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

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Date:   Tue, 1 Aug 2017 15:23:01 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        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 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.