lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 9 Jan 2020 14:51:42 +0530 From: Ritesh Harjani <riteshh@...ux.ibm.com> To: "Theodore Y. Ts'o" <tytso@....edu> Cc: Jan Kara <jack@...e.cz>, Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>, Ext4 Developers List <linux-ext4@...r.kernel.org>, joseph.qi@...ux.alibaba.com, Liu Bo <bo.liu@...ux.alibaba.com> Subject: Re: Discussion: is it time to remove dioread_nolock? On 1/8/20 11:12 PM, Theodore Y. Ts'o wrote: > On Wed, Jan 08, 2020 at 04:15:13PM +0530, Ritesh Harjani wrote: >> Hello Ted/Jan, >> >> On 1/7/20 10:52 PM, Jan Kara wrote: >>> On Tue 07-01-20 12:11:09, Theodore Y. Ts'o wrote: >>>> Hmm..... There's actually an even more radical option we could use, >>>> given that Ritesh has made dioread_nolock work on block sizes < page >>>> size. We could make dioread_nolock the default, until we can revamp >>>> ext4_writepages() to write the data blocks first.... >> >> Agreed. I guess it should be a straight forward change to make. >> It should be just removing test_opt(inode->i_sb, DIOREAD_NOLOCK) condition >> from ext4_should_dioread_nolock(). > > Actually, it's simpler than that. In fs/ext4/super.c, around line > 3730, after the comment: > > /* Set defaults before we parse the mount options */ > > Just add: > > set_opt(sb, DIOREAD_NOLOCK); Yes, silly me. > > This will allow system administrators to revert back to the original > method using the someone confusingly named mount option, > "dioread_lock". (Maybe we can add a alias for that mount option so > it's less confusing). > >>> Yes, that's a good point. And I'm not opposed to that if it makes the life >>> simpler. But I'd like to see some performance numbers showing how much is >>> writeback using unwritten extents slower so that we don't introduce too big >>> regression with this... >>> >> >> Yes, let me try to get some performance numbers with dioread_nolock as >> the default option for buffered write on my setup. > > I started running some performance runs last night, and the > interesting thing that I found was that fs_mark actually *improved* > with dioread_nolock (with fsync enabled). That may be an example of > where fixing the commit latency caused by writeback can actually show > up in a measurable way with benchmarks. > > Dbench was slightly impacted; I didn't see any real differences with > compilebench or postmark. dioread_nolock did improve fio with > sequential reads; which is interesting, since I would have expected IIUC, this Seq. read numbers are with --direct=1 & bs=2MB & ioengine=libaio, correct? So essentially it will do a DIO AIO sequential read. Yes, it *does shows* a big delta in the numbers. I also noticed a higher deviation between the two runs with dioread_nolock. > with the inode_lock improvements, there shouldn't have been any > difference. So that may be a bit of wierdness that we should try to > understand. So inode_lock patches gives improvement in mixed read/write workload where inode exclusive locking was causing the bottleneck earlier. In this run, was encryption or fsverity enabled? If yes then in that case I see that ext4_dio_supported() will return false and it will fallback to bufferedRead. Though with that also can't explain the delta with only enabling dioread_nolock. > > See the attached tar file; open ext4-modes/index.html in a browser to > see the pretty graphs. The raw numbers are in ext4/composite.xml. The graphs and overview looks really good. I will also check about PTS sometime. Will be good to capture such reports. ritesh
Powered by blists - more mailing lists