From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 1B54D6B004D for ; Wed, 27 May 2009 03:40:18 -0400 (EDT) Received: by pxi37 with SMTP id 37so4715423pxi.12 for ; Wed, 27 May 2009 00:40:56 -0700 (PDT) Message-ID: <4A1CEE3F.6030504@gmail.com> Date: Wed, 27 May 2009 15:39:43 +0800 From: Huang Shijie MIME-Version: 1.0 Subject: Re: [PATCH] lib : provide a more precise radix_tree_gang_lookup_slot References: <1243223635-3449-1-git-send-email-shijie8@gmail.com> <20090526143058.c59e6dc1.akpm@linux-foundation.org> In-Reply-To: <20090526143058.c59e6dc1.akpm@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: cl@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: >> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h >> index 355f6e8..03e25f4 100644 >> --- a/include/linux/radix-tree.h >> +++ b/include/linux/radix-tree.h >> @@ -164,7 +164,8 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results, >> unsigned long first_index, unsigned int max_items); >> unsigned int >> radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, >> - unsigned long first_index, unsigned int max_items); >> + unsigned long first_index, unsigned int max_items, >> + int contig); >> > > Variable `contig' could have the type `bool'. Did you consider and > reject that option, or just didn't think of it? > > > Yes, type `bool' is better. >> ... >> + if (contig) >> + goto out; >> + >> + } else if (contig) { >> + index--; >> + goto out; >> + >> + if (contig) { >> + if (slots_found == 0) >> + break; >> + if (next_index & RADIX_TREE_MAP_MASK) >> + break; >> + } >> - (void ***)pages, start, nr_pages); >> + (void ***)pages, start, nr_pages, 0); >> - (void ***)pages, index, nr_pages); >> + (void ***)pages, index, nr_pages, 1); >> > > The patch adds cycles in some cases and saves them in others. > > Does the saving exceed the adding? How do we know that the patch is a > net benefit? > > Assume that: f0 = called frequency of find_get_pages() (contig == 0) f1 = called frequency of find_get_pages_contig() (contig == 1) The primary user of find_get_pages() is ->writepage[s] of some file systems such as ext4. ( I think the shmem_lock() ,truncate() run occasionally which also call it.) The primary user of find_get_pages_contig() is also the ->writepage[s] of some filesystem such as afs.( I am not sure whether btrfs is also the main user of it ) So if (f0 nearly equal f1) cycles saving >> cycles adding __lookup() saves much cycles when there are holes and the contig==1. -- 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