On Fri 01-06-18 16:50:50, Sahitya Tummala wrote: > On Fri, Jun 01, 2018 at 12:26:09PM +0200, Michal Hocko wrote: > > On Fri 01-06-18 15:02:35, Sahitya Tummala wrote: > > > Hi, > > > > > > We are observing a deadlock scenario during FS writeback under low-memory > > > condition with F2FS filesystem. > > > > > > Here is the callstack of this scenario - > > > > > > shrink_inactive_list() > > > shrink_node_memcg.isra.74() > > > shrink_node() > > > shrink_zones(inline) > > > do_try_to_free_pages(inline) > > > try_to_free_pages() > > > __perform_reclaim(inline) > > > __alloc_pages_direct_reclaim(inline) > > > __alloc_pages_slowpath(inline) > > > no_zone() > > > __alloc_pages(inline) > > > __alloc_pages_node(inline) > > > alloc_pages_node(inline) > > > __page_cache_alloc(inline) > > > pagecache_get_page() > > > find_or_create_page(inline) > > > grab_cache_page(inline) > > > f2fs_grab_cache_page(inline) > > > __get_node_page.part.32() > > > __get_node_page(inline) > > > get_node_page() > > > update_inode_page() > > > f2fs_write_inode() > > > write_inode(inline) > > > __writeback_single_inode() > > > writeback_sb_inodes() > > > __writeback_inodes_wb() > > > wb_writeback() > > > wb_do_writeback(inline) > > > wb_workfn() > > > > > > The writeback thread is entering into the direct reclaim path due to low-memory and is > > > getting stuck in shrink_inactive_list(), as shrink_inactive_list() is inturn waiting for > > > writeback to happen for the dirty pages present in the inactive list. > > > > shrink_page_list waits only for writeback pages when we are in the memcg > > reclaim. The above seems to be the global reclaim though. Moreover > > GFP_F2FS_ZERO is GFP_NOFS so we are not waiting for writeback pages at > > all. Are you sure the above is really a deadlock? > > > > Let me correct my statement. It could be more of a livelock scenario. > > The direct reclaim path is not doing any writeback here, so the GFP_NOFS doesn't > make any difference. In this case, the direct reclaim has to reclaim ~32 pages, > which it picks up from the tail of the list. All of those tail pages are dirty > and since direct reclaim path can't do any writeback, it just loops picking and > skipping them. But there are surely other pages on the LRU list, aren't they? -- Michal Hocko SUSE Labs
