From: Theodore Ts'o Subject: Re: [PATCH v3 3/6] ext4: cache extent hole in extent status tree for ext4_da_map_blocks() Date: Mon, 1 Sep 2014 22:43:50 -0400 Message-ID: <20140902024350.GS8974@thunk.org> References: <1407382553-24256-1-git-send-email-wenqing.lz@taobao.com> <1407382553-24256-4-git-send-email-wenqing.lz@taobao.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, Andreas Dilger , Jan Kara , Zheng Liu To: Zheng Liu Return-path: Received: from imap.thunk.org ([74.207.234.97]:60029 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751436AbaIBCn6 (ORCPT ); Mon, 1 Sep 2014 22:43:58 -0400 Content-Disposition: inline In-Reply-To: <1407382553-24256-4-git-send-email-wenqing.lz@taobao.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Aug 07, 2014 at 11:35:50AM +0800, Zheng Liu wrote: > From: Zheng Liu > > Currently extent status tree doesn't cache extent hole when a write > looks up in extent tree to make sure whether a block has been allocated > or not. In this case, we don't put extent hole in extent cache because > later this extent might be removed and a new delayed extent might be > added back. But it will cause a defect when we do a lot of writes. > If we don't put extent hole in extent cache, the following writes also > need to access extent tree to look at whether or not a block has been > allocated. It brings a cache miss. This commit fixes this defect. > Meanwhile, if an inode has no any extent, this extent hole also will > be cached. Hi Zheng, I thought the reason why we have the EXT4_GET_BLOCKS_NO_PUT_HOLE flag is because in ext4_da_map_blocks(), if there is a hole, we will be immediately following it up with a call to ext4_es_insert_extent() to fill in the hole with the EXTENT_STATUS_DELAYED flag. The only time we don't is if we run into an ENOSPC error. Am I missing something? - Ted