[uClinux-dev] Problem with Memory in uClinux

[Crane, Matthew]

Hi, 

I think you can tweak the kernel policy around keeping free memory
reserved, and how much is reserved for user space vs. kernel.  See
mm/page_alloc.c, include/asm/page.h.  I liked the slub mm to for low-mem
systems. 

Matt

-----Original Message-----
From: uclinux-dev-bounces at uclinux.org
[mailto:uclinux-dev-bounces at uclinux.org] On Behalf Of Gavin Lambert
Sent: Thursday, October 18, 2007 1:42 AM
To: 'uClinux development list'
Subject: RE: [uClinux-dev] Problem with Memory in uClinux

Moments ago, I said:
> >       oom-killer: gfp_mask=0x40d0, order=9
[...]
> Trying to allocate a further 1MB must therefore split the 2MB block in
> half (since there's no VMM it's not possible to stitch smaller blocks
> together).
>
> In any case, allocating 1024KB from the 3040KB free would leave
2016KB.

Actually, come to think of it, an order 9 allocation is 2MB, not 1MB.
(2^9
pages * 4KB per page.)

So you're actually going to be left with 992KB free, which is definitely
below the reserved limit.

This is probably happening because there's a bit of housekeeping
information
attached to each memory allocation by either the kernel or the libc.
This
will increase the required allocation size slightly, and since page
allocations must always be a power of two this is kicking it up to the
next
notch (and doubling the actual allocation).

On my particular setup this allocation overhead is about 8 bytes, but it
might be different on yours.



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