Date: Fri, 4 Aug 2017 09:57:49 +0900
From: Minchan Kim <minchan@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, "karam . lee" <karam.lee@lge.com>,
        Jerome Marchand <jmarchan@redhat.com>, Nitin Gupta <ngupta@vflare.org>,
        seungho1.park@lge.com, Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>,
        Jens Axboe <axboe@kernel.dk>, Vishal Verma <vishal.l.verma@intel.com>,
        linux-nvdimm@lists.01.org
Subject: Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt
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 <20170802221359.GA20666@linux.intel.com>
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On Thu, Aug 03, 2017 at 10:05:44AM +0200, Christoph Hellwig wrote:
> FYI, for the read side we should use the on-stack bio unconditionally,
> as it will always be a win (or not show up at all).

Think about readahead. Unconditional on-stack bio to read around pages
with faulted address will cause latency peek. So, I want to use that
synchronous IO only if device says "Hey, I'm a synchronous".