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

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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@xxxxxxxxxxxxxx>


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(-)




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