From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: [patch 3/9] mm: shmem: save one radix tree lookup when truncating swapped pages Date: Sun, 24 Nov 2013 18:38:22 -0500 Message-ID: <1385336308-27121-4-git-send-email-hannes@cmpxchg.org> References: <1385336308-27121-1-git-send-email-hannes@cmpxchg.org> Cc: Dave Chinner , Rik van Riel , Jan Kara , Vlastimil Babka , Peter Zijlstra , Tejun Heo , Andi Kleen , Andrea Arcangeli , Greg Thelen , Christoph Hellwig , Hugh Dickins , KOSAKI Motohiro , Mel Gorman , Minchan Kim , Michel Lespinasse , Seth Jennings , Roman Gushchin , Ozgun Erdogan , Metin Doslu , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Andrew Morton Return-path: In-Reply-To: <1385336308-27121-1-git-send-email-hannes@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org Page cache radix tree slots are usually stabilized by the page lock, but shmem's swap cookies have no such thing. Because the overall truncation loop is lockless, the swap entry is currently confirmed by a tree lookup and then deleted by another tree lookup under the same tree lock region. Use radix_tree_delete_item() instead, which does the verification and deletion with only one lookup. This also allows removing the delete-only special case from shmem_radix_tree_replace(). Signed-off-by: Johannes Weiner --- mm/shmem.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 8297623..7c67249 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -242,19 +242,17 @@ static int shmem_radix_tree_replace(struct address_space *mapping, pgoff_t index, void *expected, void *replacement) { void **pslot; - void *item = NULL; + void *item; VM_BUG_ON(!expected); + VM_BUG_ON(!replacement); pslot = radix_tree_lookup_slot(&mapping->page_tree, index); - if (pslot) - item = radix_tree_deref_slot_protected(pslot, - &mapping->tree_lock); + if (!pslot) + return -ENOENT; + item = radix_tree_deref_slot_protected(pslot, &mapping->tree_lock); if (item != expected) return -ENOENT; - if (replacement) - radix_tree_replace_slot(pslot, replacement); - else - radix_tree_delete(&mapping->page_tree, index); + radix_tree_replace_slot(pslot, replacement); return 0; } @@ -386,14 +384,15 @@ export: static int shmem_free_swap(struct address_space *mapping, pgoff_t index, void *radswap) { - int error; + void *old; spin_lock_irq(&mapping->tree_lock); - error = shmem_radix_tree_replace(mapping, index, radswap, NULL); + old = radix_tree_delete_item(&mapping->page_tree, index, radswap); spin_unlock_irq(&mapping->tree_lock); - if (!error) - free_swap_and_cache(radix_to_swp_entry(radswap)); - return error; + if (old != radswap) + return -ENOENT; + free_swap_and_cache(radix_to_swp_entry(radswap)); + return 0; } /* -- 1.8.4.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org