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SubjectRe: Getting FS access events


On Tue, 15 May 2001, Richard Gooch wrote:

> > What happens if you create a buffer cache entry? Does that
> > invalidate the page cache one? Or do you just allow invalidates one
> > way, and not the other? And why=
>
> I just figured on one way invalidates, because that seems cheap and
> easy and has some benefits. Invalidating the other way is costly, so
> don't bother, even if there were some benefits.

Cute.
* create an instance in pagecache
* start reading into buffer cache (doesn't invalidate, right?)
* start writing using pagecache
* lose the page
* try to read it (via pagecache)
Woops - just found a copy in buffer cache, let's pick data from it.
Pity that said data is obsolete...

> So what happens if I dd from the block device and also from a file on
> the mounted FS, where that file overlaps the bnums I dd'ed? Do we get
> two copies in the page cache? One for the block device access, and one
> for the file access?

Yes.

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