Re: Memory management woes - order 1 allocation failures

From: Alan Cox
Date: Tue Mar 02 2010 - 13:32:37 EST

> For reasons that are not particularly clear to me, tty_buffer_alloc() is
> called far more frequently in 2.6.33 than in 2.6.24. I instrumented the
> function to print out the size of the buffers allocated, booted under
> qemu and would just "cat /bin/ls" to see what buffers were allocated.
> 2.6.33 allocates loads, including high-order allocations. 2.6.24
> appeared to allocate once and keep silent.

The pty layer is using them now and didn't before. That will massively
distort your numhers.

> While there have been snags recently with respect to high-order
> allocation failures in recent kernels, this might be one of the cases
> where it's due to subsystems requesting high-order allocations more.

The pty code certainly triggered more such allocations. I've sent Greg
patches to make the tty buffering layer allocate sensible sizes as it
doesn't need multiple page allocations in the first place.

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