This bug was fixed in the package linux - 6.5.0-5.5
---------------
linux (6.5.0-5.5) mantic; urgency=medium
* mantic/linux: 6.5.0-5.5 -proposed tracker (LP: #2034546)
* Packaging resync (LP: #1786013)
- [Packaging] update helper scripts
- debian/dkms-versions -- update from kernel-versions (main/d2023.08.23)
-- Andrea Righi <andrea.ri...@canonical.com> Wed, 06 Sep 2023 15:51:04
+0200
** Changed in: linux (Ubuntu Mantic)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/2023629
Title:
enable multi-gen LRU by default
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Mantic:
Fix Released
Bug description:
[Impact]
Kernels >= 6.1 have the option to use an alternative least-recently-
used (LRU) page reclaiming mechanism, called multi-gen LRU (MGLRU)
[1].
In short: the kernel used to maintain two LRU lists of "touched"
pages: the "active" and "inactive" list. The former contains pages
thought to be likely used in the future (working set), while the
latter contains pages thought to be less likely used and therefore
likely to be reclaimed when needed. Pages accessed more frequently are
moved to the active list, while pages accessed less frequently are
moved to the inactive list.
The MGLRU generalizes this concept into multiple generations, instead
of just using two lists. Pages move from older to newer generations
when they are accessed and pages from older generations are reclaimed
first when memory is needed. Generations age over time with new
generations being created as the oldest ones are fully reclaimed.
Fedora [2] and Archlinux [3] both have MGLRU enabled by default and
there are plans to enable this also in Debian and openSUSE.
We should also consider to enable this option across the board for
Mantic, considering that in the future MGLRU is likely to become the
default page reclaiming policy in the kernel.
[1] https://lwn.net/Articles/856931/
[2] https://koji.fedoraproject.org/koji/buildinfo?buildID=2168435
[3] https://archlinux.org/packages/core/x86_64/linux-lts/
[Test case]
Apache, MariaDB, memcached, MongoDB, PostreSQL, Redis benchmarks can
all show a performance improvement in terms of operations per sec
switching to MGLRU.
[Fix]
Set CONFIG_LRU_GEN_ENABLED=y in config/annotations.
[Regression potential]
This change is going to affect the page reclaiming policy in the
kernel, so a lot of workloads can be potentially affected by this
change. We may experience *performance regressions* especially in
those systems that are running memory intensive workloads or doing
large amount of I/O (page cache being stressed and lots of page
reclaiming events are happening in the system).
However, considering the benefits of this change, especially in the
cloud/server-oriented scenario, and also considering that this option
is likely to become the "default" page reclaiming mechanism in the
kernel, it makes sense to start using it now so that we can catch
potential regressions in advance and act accordingly.
Moreover, this option can still be adjusted at run-time via
/sys/kernel/mm/lru_gen/enabled, so it's very easy to mitigate any
potential regression and rollback to the old behavior if needed.
To manage notifications about this bug go to:
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