Re: fs/stat: Reduce memory requirements for stat_open

[Heiko Carstens <heiko.carstens@de.ibm.com>]

On Thu, Jun 12, 2014 at 03:00:17PM +0200, Stefan Bader wrote:
> When reading from /proc/stat we allocate a large buffer to maximise
> the chances of the results being from a single run and thus internally
> consistent.  This currently is sized at 128 * num_possible_cpus() which,
> in the face of kernels sized to handle large configurations (256 cpus
> plus), results in the buffer being an order-4 allocation or more.
> When system memory becomes fragmented these cannot be guarenteed, leading
> to read failures due to allocation failures.
> 
> There seem to be two issues in play here.  Firstly the allocation is
> going to be vastly over sized in the common case, as we only consume the
> buffer based on the num_online_cpus().  Secondly, regardless of size we
> should not be requiring allocations greater than PAGE_ALLOC_COSTLY_ORDER
> as allocations above this order are significantly more likely to fail.
> 
> The following patch addesses both of these issues.  Does that make sense
> generally? It seemed to stop top complaining wildly for the reporter
> at least.

Hi Stefan,

see also https://lkml.org/lkml/2014/5/21/341

and one possible solution:

https://lkml.org/lkml/2014/5/30/191

and the other one:

https://lkml.org/lkml/2014/6/12/92
https://lkml.org/lkml/2014/6/12/107

Thanks,
Heiko