On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
With new THP refcounting, we don't need tricks to stabilize huge page.
If we've got reference to tail page, it can't split under us.
This patch effectively reverts a5b338f2b0b1.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
kernel/futex.c | 61 ++++++++++++----------------------------------------------
1 file changed, 12 insertions(+), 49 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index f4d8a85641ed..cf0192e60ef9 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -399,7 +399,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
- struct page *page, *page_head;
+ struct page *page;
int err, ro = 0;
/*
@@ -442,46 +442,9 @@ again:
else
err = 0;
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- page_head = page;
- if (unlikely(PageTail(page))) {
- put_page(page);
- /* serialize against __split_huge_page_splitting() */
- local_irq_disable();
- if (likely(__get_user_pages_fast(address, 1, !ro, &page) == 1)) {
- page_head = compound_head(page);
- /*
- * page_head is valid pointer but we must pin
- * it before taking the PG_lock and/or
- * PG_compound_lock. The moment we re-enable
- * irqs __split_huge_page_splitting() can
- * return and the head page can be freed from
- * under us. We can't take the PG_lock and/or
- * PG_compound_lock on a page that could be
- * freed from under us.
- */
- if (page != page_head) {
- get_page(page_head);
- put_page(page);
- }
- local_irq_enable();
- } else {
- local_irq_enable();
- goto again;
- }
- }
-#else
- page_head = compound_head(page);
- if (page != page_head) {
- get_page(page_head);
- put_page(page);
- }
Hmm, any idea why this was there? Without THP, it was already sure that
get/put_page() on tail page operates on the head page's _count, no?
-#endif
-
- lock_page(page_head);
-
+ lock_page(page);
/*
- * If page_head->mapping is NULL, then it cannot be a PageAnon
+ * If page->mapping is NULL, then it cannot be a PageAnon
* page; but it might be the ZERO_PAGE or in the gate area or
* in a special mapping (all cases which we are happy to fail);
* or it may have been a good file page when get_user_pages_fast
@@ -493,12 +456,12 @@ again:
*
* The case we do have to guard against is when memory pressure made
* shmem_writepage move it from filecache to swapcache beneath us:
- * an unlikely race, but we do need to retry for page_head->mapping.
+ * an unlikely race, but we do need to retry for page->mapping.
*/
- if (!page_head->mapping) {
- int shmem_swizzled = PageSwapCache(page_head);
- unlock_page(page_head);
- put_page(page_head);
+ if (!page->mapping) {
+ int shmem_swizzled = PageSwapCache(page);
+ unlock_page(page);
+ put_page(page);
if (shmem_swizzled)
goto again;
return -EFAULT;
@@ -511,7 +474,7 @@ again:
* it's a read-only handle, it's expected that futexes attach to
* the object not the particular process.
*/
- if (PageAnon(page_head)) {
+ if (PageAnon(page)) {
/*
* A RO anonymous page will never change and thus doesn't make
* sense for futex operations.
@@ -526,15 +489,15 @@ again:
key->private.address = address;
} else {
key->both.offset |= FUT_OFF_INODE; /* inode-based key */
- key->shared.inode = page_head->mapping->host;
+ key->shared.inode = page->mapping->host;
key->shared.pgoff = basepage_index(page);
}
get_futex_key_refs(key); /* implies MB (B) */
out:
- unlock_page(page_head);
- put_page(page_head);
+ unlock_page(page);
+ put_page(page);
return err;
}
--
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