[PATCH 11/23] thp, mm: handle tail pages in page_cache_get_speculative()
From: Kirill A. Shutemov <hidden>
Date: 2013-08-04 02:17:13
Also in:
linux-fsdevel, lkml
Subsystem:
page cache, the rest · Maintainers:
Matthew Wilcox, Linus Torvalds
From: "Kirill A. Shutemov" <redacted> For tail pages we need to take two refcounters: - ->_count for its head page; - ->_mapcount for the tail page; To protect against splitting we take compound lock and re-check that we still have tail page before taking ->_mapcount reference. If the page was split we drop ->_count reference from head page and return 0 to indicate caller that it must retry. Signed-off-by: Kirill A. Shutemov <redacted> --- include/linux/pagemap.h | 26 ++++++++++++++++++++++---- 1 file changed, 22 insertions(+), 4 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 47b5082..d459b38 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h@@ -161,6 +161,8 @@ void release_pages(struct page **pages, int nr, int cold); */ static inline int page_cache_get_speculative(struct page *page) { + struct page *page_head = compound_trans_head(page); + VM_BUG_ON(in_interrupt()); #ifdef CONFIG_TINY_RCU
@@ -176,11 +178,11 @@ static inline int page_cache_get_speculative(struct page *page) * disabling preempt, and hence no need for the "speculative get" that * SMP requires. */ - VM_BUG_ON(page_count(page) == 0); - atomic_inc(&page->_count); + VM_BUG_ON(page_count(page_head) == 0); + atomic_inc(&page_head->_count); #else - if (unlikely(!get_page_unless_zero(page))) { + if (unlikely(!get_page_unless_zero(page_head))) { /* * Either the page has been freed, or will be freed. * In either case, retry here and the caller should
@@ -189,7 +191,23 @@ static inline int page_cache_get_speculative(struct page *page) return 0; } #endif - VM_BUG_ON(PageTail(page)); + + if (unlikely(PageTransTail(page))) { + unsigned long flags; + int got = 0; + + flags = compound_lock_irqsave(page_head); + if (likely(PageTransTail(page))) { + atomic_inc(&page->_mapcount); + got = 1; + } + compound_unlock_irqrestore(page_head, flags); + + if (unlikely(!got)) + atomic_dec(&page_head->_count); + + return got; + } return 1; }
--
1.8.3.2
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