On 15.08.23 19:10, Stefan Roesch wrote:
David Hildenbrand <david@xxxxxxxxxx> writes:
Sorry for the late reply, Gmail once again decided to classify your mails as
spam (for whatever reason).
On 11.08.23 18:28, Stefan Roesch wrote:
With madvise and prctl KSM can be enabled for different VMA's. Once it
is enabled we can query how effective KSM is overall. However we cannot
easily query if an individual VMA benefits from KSM.
This commit adds a KSM section to the /prod/<pid>/smaps file. It reports
how many of the pages are KSM pages.
Here is a typical output:
7f420a000000-7f421a000000 rw-p 00000000 00:00 0
Size: 262144 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
Rss: 51212 kB
Pss: 8276 kB
Shared_Clean: 172 kB
Shared_Dirty: 42996 kB
Private_Clean: 196 kB
Private_Dirty: 7848 kB
Referenced: 15388 kB
Anonymous: 51212 kB
KSM: 41376 kB
LazyFree: 0 kB
AnonHugePages: 0 kB
ShmemPmdMapped: 0 kB
FilePmdMapped: 0 kB
Shared_Hugetlb: 0 kB
Private_Hugetlb: 0 kB
Swap: 202016 kB
SwapPss: 3882 kB
Locked: 0 kB
THPeligible: 0
ProtectionKey: 0
ksm_state: 0
ksm_skip_base: 0
ksm_skip_count: 0
VmFlags: rd wr mr mw me nr mg anon
This information also helps with the following workflow:
- First enable KSM for all the VMA's of a process with prctl.
- Then analyze with the above smaps report which VMA's benefit the most
- Change the application (if possible) to add the corresponding madvise
calls for the VMA's that benefit the most
Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx>
---
Documentation/filesystems/proc.rst | 3 +++
fs/proc/task_mmu.c | 5 +++++
2 files changed, 8 insertions(+)
diff --git a/Documentation/filesystems/proc.rst
b/Documentation/filesystems/proc.rst
index 7897a7dafcbc..4ef3c0bbf16a 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -461,6 +461,7 @@ Memory Area, or VMA) there is a series of lines such as the following::
Private_Dirty: 0 kB
Referenced: 892 kB
Anonymous: 0 kB
+ KSM: 0 kB
LazyFree: 0 kB
AnonHugePages: 0 kB
ShmemPmdMapped: 0 kB
@@ -501,6 +502,8 @@ accessed.
a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
and a page is modified, the file page is replaced by a private anonymous copy.
+"KSM" shows the amount of anonymous memory that has been de-duplicated.
How do we want to treat memory that has been deduplicated into the shared
zeropage?
It would also match this description.
See in mm-stable:
commit 30ff6ed9a65c7e73545319fc15f7bcf9c52457eb
Author: xu xin <xu.xin16@xxxxxxxxxx>
Date: Tue Jun 13 11:09:28 2023 +0800
ksm: support unsharing KSM-placed zero pages
Patch series "ksm: support tracking KSM-placed zero-pages", v10.
I see two approaches how to deal with zero page:
- If zero page is not enabled, it works as is
- If enabled
- Document that zero page is accounted for the current vma or
- Pass in the pte from smaps_pte_entry() to smaps_account() so we can
determine if this is a zero page.
That's probably the right thing to do: make the stat return the same
value independent of the usage of the shared zeropage.
I'm not sure what to do about smaps_pmd_entry in that case. We
probably don't care about compund pages.
No, KSM only places the shared zeropage for PTEs, no need to handle PMDs.
--
Cheers,
David / dhildenb
