Re: [Myricom help #6325] --disable-directcopy in mpich

[email protected] said:
> Pete Wyckoff wrote:
> 
> > before that oops.  Are you sure you can call free_pages() on a highmem
> > page?
> 
> > Perhaps I shouldn't be expecting gm to work with linux 2.4.0 with
> > highmem enabled?
> 
> Arghh, now I remember :-)
> We talked with Andrea Archangeli, who manages the Linux VM subsystem, at
> Linux World (thanks to Anas Nashif from Suse). He told us that
> free_page() was not a good idea with higmem pages. The good call is
> __free_pages(). The second call does not need to kmap/kunmap the pages. 
> 
> It's funny, the 2 only places in GM where we have to care about highmem
> pages are in the directcopy code and the free_page() call in the
> deregistration code: exactely where you have problems. The kmap/kunmap
> trick is maybe not safe...

Yeah.

free_page() just looks up the struct page* and calls __free_pages()
anyway.  If all you're trying to do is drop the page count, you can
skip the map/unmap, I think.

Perhaps my issue with the swap was related to the page moving out to
swap during that short time that you have it mapped in.

		-- Pete