On Thu 23-06-16 13:53:12, Mel Gorman wrote:
> 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);
I guess you will still need an underflow protection. Because both free +
lru pages might be below high wmark.
dirtyable += zone_page_state(z, NR_FREE_PAGES) +
zone_page_state(z, NR_ZONE_LRU_FILE);
if (dirtyable > high_wmark_pages(zone)
dirtyable -= high_wmark_pages(zone);
x += dirtyable;
--
Michal Hocko
SUSE Labs
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