On 04/09, Minchan Kim wrote: > On Mon, Apr 09, 2018 at 04:14:03AM -0700, Matthew Wilcox wrote: > > On Mon, Apr 09, 2018 at 12:09:30PM +0900, Minchan Kim wrote: > > > On Sun, Apr 08, 2018 at 07:49:25PM -0700, Matthew Wilcox wrote: > > > > On Mon, Apr 09, 2018 at 10:58:15AM +0900, Minchan Kim wrote: > > > > > It assumes shadow entry of radix tree relies on the init state > > > > > that node->private_list allocated should be list_empty state. > > > > > Currently, it's initailized in SLAB constructor which means > > > > > node of radix tree would be initialized only when *slub allocates > > > > > new page*, not *new object*. So, if some FS or subsystem pass > > > > > gfp_mask to __GFP_ZERO, slub allocator will do memset blindly. > > > > > > > > Wait, what? Who's declaring their radix tree with GFP_ZERO flags? > > > > I don't see anyone using INIT_RADIX_TREE or RADIX_TREE or RADIX_TREE_INIT > > > > with GFP_ZERO. > > > > > > Look at fs/f2fs/inode.c > > > mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO); > > > > > > __add_to_page_cache_locked > > > radix_tree_maybe_preload > > > > > > add_to_page_cache_lru > > > > > > What's the wrong with setting __GFP_ZERO with mapping->gfp_mask? > > > > Because it's a stupid thing to do. Pages are allocated and then filled > > from disk. Zeroing them before DMAing to them is just a waste of time. > > Every FSes do address_space to read pages from storage? I'm not sure. > > If you're right, we need to insert WARN_ON to catch up __GFP_ZERO > on mapping_set_gfp_mask at the beginning and remove all of those > stupid thins. > > Jaegeuk, why do you need __GFP_ZERO? Could you explain? Comment says "__GFP_ZERO returns a zeroed page on success." The f2fs maintains two inodes to manage some metadata in the page cache, which requires zeroed data when introducing a new structure. It's not a big deal to avoid __GFP_ZERO for whatever performance reasons tho, does it only matters with f2fs? Thanks,
