[tip:,locking/core] futex: Use a folio instead of a page
Commit Message
The following commit has been merged into the locking/core branch of tip:
Commit-ID: e35a6cf1cc343d720ad235f678f1cd2a9876b777
Gitweb: https://git.kernel.org/tip/e35a6cf1cc343d720ad235f678f1cd2a9876b777
Author: Matthew Wilcox (Oracle) <willy@infradead.org>
AuthorDate: Mon, 21 Aug 2023 15:22:07 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 14 Sep 2023 00:03:09 +02:00
futex: Use a folio instead of a page
The futex code already handles compound pages correctly, but using a folio
tells the compiler that there is already a reference to the head page and
it doesn't need to call compound_head() again.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230821142207.2537124-1-willy@infradead.org
---
kernel/futex/core.c | 67 +++++++++++++++++++++-----------------------
1 file changed, 33 insertions(+), 34 deletions(-)
@@ -222,7 +222,8 @@ int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
- struct page *page, *tail;
+ struct page *page;
+ struct folio *folio;
struct address_space *mapping;
int err, ro = 0;
@@ -273,54 +274,52 @@ again:
err = 0;
/*
- * The treatment of mapping from this point on is critical. The page
- * lock protects many things but in this context the page lock
+ * The treatment of mapping from this point on is critical. The folio
+ * lock protects many things but in this context the folio lock
* stabilizes mapping, prevents inode freeing in the shared
* file-backed region case and guards against movement to swap cache.
*
- * Strictly speaking the page lock is not needed in all cases being
- * considered here and page lock forces unnecessarily serialization
+ * Strictly speaking the folio lock is not needed in all cases being
+ * considered here and folio lock forces unnecessarily serialization.
* From this point on, mapping will be re-verified if necessary and
- * page lock will be acquired only if it is unavoidable
+ * folio lock will be acquired only if it is unavoidable
*
- * Mapping checks require the head page for any compound page so the
- * head page and mapping is looked up now. For anonymous pages, it
- * does not matter if the page splits in the future as the key is
- * based on the address. For filesystem-backed pages, the tail is
- * required as the index of the page determines the key. For
- * base pages, there is no tail page and tail == page.
+ * Mapping checks require the folio so it is looked up now. For
+ * anonymous pages, it does not matter if the folio is split
+ * in the future as the key is based on the address. For
+ * filesystem-backed pages, the precise page is required as the
+ * index of the page determines the key.
*/
- tail = page;
- page = compound_head(page);
- mapping = READ_ONCE(page->mapping);
+ folio = page_folio(page);
+ mapping = READ_ONCE(folio->mapping);
/*
- * If page->mapping is NULL, then it cannot be a PageAnon
+ * If folio->mapping is NULL, then it cannot be an anonymous
* 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
* found it, but truncated or holepunched or subjected to
- * invalidate_complete_page2 before we got the page lock (also
+ * invalidate_complete_page2 before we got the folio lock (also
* cases which we are happy to fail). And we hold a reference,
* so refcount care in invalidate_inode_page's remove_mapping
* prevents drop_caches from setting mapping to NULL beneath us.
*
* 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->mapping.
+ * an unlikely race, but we do need to retry for folio->mapping.
*/
if (unlikely(!mapping)) {
int shmem_swizzled;
/*
- * Page lock is required to identify which special case above
- * applies. If this is really a shmem page then the page lock
+ * Folio lock is required to identify which special case above
+ * applies. If this is really a shmem page then the folio lock
* will prevent unexpected transitions.
*/
- lock_page(page);
- shmem_swizzled = PageSwapCache(page) || page->mapping;
- unlock_page(page);
- put_page(page);
+ folio_lock(folio);
+ shmem_swizzled = folio_test_swapcache(folio) || folio->mapping;
+ folio_unlock(folio);
+ folio_put(folio);
if (shmem_swizzled)
goto again;
@@ -331,14 +330,14 @@ again:
/*
* Private mappings are handled in a simple way.
*
- * If the futex key is stored on an anonymous page, then the associated
+ * If the futex key is stored in anonymous memory, then the associated
* object is the mm which is implicitly pinned by the calling process.
*
* NOTE: When userspace waits on a MAP_SHARED mapping, even if
* it's a read-only handle, it's expected that futexes attach to
* the object not the particular process.
*/
- if (PageAnon(page)) {
+ if (folio_test_anon(folio)) {
/*
* A RO anonymous page will never change and thus doesn't make
* sense for futex operations.
@@ -357,10 +356,10 @@ again:
/*
* The associated futex object in this case is the inode and
- * the page->mapping must be traversed. Ordinarily this should
- * be stabilised under page lock but it's not strictly
+ * the folio->mapping must be traversed. Ordinarily this should
+ * be stabilised under folio lock but it's not strictly
* necessary in this case as we just want to pin the inode, not
- * update the radix tree or anything like that.
+ * update i_pages or anything like that.
*
* The RCU read lock is taken as the inode is finally freed
* under RCU. If the mapping still matches expectations then the
@@ -368,9 +367,9 @@ again:
*/
rcu_read_lock();
- if (READ_ONCE(page->mapping) != mapping) {
+ if (READ_ONCE(folio->mapping) != mapping) {
rcu_read_unlock();
- put_page(page);
+ folio_put(folio);
goto again;
}
@@ -378,19 +377,19 @@ again:
inode = READ_ONCE(mapping->host);
if (!inode) {
rcu_read_unlock();
- put_page(page);
+ folio_put(folio);
goto again;
}
key->both.offset |= FUT_OFF_INODE; /* inode-based key */
key->shared.i_seq = get_inode_sequence_number(inode);
- key->shared.pgoff = page_to_pgoff(tail);
+ key->shared.pgoff = folio->index + folio_page_idx(folio, page);
rcu_read_unlock();
}
out:
- put_page(page);
+ folio_put(folio);
return err;
}