Re: [PATCH v2 00/16] Multigenerational LRU Framework

Yu Zhao
2021-04-30T19:32:15Z

On Fri, Apr 30, 2021 at 12:38 AM Konstantin Kharlamov
<hi-angel@yandex.ru> wrote:
>
> Btw, I noticed a fun thing, an improvement. I don't know yet if it can be
> attributed to 5.12 (which I didn't try alone yet) or to the LRU patchset, but
> I'd assume the latter, because 5.12 seems didn't to have had anything
> interesting regarding memory performance¹.

I appreciate the testing and the report. They mean a lot to us.

This improvement is to be expected, and it works both ways. There are
cases that swapping is not a good idea, for example, when building
large repos. Without this patchset, some of my browser memory usually
gets swapped out while tons of memory is used to cache files I don't
really care about.

I completely agree with you on the memory cgroup part: theoretically
it could work around the problem but nobody knows how much memory to
reserve for Skype or Firefox :)

I will keep you posted on the following developments.

Thanks!

> I usually have Skype running in background for work purposes, which is only used
> 2-3 times in a week. So one would expect it to be one the first victims to
> memory reclaim. Unfortunately, I never seen this to actually happen (till now,
> that is): all skypeforlinux processes routinely have 0 bytes in SWAP, and the
> only circumstances under which its processes can get into SWAP is after
> experiencing many SWAP-storms. It was so hard for the kernel to move these
> unused processes to SWAP that at some point I even tried to research if there
> are any odd flags a userspace may have set on a process to keep it in RAM, just
> in case that's what happens to Skype (A: no, that wasn't the case, running Skype
> in a memory limited cgroup makes it swap. It's just that kernel decision were
> lacking for some reason).
>
> So, anyway, I am delighted to see now that while testing this patchset, and
> without encountering even a single SWAP-storm yet, skypeforlinux are one of the
> processes residing in SWAP!!
>
> λ smem -kc "name user pid pss swap" | grep skype
> skypeforlinux constantine 1151 60.0K 7.5M
> skypeforlinux constantine 1215 195.0K 8.1M
> skypeforlinux constantine 1149 706.0K 7.5M
> skypeforlinux constantine 1148 743.0K 7.3M
> skypeforlinux constantine 1307 1.4M 8.0M
> skypeforlinux constantine 1213 2.1M 46.1M
> skypeforlinux constantine 1206 14.0M 10.8M
> skypeforlinux constantine 818 38.5M 34.3M
> skypeforlinux constantine 1242 103.2M 46.8M
>
> !!!
>
> 1: https://kernelnewbies.org/Linux_5.12#Memory_management
>
> On Fri, 2021-04-30 at 02:46 +0300, Konstantin Kharlamov wrote:
> > In case you need it yet, this series is:
> >
> > Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> >
> > My success story: I have Archlinux with 8G RAM + zswap + swap. While developing,
> > I have lots of apps opened such as multiple LSP-servers for different langs,
> > chats, two browsers, etc… Usually, my system gets quickly to a point of SWAP-
> > storms, where I have to kill LSP-servers, restart browsers to free memory, etc,
> > otherwise the system lags heavily and is barely usable.
> >
> > 1.5 day ago I migrated from 5.11.15 kernel to 5.12 + the LRU patchset, and I
> > started up by opening lots of apps to create memory pressure, and worked for a
> > day like this. Till now I had *not a single SWAP-storm*, and mind you I got 3.4G
> > in SWAP. I was never getting to the point of 3G in SWAP before without a single
> > SWAP-storm.
> >
> > Right now my gf on Fedora 33 also suffers from SWAP-storms on her old Macbook
> > 2013 with 4G RAM + zswap + swap, I think the next week I'll build for her 5.12 +
> > LRU patchset as well. Will see how it goes, I expect it will improve her
> > experience by a lot too.
> >
> > P.S.: upon replying please keep me CCed, I'm not subscribed to the list
>