Bug#953017: linux-image-amd64: Regression from "mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()"
Package: linux-image-amd64
Version: 5.4.13-1~bpo10+1
Severity: important
Tags: upstream patch
Dear Maintainer,
A performance regression stemming from the patch "mm/vmalloc: Sync
unmappings in __purge_vmap_area_lazy()" in all mainline and current
stable kernels, except 3.16.y, was reported by multiple persons [1].
The regression involves any activity that exercises vmalloc a lot,
such as creating threads with CONFIG_VMAP_STACK=y or tty allocation
(for example by SSH servers).
A fix [2] for this was posted last October and was picked up in the
-mm tree last November [3]. However this fix did not make it into
v5.6-rc or any other release. It is still only in the -mm tree.
AFAICT this regression only impacts x86 platforms, as it is the only
platform that has a custom vmalloc_sync_all() instead of the standard
no-op stub.
As per my report to upstream, I currently have one production server
running with the offending patch reverted. I also have another with
the fix applied, and that seems to work well.
Please consider adding the fix to Debian kernel images until upstream
kernels have it.
[1] https://www.spinics.net/lists/stable/msg349763.html
[2] https://patchwork.kernel.org/patch/11181159/
[3] https://www.spinics.net/lists/mm-commits/msg141749.html
-- System Information:
Debian Release: 10.3
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: armhf, i386, arm64
Kernel: Linux 5.2.0-0.bpo.2-amd64 (SMP w/8 CPU cores)
Locale: LANG=zh_TW.UTF-8, LC_CTYPE=zh_TW.UTF-8 (charmap=UTF-8), LANGUAGE=zh_TW.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)
Versions of packages linux-image-amd64 depends on:
ii linux-image-5.4.0-0.bpo.3-amd64 5.4.13-1~bpo10+1
linux-image-amd64 recommends no packages.
linux-image-amd64 suggests no packages.
-- no debconf information
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