path: root/mm/memory.c
diff options
authorSagi Grimberg <>2012-10-08 16:33:33 -0700
committerLinus Torvalds <>2012-10-09 16:22:58 +0900
commit2ec74c3ef2d8c58d71e0e00336fb6b891192155a (patch)
tree512b591504cdbee278c27afc50a7e3a558b4851a /mm/memory.c
parent36e4f20af833d1ce196e6a4ade05dc26c44652d1 (diff)
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 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 <> Signed-off-by: Sagi Grimberg <> Signed-off-by: Haggai Eran <> Cc: Peter Zijlstra <> Cc: Xiao Guangrong <> Cc: Or Gerlitz <> Cc: Haggai Eran <> Cc: Shachar Raindel <> Cc: Liran Liss <> Cc: Christoph Lameter <> Cc: Avi Kivity <> Cc: Hugh Dickins <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/memory.c')
1 files changed, 19 insertions, 9 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 5f5d1f039bf4..b03a4a21c1d0 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -712,7 +712,7 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
-static inline int is_cow_mapping(vm_flags_t flags)
+static inline bool is_cow_mapping(vm_flags_t flags)
return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
@@ -1039,6 +1039,9 @@ int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
unsigned long next;
unsigned long addr = vma->vm_start;
unsigned long end = vma->vm_end;
+ unsigned long mmun_start; /* For mmu_notifiers */
+ unsigned long mmun_end; /* For mmu_notifiers */
+ bool is_cow;
int ret;
@@ -1072,8 +1075,12 @@ int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* parent mm. And a permission downgrade will only happen if
* is_cow_mapping() returns true.
- if (is_cow_mapping(vma->vm_flags))
- mmu_notifier_invalidate_range_start(src_mm, addr, end);
+ is_cow = is_cow_mapping(vma->vm_flags);
+ mmun_start = addr;
+ mmun_end = end;
+ if (is_cow)
+ mmu_notifier_invalidate_range_start(src_mm, mmun_start,
+ mmun_end);
ret = 0;
dst_pgd = pgd_offset(dst_mm, addr);
@@ -1089,9 +1096,8 @@ int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
} while (dst_pgd++, src_pgd++, addr = next, addr != end);
- if (is_cow_mapping(vma->vm_flags))
- mmu_notifier_invalidate_range_end(src_mm,
- vma->vm_start, end);
+ if (is_cow)
+ mmu_notifier_invalidate_range_end(src_mm, mmun_start, mmun_end);
return ret;
@@ -2516,7 +2522,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
spinlock_t *ptl, pte_t orig_pte)
- struct page *old_page, *new_page;
+ struct page *old_page, *new_page = NULL;
pte_t entry;
int ret = 0;
int page_mkwrite = 0;
@@ -2760,10 +2766,14 @@ gotten:
} else
- if (new_page)
- page_cache_release(new_page);
pte_unmap_unlock(page_table, ptl);
+ if (new_page) {
+ if (new_page == old_page)
+ /* cow happened, notify before releasing old_page */
+ mmu_notifier_invalidate_page(mm, address);
+ page_cache_release(new_page);
+ }
if (old_page) {
* Don't let another task, with possibly unlocked vma,