On Wed, Jun 22, 2016 at 04:27:57PM +0200, Michal Hocko wrote:
> > which can use it (e.g. vmalloc). I understand how this is both an
> > inherent problem of 32b with a larger high:low ratio and why it is hard
> > to at least pretend we can cope with it with node based approach but we
> > should at least document it.
> >
> > I workaround would be to enable highmem_dirtyable_memory which can lead
> > to premature OOM killer for some workloads AFAIR.
> [...]
> > > static unsigned long highmem_dirtyable_memory(unsigned long total)
> > > {
> > > #ifdef CONFIG_HIGHMEM
> > > - int node;
> > > unsigned long x = 0;
> > > - int i;
> > > -
> > > - for_each_node_state(node, N_HIGH_MEMORY) {
> > > - for (i = 0; i < MAX_NR_ZONES; i++) {
> > > - struct zone *z = &NODE_DATA(node)->node_zones[i];
> > >
> > > - if (is_highmem(z))
> > > - x += zone_dirtyable_memory(z);
> > > - }
> > > - }
>
> Hmm, I have just noticed that we have NR_ZONE_LRU_ANON resp.
> NR_ZONE_LRU_FILE so we can estimate the amount of highmem contribution
> to the global counters by the following or similar:
>
> for_each_node_state(node, N_HIGH_MEMORY) {
> for (i = 0; i < MAX_NR_ZONES; i++) {
> struct zone *z = &NODE_DATA(node)->node_zones[i];
>
> if (!is_highmem(z))
> continue;
>
> x += zone_page_state(z, NR_FREE_PAGES) +
> zone_page_state(z, NR_ZONE_LRU_FILE) - high_wmark_pages(zone);
> }
>
> high wmark reduction would be to emulate the reserve. What do you think?
Agreed with minor modifications. Went with this
for_each_node_state(node, N_HIGH_MEMORY) {
for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
struct zone *z;
if (!is_highmem_idx(z))
continue;
z = &NODE_DATA(node)->node_zones[i];
x += zone_page_state(z, NR_FREE_PAGES) +
zone_page_state(z, NR_ZONE_LRU_FILE) -
high_wmark_pages(zone);
}
}
--
Mel Gorman
SUSE Labs
