Re: Kernel build fails on ARM: Cannot fork: Cannot allocate memory

On Fri, 21 Jun 2013, Zbyszek Bodek wrote:

> On 21.06.2013 01:56, Jeff Roberson wrote:
>> On Thu, 20 Jun 2013, Jeff Roberson wrote:
>>
>>> On Wed, 19 Jun 2013, Zbyszek Bodek wrote:
>>>
>>>> Hello,
>>>>
>>>> I've been trying to compile the kernel on my ARMv7 platform using the
>>>> sources from the current FreeBSD HEAD.
>>>>
>>>> make buildkernel <.....> -j5
>>>>
>>>> 1/2 builds fails in the way described below:
>>>> --------------------------------------------------------------------------
>>>>
>>>> ing-include-dirs -fdiagnostics-show-option   -nostdinc  -I.
>>>> -I/root/src/freebsd-arm-superpages/sys
>>>> -I/root/src/freebsd-arm-superpages/sys/contrib/altq
>>>> -I/root/src/freebsd-arm-superpages/sys/contrib/libfdt -D_KERNEL
>>>> -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h -fno-common
>>>> -finline-limit=8000 --param inline-unit-growth=100 --param
>>>> large-function-growth=1000  -mno-thumb-interwork -ffreestanding -Werror
>>>> /root/src/freebsd-arm-superpages/sys/ufs/ffs/ffs_snapshot.c
>>>> Cannot fork: Cannot allocate memory
>>>> *** [ffs_snapshot.o] Error code 2
>>>> 1 error
>>>> *** [buildkernel] Error code 2
>>>> 1 error
>>>> *** [buildkernel] Error code 2
>>>> 1 error
>>>> 5487.888u 481.569s 7:35.65 1310.0%      1443+167k 1741+5388io 221pf+0w
>>>> --------------------------------------------------------------------------
>>>>
>>>>
>>>> The warning from std err is:
>>>> --------------------------------------------------------------------------
>>>>
>>>> vm_thread_new: kstack allocation failed
>>>> vm_thread_new: kstack allocation failed
>>>> --------------------------------------------------------------------------
>>>>
>>>>
>>>> I was trying to find out which commit is causing this (because I was
>>>> previously working on some older revision) and using bisect I got to:
>>>>
>>>> --------------------------------------------------------------------------
>>>>
>>>> Author: jeff <jeff_at_FreeBSD.org>
>>>> Date:   Tue Jun 18 04:50:20 2013 +0000
>>>>
>>>>    Refine UMA bucket allocation to reduce space consumption and improve
>>>>    performance.
>>>>
>>>>     - Always free to the alloc bucket if there is space.  This gives
>>>> LIFO
>>>>       allocation order to improve hot-cache performance.  This also
>>>> allows
>>>>       for zones with a single bucket per-cpu rather than a pair if the
>>>> entire
>>>>       working set fits in one bucket.
>>>>     - Enable per-cpu caches of buckets.  To prevent recursive bucket
>>>>       allocation one bucket zone still has per-cpu caches disabled.
>>>>     - Pick the initial bucket size based on a table driven maximum size
>>>>       per-bucket rather than the number of items per-page.  This gives
>>>>       more sane initial sizes.
>>>>     - Only grow the bucket size when we face contention on the zone
>>>> lock, this
>>>>       causes bucket sizes to grow more slowly.
>>>>     - Adjust the number of items per-bucket to account for the header
>>>> space.
>>>>       This packs the buckets more efficiently per-page while making them
>>>>       not quite powers of two.
>>>>     - Eliminate the per-zone free bucket list.  Always return buckets
>>>> back
>>>>       to the bucket zone.  This ensures that as zones grow into larger
>>>>       bucket sizes they eventually discard the smaller sizes.  It
>>>> persists
>>>>       fewer buckets in the system.  The locking is slightly trickier.
>>>>     - Only switch buckets in zalloc, not zfree, this eliminates
>>>> pathological
>>>>       cases where we ping-pong between two buckets.
>>>>     - Ensure that the thread that fills a new bucket gets to allocate
>>>> from
>>>>       it to give a better upper bound on allocation time.
>>>>
>>>>    Sponsored by:    EMC / Isilon Storage Division
>>>> --------------------------------------------------------------------------
>>>>
>>>>
>>>> I checked this several times and this commits seems to be causing this.
>>>
>>> Can you tell me how many cores and how much memory you have?  And
>>> paste the output of vmstat -z when you see this error.
>>>
>>> You can try changing bucket_select() at line 339 in uma_core.c to read:
>>>
>>> static int
>>> bucket_select(int size)
>>> {
>>>     return (MAX(PAGE_SIZE / size, 1));
>>> }
>>>
>>> This will approximate the old bucket sizing behavior.
>>
>> Just to add some more information;  On my machine with 16GB of ram the
>> handful of recent UMA commits save about 20MB of kmem on boot.  There
>> are 30% fewer buckets allocated.  And all of the malloc zones have
>> similar amounts of cached space.  Actually the page size malloc bucket
>> is taking up much less space.
>>
>> I don't know if the problem is unique to arm but I have tested x86
>> limited to 512MB of ram without trouble.  I will need the stats I
>> mentioned before to understand what has happened.
>>
>
> Hello Jeff,
>
> Thank you for your interest in my problem.
>
> My system is a quad-core ARMv7 with 2048 MB of RAM on board.
> Please see attachment for the output from vmstat -z when the error occurs.
>
> Changing bucket_select() to
>
> static int
> bucket_select(int size)
> {
>    return (MAX(PAGE_SIZE / size, 1));
> }
>
> as you suggested helps for the problem. I've performed numerous attempts
> to build the kernel and none of them failed.
>

I don't really see a lot of wasted memory in the zones.  There is 
certainly some.  Can you give me sysctl vm from both a working and 
non-working kernel after the build is done or fails?

Thanks,
Jeff


> Best regards
> Zbyszek Bodek
>