Re: increased vmap_area_lock contentions on "n_tty: Move buffersinto n_tty_data"

[Peter Hurley]

On 09/26/2013 02:05 PM, Andrew Morton wrote:
> On Thu, 26 Sep 2013 13:35:32 -0400 Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote:
>
> > The issue with a single large kmalloc is that it may fail where
> > 3 separate, page-or-less kmallocs would not have.
>
> Or vmalloc fails first, because of internal fragmentation of the vmap
> arena.  This problem plus vmalloc's slowness are the reasons why
> vmalloc should be avoided.

Ok, no vmalloc.

> A tremendous number of places in the kernel perform higher-order
> allocations nowadays.  The page allocator works damn hard to service
> them and I expect that switching to kmalloc here will be OK.

I've had order-4 allocation failures before on 10Gb. In fact, the
nouveau driver switched to vmalloc for that very reason (commit
d005f51eb93d71cd40ebd11dd377453fa8c8a42a, drm/nouveau: use vmalloc
for pgt allocation).

Regards,
Peter Hurley
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