linux-kernel - Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED

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Date:	Wed, 27 Apr 2011 14:49:25 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Andrea Righi <andrea@...terlinux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, linux-fsdevel@...r.kernel.org,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED_FS

On Wed, Apr 27, 2011 at 14:47, Matthew Wilcox wrote:
> On Wed, Apr 27, 2011 at 02:39:53PM -0400, Mike Frysinger wrote:
>> > Mmm ... what if I open /dev/sdxyz and call fadvise() on it? ??I think
>> > you end up flushing /dev's page cache entries, instead of the filesystem
>> > which is on /dev/sdxyz.
>>
>> i was thinking of that, but was trying to come up with situations
>> where there might not have a node to work on.  fs's in a file go
>> through loop devs, dm/lvm have ones created, and flash fs's still have
>> a mtd block.  how about network based fs's ?  how you going to signal
>> dropping of pages for nfs or cifs or fuse ones ?
>
> For a regular file, mapping->host->i_sb points to the superblock this
> file is on.  For a device, mapping->host->i_sb points to the superblock
> corresponding to this device.  So it's always what we want.

sorry, wrong question.  i misread your original post (suggesting we
should be calling fadvise on the block instead of an arbitrary dir
handle).
-mike
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