Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED_FS

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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."
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