Re: Overcommit_memory logic fails when swap is off

Re: Overcommit_memory logic fails when swap is off

[Martin Egholm Nielsen]

Hello there,

After 2½ year I stumbled over this thread:

> On Wed, 2002-08-21 at 13:23, Alan Cox wrote:
>> 2.5 propses including the ability to set the %age between the 0% of
>> mode 3, the 50 of mode 2 and upwards to things relevant in some
>> embedded system cases. So for 2.6 you will be able to tune it in
>> different ways according to precise understanding of workload.
> Alan, hch or someone asked if it would be possible to merge the 2.5 
> behavior into 2.4-ac ... are you interested or do you not want to 
> break compatibility?

> Note for "mode 2" the behavior is identical. For "mode 3" they would 
> also need to set vm_memory_ratio to "0".

> If you are willing, I'll send you a diff...
 > Robert Love
As I can see, the patch never made it in 2.4.x, right?!
So, I would like a diff - if still possible :-)

I know it's been a while, but I'm stuck with a 2.4 kernel for my 
embedded device and have problems with the OOM...

Best regards,
  Martin Egholm

Re: Overcommit_memory logic fails when swap is off

[Alan Cox]

On Maw, 2005-04-05 at 09:49, Martin Egholm Nielsen wrote:
> As I can see, the patch never made it in 2.4.x, right?!
> So, I would like a diff - if still possible :-)

I submitted it ages ago but it was rejected and punted to 2.6. The 2.4
support is available in Red Hat Enterprise Linux 3, so you can pull it
out of the source rpms on the ftp site or out of Centos etc

Alan

Re: Overcommit_memory logic fails when swap is off

[Martin Egholm Nielsen]

Hi Alan,

>>As I can see, the patch never made it in 2.4.x, right?!
>>So, I would like a diff - if still possible :-)
> I submitted it ages ago but it was rejected and punted to 2.6. The 2.4
> support is available in Red Hat Enterprise Linux 3, so you can pull it
> out of the source rpms on the ftp site or out of Centos etc
Bingo. I seem to have found what looks like it in:
linux-2.4.21-selected-ac-bits.patch
linux-2.4.21-tunable-overcommit.patch

But many of the other patches messes with mmap.c, as well :-), so I 
guess there is some tracking assignment ahead...

But nevertheless, thanks for pointing me to the source...

BR,
  Martin Egholm

Re: Overcommit_memory logic fails when swap is off

[Alan Cox]

On Wed, 2002-08-21 at 18:11, Josip Loncaric wrote:
> Hello,
> 
> I've found some minor logic flaws in mmap.c::vm_enough_memory() which you may
> want to fix.  The problem is simple: overcommit_memory strategies "2" and "3"
> misbehave on machines operated without swap space.  Strategy "2" results in a
> very restrictive memory policy, while strategy "3" crashes the system because
> no memory can be allocated when total_swap_pages is zero.  May I suggest that

The behaviour it provides is correct and intentional. The documentation
is also quite plain on the fact you need swap for mode 3.

Since the kernel needs memory for its own purposes you cannot run
swapless with no overcommit and allow user space all of memory.

2.5 propses including the ability to set the %age between the 0% of mode
3, the 50 of mode 2 and upwards to things relevant in some embedded
system cases. So for 2.6 you will be able to tune it in different ways
according to precise understanding of workload.

As far as your hang goes I'd grab a standard 2.4.19 or 2.4.19-ac4 kernel
and try that.

Re: Overcommit_memory logic fails when swap is off

[Robert Love]

On Wed, 2002-08-21 at 13:23, Alan Cox wrote:

> 2.5 propses including the ability to set the %age between the 0% of mode
> 3, the 50 of mode 2 and upwards to things relevant in some embedded
> system cases. So for 2.6 you will be able to tune it in different ways
> according to precise understanding of workload.

Alan, hch or someone asked if it would be possible to merge the 2.5
behavior into 2.4-ac ... are you interested or do you not want to break
compatibility?

Note for "mode 2" the behavior is identical.  For "mode 3" they would
also need to set vm_memory_ratio to "0".

If you are willing, I'll send you a diff...

	Robert Love

Re: Overcommit_memory logic fails when swap is off

[Alan Cox]

On Wed, 2002-08-21 at 19:04, Robert Love wrote:
> Alan, hch or someone asked if it would be possible to merge the 2.5
> behavior into 2.4-ac ... are you interested or do you not want to break
> compatibility?
> 
> Note for "mode 2" the behavior is identical.  For "mode 3" they would
> also need to set vm_memory_ratio to "0".

Obvious thing to do would be to add the 2.5 feature once its in a Linus
released 2.5 and clearly stable, and make mode 2 mode 3 overwrite that
value when you set them the old way.

I'm happy for that