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Subject[RFC PATCH 0/4] mm: hwpoison: soft-offline support for thp migration
From: Zi Yan <>

Hi Naoya,

Here is soft-offline support for thp migration. I need comments since it has
an interface change (Patch 2) of soft_offline_page() and
a behavior change (Patch 3) in migrate_pages(). soft_offline_page() is used
in store_soft_offline_page() from drivers/base/memory.c.

The patchset is on top of mmotm-2017-08-10-15-33.

The patchset is tested with:
1. simple madvise() call program ( and
2. a local kernel change to intentionally fail allocating THPs for soft offline,
which makes to-be-soft-offlined THPs being split by Patch 3.

Patch 1: obtain the size of a offlined page before it is offlined. The size is
used as the step value of the for-loop inside madvise_inject_error().
Originally, the for-loop used the size of offlined pages, which was OK.
But as a THP is offlined, it is split afterwards, so the page size obtained
after offlined is PAGE_SIZE instead of THP page size, which causes a THP being
offlined 512 times.

Patch 2: when offlining a THP, there are two situations, a) the THP is offlined
as a whole, or b) the THP is split and only the raw error page is offlined.
Thus, we need soft_offline_page() to tell us whether a THP is split during
offlining, which leads to a new interface parameter.

Patch 3: as Naoya suggested, if a THP fails to be offlined as a whole, we should
retry the raw error subpage. This patch implement it. This also requires
migrate_pages() not splitting a THP if migration fails for MR_MEMORY_FAILURE.

Patch 4: enable thp migration support for soft offline.

Any suggestions and comments are welcome.


Zi Yan (4):
mm: madvise: read loop's step size beforehand in
madvise_inject_error(), prepare for THP support.
mm: soft-offline: Change soft_offline_page() interface to tell if the
page is split or not.
mm: soft-offline: retry to split and soft-offline the raw error if the
original THP offlining fails.
mm: hwpoison: soft offline supports thp migration

drivers/base/memory.c | 2 +-
include/linux/mm.h | 2 +-
mm/madvise.c | 24 ++++++++++--
mm/memory-failure.c | 103 +++++++++++++++++++++++++++++---------------------
mm/migrate.c | 16 ++++++++
5 files changed, 97 insertions(+), 50 deletions(-)


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