[Geany] do not open oversize files

[Lex Trotman]

On 6 January 2011 06:14, Dimitar Zhekov <dimitar.zhekov at gmail.com> wrote:
> On Wed, 5 Jan 2011 11:08:18 +1100
> Lex Trotman <elextr at gmail.com> wrote:
>
>> And on modern kernels virtual memory can be overcommitted
>> significantly so it may not work
>
> I haven't said that a successful alloc guarantees everything will be
> fine. :)

Understand, I just think that overcommit capability means that it errs
on the unsafe side which is the wrong way to avoid lockups.

But with the kernel defaults, you'll at least catch the most
> obvious cases.

IIUC the default is to overcommit, but I guess it depends on what your
distro sets, I no longer bother to compile kernels.

>
>> is expensive since the page tables have to be constructed even if
>> the memory is not used.
>
> CPU cost: that's only once per file, memory cost: < 1%
>
>> Also this could cause fragmentation of the virtual address space that
>> may limit how many times it will work.
>
> Yes, or some other problems. It's a hack, and should only be used if
> we can't agree on anything better. Personally I'm for a preference.

Agree, I'm just trying to point out some risks in support of the
preference option.

>
> ---
>
> On Tue, 4 Jan 2011 22:05:52 +0100
> Krzysztof Żelechowski <giecrilj at stegny.2a.pl> wrote:
>
>> > > I do not know where you got it from, but the last OS I know that
>> > > behaved like that was MacOS 7. [cut]
>> >
>> > Like what?..
>>
>> Like necessarily allocating a contiguous block of physical memory.
>
> What a strange idea... Unless your CPU lacks MMU, of course.
>
>> GNU malloc uses mmap so it is all virtual.
>
> mmap for large blocks and heap for small blocks IIRC, and naturally, the
> heap itself is mmap-ed.

But what does windows do??  Don't want more differences between
versions to maintain.

>
>> > If by "01 << 040" you mean 4GB, how much real and virtual memory do
>> > you have?
>> >
>> >
>>
>> I have 1 GB of physical memory.  (01 << 040) is the first integer that does not fit into unsigned int.
>
> So then, using more than 4GB _will_ be a problem on your system, QED.
> I pointed out it's a rough check.
>
> But if your malloc() fails on 4GB, and not below that, you either have
> an unusually large swap file, or your kernel is set to always
> overcommit. With the defaults, the check works much better.

And you have a 64 bit kernel.

Cheers
Lex
>
> --
> E-gards: Jimmy
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