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authorSagi Grimberg <sagig@mellanox.com>2012-10-08 16:33:33 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-09 16:22:58 +0900
commit2ec74c3ef2d8c58d71e0e00336fb6b891192155a (patch)
tree512b591504cdbee278c27afc50a7e3a558b4851a /include
parent36e4f20af833d1ce196e6a4ade05dc26c44652d1 (diff)
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mm: move all mmu notifier invocations to be done outside the PT lock
In order to allow sleeping during mmu notifier calls, we need to avoid invoking them under the page table spinlock. This patch solves the problem by calling invalidate_page notification after releasing the lock (but before freeing the page itself), or by wrapping the page invalidation with calls to invalidate_range_begin and invalidate_range_end. To prevent accidental changes to the invalidate_range_end arguments after the call to invalidate_range_begin, the patch introduces a convention of saving the arguments in consistently named locals: unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ ... mmun_start = ... mmun_end = ... mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); ... mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); The patch changes code to use this convention for all calls to mmu_notifier_invalidate_range_start/end, except those where the calls are close enough so that anyone who glances at the code can see the values aren't changing. This patchset is a preliminary step towards on-demand paging design to be added to the RDMA stack. Why do we want on-demand paging for Infiniband? Applications register memory with an RDMA adapter using system calls, and subsequently post IO operations that refer to the corresponding virtual addresses directly to HW. Until now, this was achieved by pinning the memory during the registration calls. The goal of on demand paging is to avoid pinning the pages of registered memory regions (MRs). This will allow users the same flexibility they get when swapping any other part of their processes address spaces. Instead of requiring the entire MR to fit in physical memory, we can allow the MR to be larger, and only fit the current working set in physical memory. Why should anyone care? What problems are users currently experiencing? This can make programming with RDMA much simpler. Today, developers that are working with more data than their RAM can hold need either to deregister and reregister memory regions throughout their process's life, or keep a single memory region and copy the data to it. On demand paging will allow these developers to register a single MR at the beginning of their process's life, and let the operating system manage which pages needs to be fetched at a given time. In the future, we might be able to provide a single memory access key for each process that would provide the entire process's address as one large memory region, and the developers wouldn't need to register memory regions at all. Is there any prospect that any other subsystems will utilise these infrastructural changes? If so, which and how, etc? As for other subsystems, I understand that XPMEM wanted to sleep in MMU notifiers, as Christoph Lameter wrote at http://lkml.indiana.edu/hypermail/linux/kernel/0802.1/0460.html and perhaps Andrea knows about other use cases. Scheduling in mmu notifications is required since we need to sync the hardware with the secondary page tables change. A TLB flush of an IO device is inherently slower than a CPU TLB flush, so our design works by sending the invalidation request to the device, and waiting for an interrupt before exiting the mmu notifier handler. Avi said: kvm may be a buyer. kvm::mmu_lock, which serializes guest page faults, also protects long operations such as destroying large ranges. It would be good to convert it into a spinlock, but as it is used inside mmu notifiers, this cannot be done. (there are alternatives, such as keeping the spinlock and using a generation counter to do the teardown in O(1), which is what the "may" is doing up there). [akpm@linux-foundation.orgpossible speed tweak in hugetlb_cow(), cleanups] Signed-off-by: Andrea Arcangeli <andrea@qumranet.com> Signed-off-by: Sagi Grimberg <sagig@mellanox.com> Signed-off-by: Haggai Eran <haggaie@mellanox.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Cc: Or Gerlitz <ogerlitz@mellanox.com> Cc: Haggai Eran <haggaie@mellanox.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Liran Liss <liranl@mellanox.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/mmu_notifier.h47
1 files changed, 0 insertions, 47 deletions
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 4b7183e9806..bc823c4c028 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -246,50 +246,6 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
__mmu_notifier_mm_destroy(mm);
}
-/*
- * These two macros will sometime replace ptep_clear_flush.
- * ptep_clear_flush is implemented as macro itself, so this also is
- * implemented as a macro until ptep_clear_flush will converted to an
- * inline function, to diminish the risk of compilation failure. The
- * invalidate_page method over time can be moved outside the PT lock
- * and these two macros can be later removed.
- */
-#define ptep_clear_flush_notify(__vma, __address, __ptep) \
-({ \
- pte_t __pte; \
- struct vm_area_struct *___vma = __vma; \
- unsigned long ___address = __address; \
- __pte = ptep_clear_flush(___vma, ___address, __ptep); \
- mmu_notifier_invalidate_page(___vma->vm_mm, ___address); \
- __pte; \
-})
-
-#define pmdp_clear_flush_notify(__vma, __address, __pmdp) \
-({ \
- pmd_t __pmd; \
- struct vm_area_struct *___vma = __vma; \
- unsigned long ___address = __address; \
- VM_BUG_ON(__address & ~HPAGE_PMD_MASK); \
- mmu_notifier_invalidate_range_start(___vma->vm_mm, ___address, \
- (__address)+HPAGE_PMD_SIZE);\
- __pmd = pmdp_clear_flush(___vma, ___address, __pmdp); \
- mmu_notifier_invalidate_range_end(___vma->vm_mm, ___address, \
- (__address)+HPAGE_PMD_SIZE); \
- __pmd; \
-})
-
-#define pmdp_splitting_flush_notify(__vma, __address, __pmdp) \
-({ \
- struct vm_area_struct *___vma = __vma; \
- unsigned long ___address = __address; \
- VM_BUG_ON(__address & ~HPAGE_PMD_MASK); \
- mmu_notifier_invalidate_range_start(___vma->vm_mm, ___address, \
- (__address)+HPAGE_PMD_SIZE);\
- pmdp_splitting_flush(___vma, ___address, __pmdp); \
- mmu_notifier_invalidate_range_end(___vma->vm_mm, ___address, \
- (__address)+HPAGE_PMD_SIZE); \
-})
-
#define ptep_clear_flush_young_notify(__vma, __address, __ptep) \
({ \
int __young; \
@@ -380,9 +336,6 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
#define ptep_clear_flush_young_notify ptep_clear_flush_young
#define pmdp_clear_flush_young_notify pmdp_clear_flush_young
-#define ptep_clear_flush_notify ptep_clear_flush
-#define pmdp_clear_flush_notify pmdp_clear_flush
-#define pmdp_splitting_flush_notify pmdp_splitting_flush
#define set_pte_at_notify set_pte_at
#endif /* CONFIG_MMU_NOTIFIER */