On Tue, Apr 10, 2018 at 08:04:09AM +0900, Minchan Kim wrote: > On Mon, Apr 09, 2018 at 08:20:32AM -0700, Matthew Wilcox wrote: > > I don't think this is something the radix tree should know about. > > Because shadow entry implementation is hidden by radix tree implemetation. > IOW, radix tree user cannot know how it works.
I have no idea what you mean. > > SLAB should be checking for it (the patch I posted earlier in this > > I don't think it's right approach. SLAB constructor can initialize > some metadata for slab page populated as well as page zeroing. > However, __GFP_ZERO means only clearing pages, not metadata. > So it's different semantic. No need to mix out. No, __GFP_ZERO is specified to clear the allocated memory whether you're allocating from alloc_pages or from slab. What makes no sense is allocating an object from slab with a constructor *and* __GFP_ZERO. They're in conflict, and slab can't fulfill both of those requirements. > > thread), but the right place to filter this out is in the caller of > > radix_tree_maybe_preload -- it's already filtering out HIGHMEM pages, > > and should filter out GFP_ZERO too. > > radix_tree_[maybe]_preload is exported API, which are error-prone > for out of modules or upcoming customers. > > More proper place is __radix_tree_preload. I could not disagree with you more. It is the responsibility of the callers of radix_tree_preload to avoid calling it with nonsense flags like __GFP_DMA, __GFP_HIGHMEM or __GFP_ZERO.