Re: [PATCH 12/28] readahead: state based method - aging accounting

Wu Fengguang
2006-11-16T13:39:26Z

On Wed, Nov 15, 2006 at 08:54:44AM -0800, Christoph Lameter wrote:
> On Wed, 15 Nov 2006, Wu Fengguang wrote:
>
> > Collect info about the global available memory and its consumption speed.
> > The data are used by the stateful method to estimate the thrashing threshold.
>
> Looks like you should use a ZVC counter for total scanned. See
> include/linux/mmzone.h.

OK.

By using zone.total_scanned, I have chose an easy way :)

To do the general vm timing in something like zone.vm_stat[NR_SCAN_INACTIVE],
a set of new functions will be required:

global_page_state_raw()
zone_page_state_raw()
node_page_state_raw()

They do not check overflows, so that we can do

time_elapsed = new_raw_value - old_raw_value;

However, before introducing the ugly *_raw() functions, I'd like to know if

#ifdef CONFIG_SMP
if (x < 0)
x = 0;
#endif

really helps some big NUMA system. I suspect object counters like
NR_FILE_PAGES will _never_ overflow, and an accumulated counter like
NR_VMSCAN_WRITE is expected to overflow. In either case, it is ok to
return an unsigned long raw counter.

Regards,
Wu