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: https://lore.kernel.org/lkml/202302100915227721315@xxxxxxxxxx/ 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 ---------- v9->v10: ------- (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 'ksm_might_unmap_zero_page'. (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. v8->v9: ------ (1) The previous [PATCH v8 4/6] is squashed into the current [PATCH v9 2/5]. (2) Improve the codes as David's suggestions. v7->v8: ------- (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 features. (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/ v6->v7: ------- 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(-) -- 2.15.2
