Date: Tue, 1 Aug 2017 15:23:01 +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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 <20170731074206.GA16706@lst.de>
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On Mon, Jul 31, 2017 at 09:44:04AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 31, 2017 at 09:42:06AM +0200, Christoph Hellwig wrote:
> > On Mon, Jul 31, 2017 at 04:36:47PM +0900, Minchan Kim wrote:
> > > 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?
> > 
> > Currently swap always just does I/O on a single page as far
> > as I can tell, so it can always just use an on-stack bio and
> > biovec.
> 
> That's for synchronous I/O, aka reads of course.  For writes you'll
> need to do a dynamic allocation if they are asynchronous.  But yes,
> if we want to force certain devices to be synchronous we'll need
> a flag for that.

Okay, I will look into that.
Thanks for the suggestion, Christoph.