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Date: Wed, 15 Feb 2012 15:57:47 -0800
From: Arun Sharma <asharma@fb.com>
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Subject: Re: [PATCH v5 3/3] fadvise: implement POSIX_FADV_NOREUSE
References: <1329006098-5454-1-git-send-email-andrea@betterlinux.com> <1329006098-5454-4-git-send-email-andrea@betterlinux.com> <20120215233537.GA20724@dev3310.snc6.facebook.com> <20120215234724.GA21685@thinkpad>
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To: Andrea Righi <andrea@betterlinux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Minchan Kim <minchan.kim@gmail.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Johannes Weiner <jweiner@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Shaohua Li <shaohua.li@intel.com>, =?windows-1252?Q?P=E1draig_Brady?= <P@draigBrady.com>, John Stultz <john.stultz@linaro.org>, Jerry James <jamesjer@betterlinux.com>, Julius Plenz <julius@plenz.com>, linux-mm <linux-mm@kvack.org>, linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>



On 2/15/12 3:47 PM, Andrea Righi wrote:
>> index 74b6a97..b4e45e6 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -9,7 +9,6 @@
>>   #include<linux/limits.h>
>>   #include<linux/ioctl.h>
>>   #include<linux/blk_types.h>
>> -#include<linux/kinterval.h>
>>   #include<linux/types.h>
>>
>>   /*
>> @@ -656,7 +655,7 @@ struct address_space {
>>   	spinlock_t		private_lock;	/* for use by the address_space */
>>   	struct list_head	private_list;	/* ditto */
>>   	struct address_space	*assoc_mapping;	/* ditto */
>> -	struct rb_root		nocache_tree;	/* noreuse cache range tree */
>> +	void			*nocache_tree;	/* noreuse cache range tree */
>>   	rwlock_t		nocache_lock;	/* protect the nocache_tree */
>>   } __attribute__((aligned(sizeof(long))));
>>   	/*
>
> mmh.. a forward declaration of rb_root in fs.h shouldn't be better than
> this?
>

Forward declaration works if the type was struct rb_root *. But the type 
in your patch was a struct and the compiler can't figure out its size.

include/linux/fs.h:659:17: error: field ?nocache_tree? has incomplete type

Did you mean forward declaring struct rb_node instead of rb_root?

If we go down this path, a few more places need fixups (I ignored the 
compiler warnings about casting void * to struct rb_root *).

  -Arun

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