On 30.03.23 16:26, Johannes Weiner wrote:
On Thu, Mar 30, 2023 at 06:55:31AM +0200, David Hildenbrand wrote:
On 29.03.23 01:09, Andrew Morton wrote:
On Fri, 10 Mar 2023 10:28:48 -0800 Stefan Roesch <shr@xxxxxxxxxxxx> wrote:
So far KSM can only be enabled by calling madvise for memory regions. To
be able to use KSM for more workloads, KSM needs to have the ability to be
enabled / disabled at the process / cgroup level.
Review on this series has been a bit thin. Are we OK with moving this
into mm-stable for the next merge window?
I still want to review (traveling this week), but I also don't want to block
this forever.
I think I didn't get a reply from Stefan to my question [1] yet (only some
comments from Johannes). I would still be interested in the variance of
pages we end up de-duplicating for processes.
The 20% statement in the cover letter is rather useless and possibly
misleading if no details about the actual workload are shared.
The workload is instagram. It forks off Django runtimes on-demand
until it saturates whatever hardware it's running on. This benefits
from merging common heap/stack state between instances. Since that
runtime is quite large, the 20% number is not surprising, and matches
our expectations of duplicative memory between instances.
Thanks for this explanation. It's valuable to get at least a feeling for
the workload because it doesn't seem to apply to other workloads at all.
Obviously we could spend months analysing which exact allocations are
identical, and then more months or years reworking the architecture to
deduplicate them by hand and in userspace. But this isn't practical,
and KSM is specifically for cases where this isn't practical.
Based on your request in the previous thread, we investigated whether
the boost was coming from the unintended side effects of KSM splitting
THPs. This wasn't the case.
If you have other theories on how the results could be bogus, we'd be
happy to investigate those as well. But you have to let us know what
you're looking for.
Maybe I'm bad at making such requests but
"Stefan, can you do me a favor and investigate which pages we end up
deduplicating -- especially if it's mostly only the zeropage and if it's
still that significant when disabling THP?"
"In any case, it would be nice to get a feeling for how much variety in
these 20% of deduplicated pages are. "
is pretty clear to me. And shouldn't take months.
Beyond that, I don't think we need to prove from scratch that KSM can
I never expected a proof. I was merely trying to understand if it's
really KSM that helps here. Also with the intention to figure out if KSM
is really the right tool to use here or if it simply "helps by luck" as
with the shared zeropage. That end result could have been valuable to
your use case as well, because KSM overhead is real.
be a worthwhile optimization. It's been established that it can
be. This series is about enabling it in scenarios where madvise()
isn't practical, that's it, and it's yielding the expected results.
I'm sorry to say, but you sound a bit aggressive and annoyed. I also
have no idea why Stefan isn't replying to me but always you.
Am I asking the wrong questions? Do you want me to stop looking at KSM code?
--
Thanks,
David / dhildenb
