From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chao Yu Subject: Re: [PATCH v2] f2fs: merge two uchar variable in struct node_info to reduce memory cost Date: Thu, 18 Dec 2014 14:29:51 +0800 Message-ID: <004c01d01a96$2b5b3a80$8211af80$@samsung.com> References: <000001d0184a$3f09d580$bd1d8080$@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: 'Jaegeuk Kim' , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net To: 'Changman Lee' Return-path: In-reply-to: Content-language: zh-cn List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net List-Id: linux-fsdevel.vger.kernel.org Hi Changman, > -----Original Message----- > From: Changman Lee [mailto:cm224.lee@gmail.com] > Sent: Wednesday, December 17, 2014 11:09 PM > To: Chao Yu > Cc: Jaegeuk Kim; Changman Lee; linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; > linux-f2fs-devel@lists.sourceforge.net > Subject: Re: [f2fs-dev] [PATCH v2] f2fs: merge two uchar variable in struct node_info to reduce > memory cost > > Hi Yu, > > This patch is effective only in 32 bit machine. In case of 64 bit > machine, nat_entry will be aligned in 8 bytes due to pointer variable > (i.e. struct list_head). So it can't get any benefit to reduce memory > usage. In the case of node_info, however, it will be gain in terms of > memory usage. > Hence, I think it's not correct for commit log to describe this patch. > Thanks for your review! :) AFFIK, in 64 bit machine, size of struct nat_entry is 40 bytes before this patch apply, the reason is that our compiler will fill 3 bytes pads after flag as nid's offset should align to type size of nid, and then fill 7 byte pads after version as size of structure should align to 64 bits when the struct size is bigger than 64 bits. layout of struct nat_entry: |-----8 bytes-----| |list.next | |list.prev | |flag |nid | |ino |blk_addr| |version | After we apply this patch, size of struct nat_entry will be reduced to 32 bytes. Please correct me if I'm wrong. Anyway, I agreed that commit log should be uptodate. Thanks, Yu > Thanks, > > Reviewed-by: Changman Lee > ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk