linux-kernel - Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt

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Message-ID: <20170804005749.GA8368@bbox>
Date:   Fri, 4 Aug 2017 09:57:49 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, "karam . lee" <karam.lee@....com>,
        Jerome Marchand <jmarchan@...hat.com>,
        Nitin Gupta <ngupta@...are.org>, seungho1.park@....com,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
        Jens Axboe <axboe@...nel.dk>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-nvdimm@...ts.01.org
Subject: Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt

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".