linux-kernel - Re: [PATCH] aio: propogate post-EIOCBQUEUED errors to completion event

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Message-Id: <528148DD-0533-4D82-A242-25A4C5D1A977@oracle.com>
Date:	Tue, 20 Feb 2007 10:40:03 -0800
From:	Zach Brown <zach.brown@...cle.com>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Benjamin LaHaise <bcrl@...ck.org>,
	"Ananiev, Leonid I" <leonid.i.ananiev@...el.com>,
	linux-aio@...ck.org, linux-kernel@...r.kernel.org,
	Suparna bhattacharya <suparna@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] aio: propogate post-EIOCBQUEUED errors to completion event

>> There are some strange O_DIRECT corner cases in here such that the  
>> 'last
>> writer' may actually be a 'last reader' and winning can mean have  
>> a copy
>> of the page in page cache older than the copy on disk.
>
> As long as it is marked dirty so that it eventually gets synced to  
> disk,
> it shouldn't matter.

No, Chris is pointing out that an an O_DIRECT write can leave clean  
read pages in the page cache.

All it takes is giving a source buffer for the write which is an mmap 
()ed apeture of the region that is being written to.  If you get the  
offsets right you can get the get_user_pages() down in fs/direct-io.c  
will populate the page cache before the actual O_DIRECT write gets to  
it.

- z
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