>>>>>>  mm/util.c                                     |  2 +-
>>>>>>  mm/vmalloc.c                                  |  4 +-
>>>>>>  mm/vmstat.c                                   |  4 +-
>>>>>>  mm/workingset.c                               |  2 +-
>>>>>>  mm/zswap.c                                    |  4 +-
>>>>>>  net/dccp/proto.c                              |  7 +--
>>>>>>  net/decnet/dn_route.c                         |  2 +-
>>>>>>  net/ipv4/tcp_metrics.c                        |  2 +-
>>>>>>  net/netfilter/nf_conntrack_core.c             |  7 +--
>>>>>>  net/netfilter/xt_hashlimit.c                  |  5 +-
>>>>>>  net/sctp/protocol.c                           |  7 +--
>>>>>>  security/integrity/ima/ima_kexec.c            |  2 +-
>>>>>>  58 files changed, 195 insertions(+), 144 deletions(-)