Re: Free memory starvation in a zone?

[Marcelo Tosatti]

On Fri, 3 Aug 2001, Jeremy Linton wrote:

> In kreclaimd() there is a nice loop that looks like
> 
>  for(i = 0; i < MAX_NR_ZONES; i++) {
>     zone_t *zone = pgdat->node_zones + i;
>     if (!zone->size)
>         continue;
> 
>     while (zone->free_pages < zone->pages_low) {
>         struct page * page;
>         page = reclaim_page(zone);
>         if (!page)
>             break;
>         __free_page(page);
>     }
> }
> 
> I was playing around with the page age algorithm when i noticed that it
> appears that the machine will get into a state where the inner loop _NEVER_
> exits the current zone because applications running in that zone are eating
> the memory as fast as it is being freed up.

Normal allocations are going to block giving a chance for kreclaimd to run
(and remember, the loop and the freeing routines are really fast).

Are you sure you're seeing kreclaimd looping too much here ?

I've never seen that, and if I did I would get really really
concerned: we rely on kreclaimd to avoid atomic allocations from failing
in a fragile way.