Hi!
> I'd like to report a very severe performance regression due to
>
> mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy() in stable kernels
>
> in v4.19.88. I believe this was included since v4.19.67. It is also
> in all the other LTS kernels, except 3.16.
>
> So today I switched an x86_64 production server from v5.1.21 to
> v4.19.88, because we kept hitting runaway kcompactd and kswapd.
> Plus there was a significant increase in memory usage compared to
> v5.1.5. I'm still bisecting that on another production server.
>
> The service we run is one of the largest forums in Taiwan [1].
> It is a terminal-based bulletin board system running over telnet,
> SSH or a custom WebSocket bridge. The service itself is the
> one-process-per-user type of design from the old days. This
> means a lot of forks when there are user spikes or reconnections.
Sounds like fun :-).
I noticed that there's something vmalloc-related in 4.19.89,
Subject: [PATCH 4.19 210/243] x86/mm/32: Sync only to VMALLOC_END in
vmalloc_sync_all()
From: Joerg Roedel <jroedel@xxxxxxx>
commit 9a62d20027da3164a22244d9f022c0c987261687 upstream.
But looking at the changelog again, it may not solve the performance
problem.
Best regards,
Pavel
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DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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