[PATCH v10 0/5] ksm: support tracking KSM-placed zero-pages

From: yang.yang29
Date: Thu May 25 2023 - 01:42:11 EST

From: xu xin <xu.xin16@xxxxxxxxxx>

The core idea of this patch set is to enable users to perceive the number
of any pages merged by KSM, regardless of whether use_zero_page switch has
been turned on, so that users can know how much free memory increase is
really due to their madvise(MERGEABLE) actions. But the problem is, when
enabling use_zero_pages, all empty pages will be merged with kernel zero
pages instead of with each other as use_zero_pages is disabled, and then
these zero-pages are no longer monitored by KSM.

The motivations to do this is seen at:

In one word, we hope to implement the support for KSM-placed zero pages
tracking without affecting the feature of use_zero_pages, so that app
developer can also benefit from knowing the actual KSM profit by getting
KSM-placed zero pages to optimize applications eventually when
/sys/kernel/mm/ksm/use_zero_pages is enabled.

Change log
(1) Fix a compile error due to [PATCH v8 3/5] when CONFIG_KSM is not set.

(2) Rename the function 'ksm_notify_unmap_zero_page' as

(3) In [PATCH 5/5], we get ksm_zero_pages from its own 'mm' instead of
the global system.

(4) In [PATCH 5/5], we add a subject task of testing ksm zero pages when
unmerging by triggering write fault.

(1) The previous [PATCH v8 4/6] is squashed into the current [PATCH v9 2/5].

(2) Improve the codes as David's suggestions.

(1) Since [1] which fix the bug of pte_mkdirty on sparc64 that makes pte
writable, then we can remove the architechture restrictions of our
(2) Improve the scheme of update ksm_zero_pages: add the handling case when
khugepaged replaces a shared zeropage by a THP.

[1] https://lore.kernel.org/all/20230411141529.428991-2-david@xxxxxxxxxx/

This is an all-newed version which is different from v6 which relys on KSM's
rmap_item. The patch series don't rely on rmap_item but pte_dirty, so the
general handling of tracking KSM-placed zero-pages is simplified a lot.

For safety, we restrict this feature only to the tested and known-working
architechtures (ARM, ARM64, and X86) fow now.

xu xin (5):
ksm: support unsharing KSM-placed zero pages
ksm: count all zero pages placed by KSM
ksm: add ksm zero pages for each process
ksm: consider KSM-placed zeropages when calculating KSM profit
selftest: add a testcase of ksm zero pages

Documentation/admin-guide/mm/ksm.rst | 25 ++++--
fs/proc/base.c | 1 +
include/linux/ksm.h | 20 +++++
include/linux/mm_types.h | 9 ++-
mm/khugepaged.c | 2 +
mm/ksm.c | 28 +++++--
mm/memory.c | 5 +-
tools/testing/selftests/mm/ksm_functional_tests.c | 98 ++++++++++++++++++++++-
8 files changed, 172 insertions(+), 16 deletions(-)