Date: Mon, 31 Jul 2017 16:36:47 +0900
From: Minchan Kim <minchan@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        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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References: <20170728165604.10455-1-ross.zwisler@linux.intel.com>
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 <20170728142123.729b20e9fcf45c6a814f18e7@linux-foundation.org>
 <20170730221659.GA28031@bbox>
 <20170731071707.GA16299@lst.de>
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On Mon, Jul 31, 2017 at 09:17:07AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 31, 2017 at 07:16:59AM +0900, Minchan Kim wrote:
> > rw_page's gain is reducing of dynamic allocation in swap path
> > as well as performance gain thorugh avoiding bio allocation.
> > And it would be important in memory pressure situation.
> 
> There is no need for any dynamic allocation when using the bio
> path.  Take a look at __blkdev_direct_IO_simple for an example
> that doesn't do any allocations.

Do you suggest define something special flag(e.g., SWP_INMEMORY)
for in-memory swap to swap_info_struct when swapon time manually
or from bdi_queue_someting automatically?
And depending the flag of swap_info_struct, use the onstack bio
instead of dynamic allocation if the swap device is in-memory?