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Date: Wed, 8 Jan 2020 16:15:13 +0530 From: Ritesh Harjani <riteshh@...ux.ibm.com> To: Jan Kara <jack@...e.cz>, "Theodore Y. Ts'o" <tytso@....edu> Cc: 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? 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(). > > 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. AFAIU this should also fix the stale data exposure race between DIO read and ext4_page_mkwrite, since we will by default be using unwritten extents. Currently I am testing the patch to fix this race which is based on our previous discussion. Will anyway post that. After that I can also collect the performance numbers for this suggested option (to make dioread_nolock as default) -ritesh
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