linux-kernel - Re: [RFC] mm: remove swapcache page early

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Date:	Wed, 27 Mar 2013 14:15:41 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Shaohua Li <shli@...nel.org>
Subject: Re: [RFC] mm: remove swapcache page early

(2013/03/27 11:22), Minchan Kim wrote:
> Swap subsystem does lazy swap slot free with expecting the page
> would be swapped out again so we can't avoid unnecessary write.
> 
> But the problem in in-memory swap is that it consumes memory space
> until vm_swap_full(ie, used half of all of swap device) condition
> meet. It could be bad if we use multiple swap device, small in-memory swap
> and big storage swap or in-memory swap alone.
> 
> This patch changes vm_swap_full logic slightly so it could free
> swap slot early if the backed device is really fast.
> For it, I used SWP_SOLIDSTATE but It might be controversial.
> So let's add Ccing Shaohua and Hugh.
> If it's a problem for SSD, I'd like to create new type SWP_INMEMORY
> or something for z* family.
> 
> Other problem is zram is block device so that it can set SWP_INMEMORY
> or SWP_SOLIDSTATE easily(ie, actually, zram is already done) but
> I have no idea to use it for frontswap.
> 
> Any idea?
> 
Another thinking....in what case, in what system configuration, 
vm_swap_full() should return false and delay swp_entry freeing ?

Thanks,
-Kame


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