Re: 2.5.68-mm2

Andrew Morton (akpm@digeo.com)
Wed, 23 Apr 2003 14:46:48 -0700


"Martin J. Bligh" <mbligh@aracnet.com> wrote:
>
> > . I got tired of the objrmap code going BUG under stress, so it is now in
> > disgrace in the experimental/ directory.
>
> Any chance of some more info on that? BUG at what point in the code,
> and with what test to reproduce?

A bash-shared-mapping (from ext3 CVS) will quickly knock it over. It gets
its PageAnon/page->mapping state tangled up.

Must confess that I have trouble getting excited over objrmap. It introduces

- inconsistency (pte_chains versus vma-list scanning)

- code complexity

- a quadratic search

- nasty, nasty problems with remap_file_pages(). I'd rather not have to
nobble remap_file_pages() functionality for this reason.

and what do we gain from it all? The small fork/exec boost isn't very
significant. What we gain is more lowmem space on
going-away-real-soon-now-we-sincerely-hope highmem boxes.

Ingo-rmap seems a better solution to me. It would be a fairly large change
though - we'd have to hold the four atomic kmaps across an entire pte page
in copy_page_range(), for example. But it will then have good locality of
reference between adjacent pages and may well be quicker than pte_chains.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/