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.
I'm not sure what to do about smaps_pmd_entry in that case. We
probably don't care about compund pages.
