From: xu xin xu.xin16@zte.com.cn
This series aim to fix exec/fork inheritance and introduce ksm-utils tools including ksm-set and ksm-get, you can see the detail in PATCH 1.
Problem ======= In some extreme scenarios, however, this inheritance of MMF_VM_MERGE_ANY during exec/fork can fail. For example, when the scanning frequency of ksmd is tuned extremely high, a process carrying MMF_VM_MERGE_ANY may still fail to pass it to the newly exec'd process. This happens because ksm_execve() is executed too early in the do_execve flow (prematurely adding the new mm_struct to the ksm_mm_slot list).
As a result, before do_execve completes, ksmd may have already performed a scan and found that this new mm_struct has no VM_MERGEABLE VMAs, thus clearing its MMF_VM_MERGE_ANY flag. Consequently, when the new program executes, the flag MMF_VM_MERGE_ANY inheritance fails!
Reproduce ======== Prepare ksm-utils in the prerequisite PATCH, and simply do as follows
echo 1 > /sys/kernel/mm/ksm/run; echo 2000 > /sys/kernel/mm/ksm/pages_to_scan; echo 0 > /sys/kernel/mm/ksm/sleep_millisecs; ksm-set -s on [NEW_PROGRAM_BIN] & ksm-get -a -e
you can see like this: Pid Comm Merging_pages Ksm_zero_pages Ksm_profit Ksm_mergeable Ksm_merge_any 206 NEW_PROGRAM_BIN 7680 0 30965760 yes no
Note: If the first time don't reproduce the issue, pkill NEW_PROGRAM_BIN and try run it again. Usually, we can reproduce it in 5 times.
Root reason =========== The commit d7597f59d1d33 ("mm: add new api to enable ksm per process") clear the flag MMF_VM_MERGE_ANY when ksmd found no VM_MERGEABLE VMAs.
xu xin (2): tools: add ksm-utils tools mm/ksm: fix exec/fork inheritance support for prctl
mm/ksm.c | 8 +- tools/mm/Makefile | 12 +- tools/mm/ksm-utils/Makefile | 10 + tools/mm/ksm-utils/ksm-get.c | 397 +++++++++++++++++++++++++++++++++++ tools/mm/ksm-utils/ksm-set.c | 144 +++++++++++++ 5 files changed, 567 insertions(+), 4 deletions(-) create mode 100644 tools/mm/ksm-utils/Makefile create mode 100644 tools/mm/ksm-utils/ksm-get.c create mode 100644 tools/mm/ksm-utils/ksm-set.c