Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754294AbaBDBAq (ORCPT ); Mon, 3 Feb 2014 20:00:46 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:56943 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753774AbaBDA6k (ORCPT ); Mon, 3 Feb 2014 19:58:40 -0500 From: Johannes Weiner To: Andrew Morton Cc: Andi Kleen , Andrea Arcangeli , Bob Liu , Christoph Hellwig , Dave Chinner , Greg Thelen , Hugh Dickins , Jan Kara , KOSAKI Motohiro , Luigi Semenzato , Mel Gorman , Metin Doslu , Michel Lespinasse , Minchan Kim , Ozgun Erdogan , Peter Zijlstra , Rik van Riel , Roman Gushchin , Ryan Mallon , Tejun Heo , Vlastimil Babka , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [patch 04/10] mm: shmem: save one radix tree lookup when truncating swapped pages Date: Mon, 3 Feb 2014 19:53:36 -0500 Message-Id: <1391475222-1169-5-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 1.8.5.3 In-Reply-To: <1391475222-1169-1-git-send-email-hannes@cmpxchg.org> References: <1391475222-1169-1-git-send-email-hannes@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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 Reviewed-by: Minchan Kim Reviewed-by: Rik van Riel --- mm/shmem.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 1f18c9d0d93e..e470997010cd 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; } /* -- 1.8.5.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/