Re: 2.2/2.4/2.6 VMs: do malloc() ever return NULL?

[Ihar 'Philips' Filipau]

William Lee Irwin III wrote:
> Rik van Riel wrote:
>
> > > Strict non-overcommit mode.  You can allocate as much
> > > non-file-backed virtual memory as will fit in swap,
> > > plus /proc/sys/vm/overcommit_percentage worth of memory.
>
>
> On Wed, Nov 26, 2003 at 11:30:23AM +0100, Ihar 'Philips' Filipau wrote:
>
> >  [ s/overcommit_percentage/overcommit_ratio/ ]
> >  Thanks! On 2.6 it works as expected. Test with two concurrent memory 
> > allocations took some time, but both apps stops exactly when memory was 
> > depleted. Great.
> >  Did rmap has something todo with this?
> >  As I see from implementation of do_mmap_pgoff() - it changed from 2.4 
> > to 2.6 - but there are a lot of common things.
> >  If I will do dumb back port of this check to 2.4 - do you think it 
> > will work? 2.4->2.6 memory accounting changed?
> >  I didn't found this check in your rmap patches for 2.4.22. (btw 
> > thanks for keeping them up-to-date).
>
>
> In principle, non-overcommit shouldn't be dependent on rmap, as it
> largely consists of keeping track of the sum of MAP_PRIVATE virtual
> mappings' sizes and refusing them when they exceed RAM + swap.

  That's the point of my question. I know a few about MM in Linux. As I 
understand memory accounting is most complicated: 1st how to account 
kernel allocatable memory, 2nd how to reliably calculate already 
allocated memory. (1st looks like not present even in 2.6, 2nd not 
present in 2.4.)

  As I understood, default overcommit_ratio=90% is made especially to 
protect kernel from running out of memory. And 2.6 does offset available 
memory by 3% for all non-root allocation checks.

  But I cannot find any similar accounting stuff in 2.4...
  Hard to draw parallels.

  Will appreciate any advice.

--
Ihar 'Philips' Filipau  / with best regards from Saarbruecken.
--                                                           _ _ _
 Because the kernel depends on it existing. "init"          |_|*|_|
 literally _is_ special from a kernel standpoint,           |_|_|*|
 because its' the "reaper of zombies" (and, may I add,      |*|*|*|
 that would be a great name for a rock band).
                                -- Linus Torvalds

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