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Bug#953017: marked as done (linux-image-amd64: Regression from "mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()")

Your message dated Wed, 15 Apr 2020 01:32:18 +0100
with message-id <efaecb122f4e4341135cd1f9a67e3d92693ffdb8.camel@decadent.org.uk>
and subject line Re: Bug#953017: Fixes in Upstream
has caused the Debian Bug report #953017,
regarding linux-image-amd64: Regression from "mm/vmalloc: Sync unmappings in __purge_vmap_area_lazy()"
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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-- 
953017: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=953017
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
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

--- End Message ---
--- Begin Message --- 
Version: 5.5.13-1

On Thu, 2020-04-09 at 13:40 +0800, Chen-Yu Tsai wrote:
> The fix for this issue has been merged in v5.6-rc7 and is part of the
> v5.6 release. The commit in upstream is:
> 
>     763802b53a42 x86/mm: split vmalloc_sync_all()
> 
> This has also been backported to all current LTS kernels except 3.16
> in the following releases:
> 
>     v4.4.218
>     v4.9.218
>     v4.14.175
>     v4.19.113
>     v5.4.28

...and 5.5.12, so this is fixed in unstable.

Ben.

-- 
Ben Hutchings
It is a miracle that curiosity survives formal education.
                                                      - Albert Einstein

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