The stable kernel is still at v4.19.98 though.
On Wed, Apr 15, 2020 at 8:36 AM Debian Bug Tracking System
<ow...@bugs.debian.org> wrote:
>
> This is an automatic notification regarding your Bug report
> which was filed against the src:linux package:
>
> #953017: linux-image-amd64: Regression from "mm/vmalloc: Sync unmappings in
> __purge_vmap_area_lazy()"
>
> It has been closed by Ben Hutchings <b...@decadent.org.uk>.
>
> Their explanation is attached below along with your original report.
> If this explanation is unsatisfactory and you have not received a
> better one in a separate message then please contact Ben Hutchings
> <b...@decadent.org.uk> by
> replying to this email.
>
>
> --
> 953017: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=953017
> Debian Bug Tracking System
> Contact ow...@bugs.debian.org with problems
>
>
>
> ---------- Forwarded message ----------
> From: Ben Hutchings <b...@decadent.org.uk>
> To: 953017-d...@bugs.debian.org
> Cc:
> Bcc:
> Date: Wed, 15 Apr 2020 01:32:18 +0100
> Subject: Re: Bug#953017: Fixes in Upstream
> 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
>
>
>
>
>
> ---------- Forwarded message ----------
> From: Chen-Yu Tsai <w...@csie.org>
> To: Debian Bug Tracking System <sub...@bugs.debian.org>
> Cc:
> Bcc:
> Date: Tue, 03 Mar 2020 17:51:31 +0800
> Subject: 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
