Re: [PATCH] isar-bootstrap: Increase cache room

[Henning Schild <henning.schild@siemens.com>]

Am Tue, 8 May 2018 12:07:55 +0300
schrieb Alexander Smirnov <asmirnov@ilbers.de>:

> On 05/08/2018 11:56 AM, Henning Schild wrote:
> > Am Tue, 8 May 2018 10:56:55 +0300
> > schrieb Alexander Smirnov <asmirnov@ilbers.de>:
> >   
> >> On 05/07/2018 08:12 PM, Henning Schild wrote:  
> >>> Am Mon, 7 May 2018 19:48:16 +0300
> >>> schrieb Alexander Smirnov <asmirnov@ilbers.de>:
> >>>      
> >>>> Hi,
> >>>>
> >>>> On 05/07/2018 07:31 PM, Henning Schild wrote:  
> >>>>> Am Mon, 7 May 2018 18:57:36 +0300
> >>>>> schrieb Alexander Smirnov <asmirnov@ilbers.de>:
> >>>>>         
> >>>>>> On 05/07/2018 06:48 PM, Alexander Smirnov wrote:  
> >>>>>>> According to the man page for 'apt.conf', there are three
> >>>>>>> variables:
> >>>>>>>      - Cache-Start: initial size of mmap cache room
> >>>>>>>      - Cache-Grow: gap for dynamic mmap cache growth
> >>>>>>>      - Cache-Limit: maximal cache size after growth
> >>>>>>>
> >>>>>>> If dynamic resize of mmap region is not avaialbe, the apt uses
> >>>>>>> pre-allocated Cache-Start room [1] for mmap file.
> >>>>>>>
> >>>>>>> Building Isar on one of the Debian host with kernel 3.4, I got
> >>>>>>> the following problem for 'qemuarm64-stretch' configuration:
> >>>>>>>
> >>>>>>> 8<--
> >>>>>>> Hit:1 http://security.debian.org stretch/updates InRelease
> >>>>>>> Ign:2 http://ftp.de.debian.org/debian stretch InRelease
> >>>>>>> Hit:3 http://ftp.de.debian.org/debian stretch-updates
> >>>>>>> InRelease Hit:4 http://ftp.de.debian.org/debian stretch
> >>>>>>> Release E: Dynamic MMap ran out of room. Please increase the
> >>>>>>> size of APT::Cache-Start. Current value: 25165824. (man 5
> >>>>>>> apt.conf) qemu: uncaught target signal 11 (Segmentation
> >>>>>>> fault) - core dumped Segmentation fault 8<--
> >>>>>>>
> >>>>>>> I have no information, why exactly the room could not be
> >>>>>>> re-sized on this system, but it would be better to increase
> >>>>>>> the initial room size for apt. This patch increases the
> >>>>>>> default apt cache twice.  
> >>>>>>
> >>>>>> 1: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=657085
> >>>>>>
> >>>>>> Missed :-(  
> >>>>>
> >>>>> What is your conclusion from that link and what does it mean for
> >>>>> the patch?
> >>>>>         
> >>>>
> >>>> This just the information I found about dynamic cache increasing.
> >>>> Sometimes it could not work. Another fact is that increasing of
> >>>> Cache-Limit doesn't help, so seems that mremap really doesn't
> >>>> work. 
> >>>>> I do not like adding magic numbers and changing the default
> >>>>> config, especially if the whole reason is to work around a
> >>>>> problem only found on outdated build hosts (3.4 really?)  
> >>>>
> >>>> I'm not 100% sure that kernel 3.4 is the source of the problem.
> >>>> Tried to investigate, but for now without results.
> >>>>
> >>>> But if you try to google line:
> >>>>
> >>>>      E: Dynamic MMap ran out of room. Please increase the size of
> >>>> APT::Cache-Start
> >>>>
> >>>> There will be tons of search results, so such problem occurred
> >>>> not only on my host.
> >>>>
> >>>>
> >>>> The man page says:
> >>>>
> >>>> ...on systems with a lot of configured sources it should be
> >>>> increased...
> >>>>
> >>>> so for me it makes sense to increase this room even if there is
> >>>> only one problem report. It doesn't break anything.  
> >>>
> >>> Oh yes it breaks the fact that we do not need to care about the
> >>> value. If you hardcode one today you might be setting half the
> >>> default after the next apt-update. ... because it is a magic
> >>> number and not
> >>>
> >>> set(get()*2)  
> >>
> >> Unfortunately this option is not get-able. It's defined as member
> >> of class in source code, which is initialized on class creation.
> >> There is no getter function to request this variable later.
> >>
> >> 8<--
> >> apt-pkg/pkgcachegen.cc:
> >>
> >> map_filesize_t const MapStart = _config->FindI("APT::Cache-Start",
> >> 24*1024*1024);
> >> ...
> >> return new DynamicMMap(*CacheF, Flags, MapStart, MapGrow,
> >> MapLimit); 8<--
> >>
> >> Anyway, I noticed that build fails later on any 'apt' call in
> >> 'buildchroot' and 'image' for this configuration.
> >>
> >> I was wrong with kernel version, it's 3.16 - the standard Jessie
> >> kernel. So for now, I'd like to drop this patch and add supported
> >> hosts matrix to Isar. This workaround could be described here.  
> > 
> > I guess one could make such a workaround depending on "apt-get
> > --version", to prevent it from causing undesired things in versions
> > it is not for.  
> 
> The problem occurred inside stretch chroot, while host kernel is from 
> jessie. So there should be check for pair: apt version - kernel
> version: if kernel is old, apt is new - then fallback to array-based
> cache.
> 
> Does this look like a hack for you, or not? :-)

Adding the magic-number argument is the real hack. The clearer we can
pin that down to a specific setup, the better. So check the
architecture and temperature as well, if it helps ;).

Henning

> Alex
> 
> > 
> > Henning
> >   
> >> Alex
> >>  
> >>>      
> >>>> We can't require Isar users to always have up-to-dated host
> >>>> systems. If this patch makes all Isar users with old kernels
> >>>> happy, it's probably good for Isar in general :-)  
> >>>
> >>> Sure, but there is a cost ... see previous point.
> >>>        
> >>>>>
> >>>>> If this patch needs to go in, it is missing the cleanup step.
> >>>>>         
> >>>>
> >>>> Sorry, what do you mean here by cleanup step?  
> >>>
> >>> Sorry, misread the patch. I thought it placed a file in the
> >>> rootfs.
> >>>
> >>> Henning
> >>>      
> >>>> Alex
> >>>>     
> >>>>> Henning
> >>>>>         
> >>>>>>> Signed-off-by: Alexander Smirnov <asmirnov@ilbers.de>
> >>>>>>> ---
> >>>>>>>      meta/recipes-core/isar-bootstrap/isar-bootstrap.bb | 4
> >>>>>>> +++- 1 file changed, 3 insertions(+), 1 deletion(-)
> >>>>>>>
> >>>>>>> diff --git
> >>>>>>> a/meta/recipes-core/isar-bootstrap/isar-bootstrap.bb
> >>>>>>> b/meta/recipes-core/isar-bootstrap/isar-bootstrap.bb index
> >>>>>>> a38dd88..4cdefaa 100644 ---
> >>>>>>> a/meta/recipes-core/isar-bootstrap/isar-bootstrap.bb +++
> >>>>>>> b/meta/recipes-core/isar-bootstrap/isar-bootstrap.bb @@
> >>>>>>> -187,7 +187,9 @@ do_apt_update()
> >>>>>>> { E="${@bb.utils.export_proxies(d)}" export
> >>>>>>> DEBIAN_FRONTEND=noninteractive
> >>>>>>> -    sudo -E chroot "${ROOTFSDIR}" /usr/bin/apt-get update -y
> >>>>>>> +    sudo -E chroot "${ROOTFSDIR}" /usr/bin/apt-get update -y
> >>>>>>> \
> >>>>>>> +                                      -o
> >>>>>>> APT::Cache-Start=50331648 +
> >>>>>>>          sudo -E chroot "${ROOTFSDIR}" /usr/bin/apt-get
> >>>>>>> dist-upgrade -y \ -o Debug::pkgProblemResolver=yes
> >>>>>>>      }
> >>>>>>>            
> >>>>>>        
> >>>>>         
> >>>>     
> >>>      
> >>  
> >   
>