linux-kernel - Re: [PATCH][RF C/T/D] Unmapped page cache control

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Message-ID: <4BA10B66.1020705@redhat.com>
Date:	Wed, 17 Mar 2010 19:03:34 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Christoph Hellwig <hch@....de>
CC:	Chris Webb <chris@...chsys.com>, balbir@...ux.vnet.ibm.com,
	KVM development list <kvm@...r.kernel.org>,
	Rik van Riel <riel@...riel.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kevin Wolf <kwolf@...hat.com>
Subject: Re: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter

On 03/17/2010 06:58 PM, Christoph Hellwig wrote:
> On Wed, Mar 17, 2010 at 06:53:34PM +0200, Avi Kivity wrote:
>    
>> Meanwhile I looked at the code, and it looks bad.  There is an
>> IO_CMD_FDSYNC, but it isn't tagged, so we have to drain the queue before
>> issuing it.  In any case, qemu doesn't use it as far as I could tell,
>> and even if it did, device-matter doesn't implement the needed
>> ->aio_fsync() operation.
>>      
> No one implements it, and all surrounding code is dead wood.  It would
> require us to do asynchronous pagecache operations, which involve
> major surgery of the VM code.  Patches to do this were rejected multiple
> times.
>    

Pity.  What about the O_DIRECT aio case?  It's ridiculous that you can 
submit async write requests but have to wait synchronously for them to 
actually hit the disk if you have a write cache.

-- 
error compiling committee.c: too many arguments to function

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