Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED_FS

[Matthew Wilcox <matthew@wil.cx>]

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.

(hm, what about block devices not currently mounted?  do we need to check
whether mapping->host is NULL?)

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."