Messages in this thread | | | Date | Wed, 26 Nov 2003 12:40:28 +1300 | From | Oliver <> | Subject | Re: 2.2/2.4/2.6 VMs: do malloc() ever return NULL? |
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I thought it did return NULL, now... Before that i didn't check for NULL :)
--Oliver
Ihar 'Philips' Filipau wrote:
> Richard B. Johnson wrote: > >> >> As documented, malloc() will never fail as long as there >> is still address space (not memory) available. This is >> the required nature of the over-commit strategy. This is >> necessary because many programs never even touch all the >> memory they allocate. >> > > We are reading different mans? My man malloc(3) clearly states that > malloc() can return NULL. (*) > > May I ask you one question? Did you were ever doing once graceful > failure of application under memory pressure? Looks like not. > > I can guess why sendmail allocates memory it never touches - memory > pools. There are situations where you really cannot fail - and memory > allocation failures are really nasty. Do you wanna to lose your e-mails? > No? So then think twice, while implementing lazy allocators. > > So from my tests I see that by default Linux is not safe. You allocate > memory - malloc() != NULL. Then later you try to write to this memory > and you get killed by oom_killer. What is the point of this? Your > reasoning doesn't sound to me. > > Memory pools used by applications exactly to make grace error > handling under memory pressure - but it looks like this stuff under > Linux gets no testing at all. And default settings could make from > simple bug complete disaster. > > > You can turn OFF over-commit by doing: > > > > echo "2" >proc/sys/vm/overcommit_memory > > > > However, you will probably find that many programs fail > > or seg-fault when normally they wouldn't. So, if you don't > > mind restarting sendmail occasionally, then turn off over-commit. > > > > I shall try overcommit_memory == 2 tomorrow and say what I see. > > P.S. For example application I have ported right now to kernel space has > a limitiation - it must never ever allocate memory: memory consumption > is known, protocol just have no situation like ENOMEM - it _must_ fail > to initialize on start-up. No - not to being killed by oom_killer in > middle of processing. think carrier grade and/or just good programming > technics. > > (*) Great optimization opportunities: remove from all programmes checks > of the return value if malloc(). As by your words - why not? >
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