Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751639AbbDLLdV (ORCPT ); Sun, 12 Apr 2015 07:33:21 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:36080 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751522AbbDLLdQ (ORCPT ); Sun, 12 Apr 2015 07:33:16 -0400 Message-ID: <552A57F8.7020002@plexistor.com> Date: Sun, 12 Apr 2015 14:33:12 +0300 From: Boaz Harrosh User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Zhao Lei , "'Christoph Hellwig'" CC: linux-fsdevel@vger.kernel.org, "'Jan Kara'" , "'Jens Axboe'" , "'LKML'" Subject: Re: Regression caused by using node_to_bdi() References: <016d01d07380$fc37fc40$f4a7f4c0$@cn.fujitsu.com> In-Reply-To: <016d01d07380$fc37fc40$f4a7f4c0$@cn.fujitsu.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2828 Lines: 92 On 04/10/2015 02:25 PM, Zhao Lei wrote: > Hi, Christoph Hellwig > > resend: + cc lkml, linux-fsdevel > > Since there is no response for my last mail, I worry that some problem in > the mail system, please allow me to resend it. > > I found regression in v4.0-rc1 caused by this patch: > Author: Christoph Hellwig > Date: Wed Jan 14 10:42:36 2015 +0100 > fs: export inode_to_bdi and use it in favor of mapping->backing_dev_info > <> > Result is following: > v3.19-rc1: testcnt=40 average=135.677 range=[132.460,139.130] stdev=1.610 cv=1.19% > v4.0-rc1: testcnt=40 average=130.970 range=[127.980,132.050] stdev=1.012 cv=0.77% > > Then I bisect above case between v3.19-rc1 and v4.0-rc1, and found > this patch caused the regresstion. > > Maybe it is because kernel need more time to call node_to_bdi(), > compared with "using inode->i_mapping->backing_dev_info directly" in > old code. > > Is there some way to speed up it(inline, or some access some variant > in struct directly, ...)? > Christoph hi Both node_to_bdi() and sb_is_blkdev_sb() (and I_BDEV() && blk_get_backing_dev_info()) Are an exported function calls. Can we not make blockdev_superblock->s_bdi == NULL, and then optimize-out the call to sb_is_blkdev_sb() to only that case. Something like: --- diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 32a8bbd..e0375e1 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -78,7 +78,7 @@ int writeback_in_progress(struct backing_dev_info *bdi) } EXPORT_SYMBOL(writeback_in_progress); -struct backing_dev_info *inode_to_bdi(struct inode *inode) +struct backing_dev_info *__inode_to_bdi(struct inode *inode) { struct super_block *sb; @@ -92,7 +92,7 @@ struct backing_dev_info *inode_to_bdi(struct inode *inode) #endif return sb->s_bdi; } -EXPORT_SYMBOL_GPL(inode_to_bdi); +EXPORT_SYMBOL_GPL(__inode_to_bdi); static inline struct inode *wb_inode(struct list_head *head) { diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index aff923a..7d172f5 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -107,7 +107,16 @@ struct backing_dev_info { #endif }; -struct backing_dev_info *inode_to_bdi(struct inode *inode); +struct backing_dev_info *__inode_to_bdi(struct inode *inode); + +static inline +struct backing_dev_info *inode_to_bdi(struct inode *inode) +{ + if (!inode || !inode->i_sb) + return __inode_to_bdi(inode); + + return inode->i_sb->s_bdi; +} int __must_check bdi_init(struct backing_dev_info *bdi); void bdi_destroy(struct backing_dev_info *bdi); -- 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/