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authorHugh Dickins <hugh@veritas.com>2005-10-29 18:16:40 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-29 21:40:42 -0700
commit4c21e2f2441dc5fbb957b030333f5a3f2d02dea7 (patch)
tree1f76d33bb1d76221c6424bc5fed080a4f91349a6 /mm/memory.c
parentb38c6845b695141259019e2b7c0fe6c32a6e720d (diff)
[PATCH] mm: split page table lock
Christoph Lameter demonstrated very poor scalability on the SGI 512-way, with a many-threaded application which concurrently initializes different parts of a large anonymous area. This patch corrects that, by using a separate spinlock per page table page, to guard the page table entries in that page, instead of using the mm's single page_table_lock. (But even then, page_table_lock is still used to guard page table allocation, and anon_vma allocation.) In this implementation, the spinlock is tucked inside the struct page of the page table page: with a BUILD_BUG_ON in case it overflows - which it would in the case of 32-bit PA-RISC with spinlock debugging enabled. Splitting the lock is not quite for free: another cacheline access. Ideally, I suppose we would use split ptlock only for multi-threaded processes on multi-cpu machines; but deciding that dynamically would have its own costs. So for now enable it by config, at some number of cpus - since the Kconfig language doesn't support inequalities, let preprocessor compare that with NR_CPUS. But I don't think it's worth being user-configurable: for good testing of both split and unsplit configs, split now at 4 cpus, and perhaps change that to 8 later. There is a benefit even for singly threaded processes: kswapd can be attacking one part of the mm while another part is busy faulting. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c24
1 files changed, 14 insertions, 10 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 8461e2dd91d..e9ef599498b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -114,6 +114,7 @@ static void free_pte_range(struct mmu_gather *tlb, pmd_t *pmd)
{
struct page *page = pmd_page(*pmd);
pmd_clear(pmd);
+ pte_lock_deinit(page);
pte_free_tlb(tlb, page);
dec_page_state(nr_page_table_pages);
tlb->mm->nr_ptes--;
@@ -294,10 +295,12 @@ int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
if (!new)
return -ENOMEM;
+ pte_lock_init(new);
spin_lock(&mm->page_table_lock);
- if (pmd_present(*pmd)) /* Another has populated it */
+ if (pmd_present(*pmd)) { /* Another has populated it */
+ pte_lock_deinit(new);
pte_free(new);
- else {
+ } else {
mm->nr_ptes++;
inc_page_state(nr_page_table_pages);
pmd_populate(mm, pmd, new);
@@ -432,7 +435,7 @@ again:
if (!dst_pte)
return -ENOMEM;
src_pte = pte_offset_map_nested(src_pmd, addr);
- src_ptl = &src_mm->page_table_lock;
+ src_ptl = pte_lockptr(src_mm, src_pmd);
spin_lock(src_ptl);
do {
@@ -1194,15 +1197,16 @@ EXPORT_SYMBOL(remap_pfn_range);
* (but do_wp_page is only called after already making such a check;
* and do_anonymous_page and do_no_page can safely check later on).
*/
-static inline int pte_unmap_same(struct mm_struct *mm,
+static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
pte_t *page_table, pte_t orig_pte)
{
int same = 1;
#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
if (sizeof(pte_t) > sizeof(unsigned long)) {
- spin_lock(&mm->page_table_lock);
+ spinlock_t *ptl = pte_lockptr(mm, pmd);
+ spin_lock(ptl);
same = pte_same(*page_table, orig_pte);
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(ptl);
}
#endif
pte_unmap(page_table);
@@ -1655,7 +1659,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
pte_t pte;
int ret = VM_FAULT_MINOR;
- if (!pte_unmap_same(mm, page_table, orig_pte))
+ if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
goto out;
entry = pte_to_swp_entry(orig_pte);
@@ -1773,7 +1777,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
page_cache_get(page);
entry = mk_pte(page, vma->vm_page_prot);
- ptl = &mm->page_table_lock;
+ ptl = pte_lockptr(mm, pmd);
spin_lock(ptl);
if (!pte_none(*page_table))
goto release;
@@ -1934,7 +1938,7 @@ static int do_file_page(struct mm_struct *mm, struct vm_area_struct *vma,
pgoff_t pgoff;
int err;
- if (!pte_unmap_same(mm, page_table, orig_pte))
+ if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
return VM_FAULT_MINOR;
if (unlikely(!(vma->vm_flags & VM_NONLINEAR))) {
@@ -1992,7 +1996,7 @@ static inline int handle_pte_fault(struct mm_struct *mm,
pte, pmd, write_access, entry);
}
- ptl = &mm->page_table_lock;
+ ptl = pte_lockptr(mm, pmd);
spin_lock(ptl);
if (unlikely(!pte_same(*pte, entry)))
goto unlock;