Breakdown of changes to Kernel Samepage Merging (KSM) by Kernel Version

This article describes how Linux Kernel Samepage Merging (KSM) has changed.

Overview

Kernel Samepage Merging has changed over the last couple of versions. This document provides an overview of the changes by version. The document will be updated as new kernel versions become available.

6.12

• 32f51ead3d77 mm: remove PageSwapCache

6.11

Optimization for fast changing pages

• d58a361b0350 mm/ksm: don’t waste time searching stable tree for fast changing page

6.10

Several commits to transition to folios.

• c2dc78b86e08 mm/ksm: fix ksm_zero_pages accounting
• 730cdc2c72c6 mm/ksm: fix ksm_pages_scanned accounting

6.9

• No changes.

6.8

• 4e5fa4f5eff6 mm/ksm: add ksm advisor

Adds KSM advisor to dynamically adjust KSM settings.

• 66790e9a735b mm/ksm: add sysfs knobs for advisor
• 5088b49730af mm/ksm: add tracepoint for ksm advisor

Start of work to transition to folios with several commits.

6.7

• e5a689912689 mm/ksm: add pages_skipped metric
• b0540208a59e mm/ksm: document pages_skipped sysfs knob

Add new metric pages scanned in /sys/kernel/mm/ksm/pages_scanned.

• 5e924ff54d08 mm/ksm: add “smart” page scanning mode
• 75d7dd4138ed mm/ksm: document smart scan mode

Add “smart scan” mode to skip pages that have not been de-duplicated in previous scans.

6.6

• 8b47933544a6 proc/ksm: add ksm stats to /proc/pid/smaps

Add KSM information to /proc/<pid>/smaps and /proc/<pid>/smaps_rollup

• d256d1cd8da1 mm: memory-failure: use rcu lock instead of tasklist_lock when collect_procs()
• 5994eabf3bbb merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes
• b348b5fe2b5f mm/ksm: add pages scanned metric

Expose pages scanned metric in /sys/kernel/mm/ksm/pages_scanned

• 1a8e84305783 ksm: consider KSM-placed zeropages when calculating KSM profit

Include zero pages when calculating /sys/kernel/mm/ksm/general_profit

• 6080d19f0704 ksm: add ksm zero pages for each process
• e2942062e01d ksm: count all zero pages placed by KSM
• 79271476b336 ksm: support unsharing KSM-placed zero pages

6.5

• 49b0638502da mm: enable page walking API to lock vmas during the walk
• f985fc322063 mm/swapfile: fix wrong swap entry type for hwpoisoned swapcache page
• 1fec6890bf22 mm: remove references to pagevec
• c33c794828f2 mm: ptep_get() conversion
• 04dee9e85cf5 mm/various: give up if pte_offset_map_lock fails
• 26e1a0c3277d mm: use pmdp_get_lockless() without surplus barrier()

6.4

• 2c281f54f556 mm/ksm: move disabling KSM from s390/gmap code to KSM code
• 24139c07f413 mm/ksm: unmerge and clear VM_MERGEABLE when setting PR_SET_MEMORY_MERGE=0
• d21077fbc2fc mm: add new KSM process and sysfs knobs

• expose new general_profit metric /sys/kernel/mm/ksm/general_profit
• expose process_profit metric in /proc//ksm_stat
• expose ksm_merging_pages metric in /proc//ksm_stat

• d7597f59d1d3 mm: add new api to enable ksm per process

new prctl api to enable KSM per process

• 4248d0083ec5 mm: ksm: support hwpoison for ksm page
• 739100c88f49 mm: add tracepoints to ksm

KSM tracepoints for scan start and stop

6.3

• 6db504ce55bd mm/ksm: fix race with VMA iteration and mm_struct teardown
• f67d6b266493 Merge branch ‘mm-hotfixes-stable’ into mm-stable
• 7d4a8be0c4b2 mm/mmu_notifier: remove unused mmu_notifier_range_update_to_read_only export

6.2

• b970599e807 mm: hwpoison: support recovery from ksm_might_need_to_copy()
• d7c0e68dab98 mm/ksm: convert break_ksm() to use walk_page_range_vma()
• 6cce3314b928 mm/ksm: fix KSM COW breaking with userfaultfd-wp via FAULT_FLAG_UNSHARE
• 58f595c66591 mm/ksm: simplify break_ksm() to not rely on VM_FAULT_WRITE
• 6a56ccbcf6c6 mm/autonuma: use can_change_(pte|pmd)_writable() to replace savedwrite
• 1eeaa4fd39b0 memory: move hotplug memory notifier priority to same file for easy sorting

6.1

• b4e6f66e45b4 ksm: use a folio in replace_page()
• 58730ab6c7ca ksm: convert to use common struct mm_slot
• 79b099415637 ksm: convert ksm_mm_slot.link to ksm_mm_slot.hash
• 23f746e412b4 ksm: convert ksm_mm_slot.mm_list to ksm_mm_slot.mm_node
• 21fbd59136e0 ksm: add the ksm prefix to the names of the ksm private structures
• cb4df4cae4f2 ksm: count allocated ksm rmap_items for each process

Added /proc/<pid>/ksm_stat to report ksm_rmap_items.

• f7091ed64ec8 mm: fix the handling Non-LRU pages returned by follow_page
• a5f18ba07276 mm/ksm: use vma iterators instead of vma linked list
• 088b8aa537c2 mm: fix PageAnonExclusive clearing racing with concurrent RCU GUP-fast
• 507228044236 mm/khugepaged: record SCAN_PMD_MAPPED when scan_pmd() finds hugepage

6.0

• 3218f8712d6b mm: handling Non-LRU pages returned by vm_normal_pages
• 9800562f2ab4 mm/folio-compat: Remove migration compatibility functions