On 03/22/2018 02:08 AM, Michal Hocko wrote: > On Wed 21-03-18 17:44:27, Goldwyn Rodrigues wrote: >> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx> >> >> writebacks can recurse into itself under low memory situations. >> Set memalloc_nofs_save() in order to make sure it does not >> recurse. > > How? We are not doing writeback from the direct reclaim context. > I am not sure if I missed a condition in the code, but here is one of the call lineup: writepages() -> writepage() -> kmalloc() -> __alloc_pages() -> __alloc_pages_nodemask -> __alloc_pages_slowpath -> __alloc_pages_direct_reclaim() -> try_to_free_pages() -> do_try_to_free_pages() -> shrink_zones() -> shrink_node() -> shrink_slab() -> do_shrink_slab() -> shrinker.scan_objects() -> super_cache_scan() -> prune_icache_sb() -> fs/inode.c:dispose_list() -> evict(inode) -> evict_inode() for ext4 -> filemap_write_and_wait() -> filemap_fdatawrite(mapping) -> __filemap_fdatawrite_range() -> do_writepages -> writepages() Please note, most filesystems currently have a safeguard in writepage() which will return if the PF_MEMALLOC is set. The other safeguard is __GFP_FS which we are trying to eliminate. -- Goldwyn
