Hi Peter, On Thu, Sep 13, 2018 at 11:21:11AM +0200, Peter Zijlstra wrote: > Write a comment explaining some of this.. This comment is much-needed, thanks! Some comments inline. > + * The mmu_gather API consists of: > + * > + * - tlb_gather_mmu() / tlb_finish_mmu(); start and finish a mmu_gather > + * > + * Finish in particular will issue a (final) TLB invalidate and free > + * all (remaining) queued pages. > + * > + * - tlb_start_vma() / tlb_end_vma(); marks the start / end of a VMA > + * > + * Defaults to flushing at tlb_end_vma() to reset the range; helps when > + * there's large holes between the VMAs. > + * > + * - tlb_remove_page() / __tlb_remove_page() > + * - tlb_remove_page_size() / __tlb_remove_page_size() > + * > + * __tlb_remove_page_size() is the basic primitive that queues a page for > + * freeing. __tlb_remove_page() assumes PAGE_SIZE. Both will return a > + * boolean indicating if the queue is (now) full and a call to > + * tlb_flush_mmu() is required. > + * > + * tlb_remove_page() and tlb_remove_page_size() imply the call to > + * tlb_flush_mmu() when required and has no return value. > + * > + * - tlb_change_page_size() This doesn't seem to exist in my tree. [since realised you rename to it in the next patch] > + * > + * call before __tlb_remove_page*() to set the current page-size; implies a > + * possible tlb_flush_mmu() call. > + * > + * - tlb_flush_mmu() / tlb_flush_mmu_tlbonly() / tlb_flush_mmu_free() > + * > + * tlb_flush_mmu_tlbonly() - does the TLB invalidate (and resets > + * related state, like the range) > + * > + * tlb_flush_mmu_free() - frees the queued pages; make absolutely > + * sure no additional tlb_remove_page() > + * calls happen between _tlbonly() and this. > + * > + * tlb_flush_mmu() - the above two calls. > + * > + * - mmu_gather::fullmm > + * > + * A flag set by tlb_gather_mmu() to indicate we're going to free > + * the entire mm; this allows a number of optimizations. > + * > + * XXX list optimizations On arm64, we can elide the invalidation altogether because we won't re-allocate the ASID. We also have an invalidate-by-ASID (mm) instruction, which we could use if we needed to. > + * > + * - mmu_gather::need_flush_all > + * > + * A flag that can be set by the arch code if it wants to force > + * flush the entire TLB irrespective of the range. For instance > + * x86-PAE needs this when changing top-level entries. > + * > + * And requires the architecture to provide and implement tlb_flush(). > + * > + * tlb_flush() may, in addition to the above mentioned mmu_gather fields, make > + * use of: > + * > + * - mmu_gather::start / mmu_gather::end > + * > + * which (when !need_flush_all; fullmm will have start = end = ~0UL) provides > + * the range that needs to be flushed to cover the pages to be freed. I don't understand the mention of need_flush_all here -- I didn't think it was used by the core code at all. > + * > + * - mmu_gather::freed_tables > + * > + * set when we freed page table pages > + * > + * - tlb_get_unmap_shift() / tlb_get_unmap_size() > + * > + * returns the smallest TLB entry size unmapped in this range > + * > + * Additionally there are a few opt-in features: > + * > + * HAVE_MMU_GATHER_PAGE_SIZE > + * > + * This ensures we call tlb_flush() every time tlb_change_page_size() actually > + * changes the size and provides mmu_gather::page_size to tlb_flush(). Ah, you add this later in the series. I think Nick reckoned we could get rid of this (the page_size field) eventually... Will
