On Mon, 2013-03-04 at 16:28 +0530, Aneesh Kumar K.V wrote: > I added the below comment when initializing the list. > > +#ifdef CONFIG_PPC_64K_PAGES > + /* > + * Used to support 4K PTE fragment. The pages are added to list, > + * when we have free framents in the page. We track the whether > + * a page frament is available using page._mapcount. A value of > + * zero indicate none of the fragments are used and page can be > + * freed. A value of FRAG_MASK indicate all the fragments are used > + * and hence the page will be removed from the below list. > + */ > + INIT_LIST_HEAD(&init_mm.context.pgtable_list); > +#endif > > I am not sure about why you say there is no consistent rule. Can you > elaborate on that ? Do you really need that list ? I assume it's meant to allow you to find free frags when allocating but my worry is that you'll end up losing quite a bit of node locality of PTE pages.... It may or may not work but can you investigate doing things differently here ? The idea I want you to consider is to always allocate a full page, but make the relationship of the fragments to PTE pages fixed. IE. the fragment in the page is a function of the VA. Basically, the algorithm for allocation is roughly: - Walk the tree down to the PMD ptr (* that can be improved with a generic change, see below) - Check if any of the neighbouring PMDs is populated. If yes, you have your page and pick the appropriate fragment based on the VA - If not, allocate and populate On free, similarly, you checked if all neighbouring PMDs have been cleared, in which case you can fire off the page for RCU freeing. (*) By changing pte_alloc_one to take the PMD ptr (which the call side has right at hand) you can avoid the tree lookup. Cheers, Ben. -- 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>