Re: Review of Thomas's >2GB ext2fs proposal

[Neal H. Walfield]

At 17 Aug 2004 02:51:37 -0700,
Thomas Bushnell BSG wrote:
> 
> "Neal H. Walfield" <neal@cs.uml.edu> writes:
> 
> > > Just a small techical correction: we remove mapping only when we are 
> > > remapping page to contain another block.  So when page is evicted, it 
> > > continues to map the same disk block until ext2fs decides that we want 
> > > this page to hold another block (only if page is still evicted, of
> > > course).
> > 
> > Well, I think we ought to drain the mapping cache when the page is
> > evicted.  This keeps memory usage lower.  Further, relative to the
> > cost of reading from disk, adding an entry to the hashes, etc. is
> > cheap.
> 
> I'm confused.  It sounded like Ognyan was saying that the page is
> still assigned to the same area.  But it is necessary to vm_free when
> the kernel tells you to page out.  It is unfriendly (and very bad for
> performance) to hold on to the page.

I never said that I completely agreed with the current
implementation.  There are still parts which I would like to tune.  In
fact, it my message from the 2nd titled "Ognyan's libpager changes" I
explain that

    I have begun to review your ext2fs patch for large file system
    support.  At this point, I have only reviewed the libpager changes
    in any detail.

Although I have since studied his changes to ext2fs, I have not yet
posted my reaction on this list.

Neal