Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> writes: > 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. > Will try this. -aneesh -- 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>