David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> writes: > On Thu, Feb 21, 2013 at 10:17:12PM +0530, Aneesh Kumar K.V wrote: >> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> >> >> We now have PTE page consuming only 2K of the 64K page.This is in order to >> facilitate transparent huge page support, which works much better if our PMDs >> cover 16MB instead of 256MB. >> >> Inorder to reduce the wastage, we now have multiple PTE page fragment >> from the same PTE page. > > This needs a much better description of what you're doing here to > manage the allocations. It's certainly not easy to figure out from > the code. I will add more detailed description in the commit message. We allocate one page for the last level of linux page table. With THP and large page size of 16MB, that would mean we are be wasting large part of that page. To map 16MB area, we only need a PTE space of 2K with 64K Page size. This patch reduce the space wastage by sharing the page allocated for the last level of linux page table with multiple pmd entries. We call these smaller chunks PTE page fragments and allocated page, PTE page. We use the page->_mapcount as bitmap to indicate which PTE fragments are free. > > > [snip] >> +#ifdef CONFIG_PPC_64K_PAGES >> +typedef pte_t *pgtable_t; >> +#else >> typedef struct page *pgtable_t; >> +#endif > > This looks really bogus. A pgtable_t is a pointer to PTEs on 64K, but > a pointer to a struct page on 4k. > We enable all the above only with 64K Pages. -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>