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Diffstat (limited to 'Documentation/mm/hmm.rst')
| -rw-r--r-- | Documentation/mm/hmm.rst | 25 |
1 files changed, 8 insertions, 17 deletions
diff --git a/Documentation/mm/hmm.rst b/Documentation/mm/hmm.rst index 9aa512c3a12c..7d61b7a8b65b 100644 --- a/Documentation/mm/hmm.rst +++ b/Documentation/mm/hmm.rst @@ -66,7 +66,7 @@ combinatorial explosion in the library entry points. Finally, with the advance of high level language constructs (in C++ but in other languages too) it is now possible for the compiler to leverage GPUs and other devices without programmer knowledge. Some compiler identified patterns -are only do-able with a shared address space. It is also more reasonable to use +are only doable with a shared address space. It is also more reasonable to use a shared address space for all other patterns. @@ -163,16 +163,7 @@ use:: It will trigger a page fault on missing or read-only entries if write access is requested (see below). Page faults use the generic mm page fault code path just -like a CPU page fault. - -Both functions copy CPU page table entries into their pfns array argument. Each -entry in that array corresponds to an address in the virtual range. HMM -provides a set of flags to help the driver identify special CPU page table -entries. - -Locking within the sync_cpu_device_pagetables() callback is the most important -aspect the driver must respect in order to keep things properly synchronized. -The usage pattern is:: +like a CPU page fault. The usage pattern is:: int driver_populate_range(...) { @@ -276,7 +267,7 @@ functions are designed to make drivers easier to write and to centralize common code across drivers. Before migrating pages to device private memory, special device private -``struct page`` need to be created. These will be used as special "swap" +``struct page`` needs to be created. These will be used as special "swap" page table entries so that a CPU process will fault if it tries to access a page that has been migrated to device private memory. @@ -331,7 +322,7 @@ between device driver specific code and shared common code: The ``invalidate_range_start()`` callback is passed a ``struct mmu_notifier_range`` with the ``event`` field set to ``MMU_NOTIFY_MIGRATE`` and the ``owner`` field set to - the ``args->pgmap_owner`` field passed to migrate_vma_setup(). This is + the ``args->pgmap_owner`` field passed to migrate_vma_setup(). This allows the device driver to skip the invalidation callback and only invalidate device private MMU mappings that are actually migrating. This is explained more in the next section. @@ -409,15 +400,15 @@ Exclusive access memory Some devices have features such as atomic PTE bits that can be used to implement atomic access to system memory. To support atomic operations to a shared virtual memory page such a device needs access to that page which is exclusive of any -userspace access from the CPU. The ``make_device_exclusive_range()`` function +userspace access from the CPU. The ``make_device_exclusive()`` function can be used to make a memory range inaccessible from userspace. This replaces all mappings for pages in the given range with special swap entries. Any attempt to access the swap entry results in a fault which is -resovled by replacing the entry with the original mapping. A driver gets +resolved by replacing the entry with the original mapping. A driver gets notified that the mapping has been changed by MMU notifiers, after which point it will no longer have exclusive access to the page. Exclusive access is -guranteed to last until the driver drops the page lock and page reference, at +guaranteed to last until the driver drops the page lock and page reference, at which point any CPU faults on the page may proceed as described. Memory cgroup (memcg) and rss accounting @@ -440,7 +431,7 @@ Same decision was made for memory cgroup. Device memory pages are accounted against same memory cgroup a regular page would be accounted to. This does simplify migration to and from device memory. This also means that migration back from device memory to regular memory cannot fail because it would -go above memory cgroup limit. We might revisit this choice latter on once we +go above memory cgroup limit. We might revisit this choice later on once we get more experience in how device memory is used and its impact on memory resource control. |