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Diffstat (limited to 'Documentation/mm/split_page_table_lock.rst')
| -rw-r--r-- | Documentation/mm/split_page_table_lock.rst | 35 |
1 files changed, 22 insertions, 13 deletions
diff --git a/Documentation/mm/split_page_table_lock.rst b/Documentation/mm/split_page_table_lock.rst index 50ee0dfc95be..cc3cd46abd1b 100644 --- a/Documentation/mm/split_page_table_lock.rst +++ b/Documentation/mm/split_page_table_lock.rst @@ -4,7 +4,7 @@ Split page table lock Originally, mm->page_table_lock spinlock protected all page tables of the mm_struct. But this approach leads to poor page fault scalability of -multi-threaded applications due high contention on the lock. To improve +multi-threaded applications due to high contention on the lock. To improve scalability, split page table lock was introduced. With split page table lock we have separate per-table lock to serialize @@ -14,15 +14,24 @@ tables. Access to higher level tables protected by mm->page_table_lock. There are helpers to lock/unlock a table and other accessor functions: - pte_offset_map_lock() - maps pte and takes PTE table lock, returns pointer to the taken - lock; + maps PTE and takes PTE table lock, returns pointer to PTE with + pointer to its PTE table lock, or returns NULL if no PTE table; + - pte_offset_map_ro_nolock() + maps PTE, returns pointer to PTE with pointer to its PTE table + lock (not taken), or returns NULL if no PTE table; + - pte_offset_map_rw_nolock() + maps PTE, returns pointer to PTE with pointer to its PTE table + lock (not taken) and the value of its pmd entry, or returns NULL + if no PTE table; + - pte_offset_map() + maps PTE, returns pointer to PTE, or returns NULL if no PTE table; + - pte_unmap() + unmaps PTE table; - pte_unmap_unlock() unlocks and unmaps PTE table; - pte_alloc_map_lock() - allocates PTE table if needed and take the lock, returns pointer - to taken lock or NULL if allocation failed; - - pte_lockptr() - returns pointer to PTE table lock; + allocates PTE table if needed and takes its lock, returns pointer to + PTE with pointer to its lock, or returns NULL if allocation failed; - pmd_lock() takes PMD table lock, returns pointer to taken lock; - pmd_lockptr() @@ -53,7 +62,7 @@ Support of split page table lock by an architecture =================================================== There's no need in special enabling of PTE split page table lock: everything -required is done by pgtable_pte_page_ctor() and pgtable_pte_page_dtor(), which +required is done by pagetable_pte_ctor() and pagetable_dtor(), which must be called on PTE table allocation / freeing. Make sure the architecture doesn't use slab allocator for page table @@ -63,8 +72,8 @@ This field shares storage with page->ptl. PMD split lock only makes sense if you have more than two page table levels. -PMD split lock enabling requires pgtable_pmd_page_ctor() call on PMD table -allocation and pgtable_pmd_page_dtor() on freeing. +PMD split lock enabling requires pagetable_pmd_ctor() call on PMD table +allocation and pagetable_dtor() on freeing. Allocation usually happens in pmd_alloc_one(), freeing in pmd_free() and pmd_free_tlb(), but make sure you cover all PMD table allocation / freeing @@ -72,7 +81,7 @@ paths: i.e X86_PAE preallocate few PMDs on pgd_alloc(). With everything in place you can set CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK. -NOTE: pgtable_pte_page_ctor() and pgtable_pmd_page_ctor() can fail -- it must +NOTE: pagetable_pte_ctor() and pagetable_pmd_ctor() can fail -- it must be handled properly. page->ptl @@ -92,7 +101,7 @@ trick: split lock with enabled DEBUG_SPINLOCK or DEBUG_LOCK_ALLOC, but costs one more cache line for indirect access; -The spinlock_t allocated in pgtable_pte_page_ctor() for PTE table and in -pgtable_pmd_page_ctor() for PMD table. +The spinlock_t allocated in pagetable_pte_ctor() for PTE table and in +pagetable_pmd_ctor() for PMD table. Please, never access page->ptl directly -- use appropriate helper. |