Rework the existing mmu_gather infrastructure. The direct purpose of these patches was to allow preemptible mmu_gather, but even without that I think these patches provide an improvement to the status quo. The first 9 patches rework the mmu_gather infrastructure. For review purpose I've split them into generic and per-arch patches with the last of those a generic cleanup. The next patch provides generic RCU page-table freeing, and the followup is a patch converting s390 to use this. I've also got 4 patches from DaveM lined up (not included in this series) that uses this to implement gup_fast() for sparc64. Then there is one patch that extends the generic mmu_gather batching. After that follow the mm preemptibility patches, these make part of the mm a lot more preemptible. It converts i_mmap_lock and anon_vma->lock to mutexes which together with the mmu_gather rework makes mmu_gather preemptible as well. Making i_mmap_lock a mutex also enables a clean-up of the truncate code. This also allows for preemptible mmu_notifiers, something that XPMEM I think wants. Furthermore, it removes the new and universially detested unmap_mutex. This patch: Remove the first obstacle towards a fully preemptible mmu_gather. The current scheme assumes mmu_gather is always done with preemption disabled and uses per-cpu storage for the page batches. Change this to try and allocate a page for batching and in case of failure, use a small on-stack array to make some progress. Preemptible mmu_gather is desired in general and usable once i_mmap_lock becomes a mutex. Doing it before the mutex conversion saves us from having to rework the code by moving the mmu_gather bits inside the pte_lock. Also avoid flushing the tlb batches from under the pte lock, this is useful even without the i_mmap_lock conversion as it significantly reduces pte lock hold times. [akpm@linux-foundation.org: fix comment tpyo] Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: David Miller <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Paul Mundt <lethal@linux-sh.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Tony Luck <tony.luck@intel.com> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Hugh Dickins <hughd@google.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Nick Piggin <npiggin@kernel.dk> Cc: Namhyung Kim <namhyung@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
191 lines
5.0 KiB
C
191 lines
5.0 KiB
C
/* include/asm-generic/tlb.h
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*
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* Generic TLB shootdown code
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*
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* Copyright 2001 Red Hat, Inc.
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* Based on code from mm/memory.c Copyright Linus Torvalds and others.
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*
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* Copyright 2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#ifndef _ASM_GENERIC__TLB_H
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#define _ASM_GENERIC__TLB_H
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#include <linux/swap.h>
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#include <asm/pgalloc.h>
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#include <asm/tlbflush.h>
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/*
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* For UP we don't need to worry about TLB flush
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* and page free order so much..
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*/
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#ifdef CONFIG_SMP
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#define tlb_fast_mode(tlb) ((tlb)->nr == ~0U)
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#else
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#define tlb_fast_mode(tlb) 1
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#endif
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/*
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* If we can't allocate a page to make a big batch of page pointers
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* to work on, then just handle a few from the on-stack structure.
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*/
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#define MMU_GATHER_BUNDLE 8
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/* struct mmu_gather is an opaque type used by the mm code for passing around
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* any data needed by arch specific code for tlb_remove_page.
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*/
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struct mmu_gather {
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struct mm_struct *mm;
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unsigned int nr; /* set to ~0U means fast mode */
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unsigned int max; /* nr < max */
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unsigned int need_flush;/* Really unmapped some ptes? */
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unsigned int fullmm; /* non-zero means full mm flush */
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#ifdef HAVE_ARCH_MMU_GATHER
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struct arch_mmu_gather arch;
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#endif
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struct page **pages;
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struct page *local[MMU_GATHER_BUNDLE];
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};
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static inline void __tlb_alloc_page(struct mmu_gather *tlb)
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{
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unsigned long addr = __get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
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if (addr) {
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tlb->pages = (void *)addr;
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tlb->max = PAGE_SIZE / sizeof(struct page *);
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}
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}
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/* tlb_gather_mmu
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* Called to initialize an (on-stack) mmu_gather structure for page-table
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* tear-down from @mm. The @fullmm argument is used when @mm is without
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* users and we're going to destroy the full address space (exit/execve).
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*/
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static inline void
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tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm)
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{
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tlb->mm = mm;
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tlb->max = ARRAY_SIZE(tlb->local);
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tlb->pages = tlb->local;
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if (num_online_cpus() > 1) {
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tlb->nr = 0;
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__tlb_alloc_page(tlb);
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} else /* Use fast mode if only one CPU is online */
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tlb->nr = ~0U;
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tlb->fullmm = fullmm;
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#ifdef HAVE_ARCH_MMU_GATHER
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tlb->arch = ARCH_MMU_GATHER_INIT;
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#endif
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}
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static inline void
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tlb_flush_mmu(struct mmu_gather *tlb)
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{
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if (!tlb->need_flush)
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return;
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tlb->need_flush = 0;
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tlb_flush(tlb);
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if (!tlb_fast_mode(tlb)) {
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free_pages_and_swap_cache(tlb->pages, tlb->nr);
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tlb->nr = 0;
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/*
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* If we are using the local on-stack array of pages for MMU
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* gather, try allocating an off-stack array again as we have
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* recently freed pages.
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*/
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if (tlb->pages == tlb->local)
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__tlb_alloc_page(tlb);
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}
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}
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/* tlb_finish_mmu
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* Called at the end of the shootdown operation to free up any resources
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* that were required.
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*/
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static inline void
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tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
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{
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tlb_flush_mmu(tlb);
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/* keep the page table cache within bounds */
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check_pgt_cache();
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if (tlb->pages != tlb->local)
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free_pages((unsigned long)tlb->pages, 0);
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}
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/* __tlb_remove_page
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* Must perform the equivalent to __free_pte(pte_get_and_clear(ptep)), while
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* handling the additional races in SMP caused by other CPUs caching valid
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* mappings in their TLBs. Returns the number of free page slots left.
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* When out of page slots we must call tlb_flush_mmu().
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*/
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static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
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{
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tlb->need_flush = 1;
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if (tlb_fast_mode(tlb)) {
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free_page_and_swap_cache(page);
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return 1; /* avoid calling tlb_flush_mmu() */
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}
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tlb->pages[tlb->nr++] = page;
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VM_BUG_ON(tlb->nr > tlb->max);
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return tlb->max - tlb->nr;
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}
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/* tlb_remove_page
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* Similar to __tlb_remove_page but will call tlb_flush_mmu() itself when
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* required.
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*/
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static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
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{
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if (!__tlb_remove_page(tlb, page))
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tlb_flush_mmu(tlb);
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}
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/**
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* tlb_remove_tlb_entry - remember a pte unmapping for later tlb invalidation.
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*
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* Record the fact that pte's were really umapped in ->need_flush, so we can
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* later optimise away the tlb invalidate. This helps when userspace is
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* unmapping already-unmapped pages, which happens quite a lot.
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*/
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#define tlb_remove_tlb_entry(tlb, ptep, address) \
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do { \
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tlb->need_flush = 1; \
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__tlb_remove_tlb_entry(tlb, ptep, address); \
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} while (0)
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#define pte_free_tlb(tlb, ptep, address) \
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do { \
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tlb->need_flush = 1; \
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__pte_free_tlb(tlb, ptep, address); \
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} while (0)
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#ifndef __ARCH_HAS_4LEVEL_HACK
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#define pud_free_tlb(tlb, pudp, address) \
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do { \
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tlb->need_flush = 1; \
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__pud_free_tlb(tlb, pudp, address); \
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} while (0)
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#endif
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#define pmd_free_tlb(tlb, pmdp, address) \
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do { \
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tlb->need_flush = 1; \
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__pmd_free_tlb(tlb, pmdp, address); \
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} while (0)
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#define tlb_migrate_finish(mm) do {} while (0)
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#endif /* _ASM_GENERIC__TLB_H */
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