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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>