Rik van Riel wrote:
>
> On Sat, 3 Jun 2000, Matt Yourst wrote:
>
> > Here's my partially-working patch that adds "virtual mapping"
> > support to ramfs. This is a *very* early version of it, since it
>
> It's also pretty complex.
>
That's exactly what I was thinking in some cases too (the comments in the code indicate this.) For instance, in virtual_map_readpage, I didn't know how to solve the problem of removing the hashed swap entry only *after* the page is physically in RAM. Right now it's read synchronously, but that's obviously bad performance-wise. An async swap page read would need to update the hash table and swap map as part of the I/O completion/unlocking itself, which would probably mean extra work elsewhere.
>
> Maybe it would be easier if try_to_swap_out would just
> unmap the page and set a special flag in the page, and
> then shrink_mmap() could push the page to disk.
>
I'll take a look at this and see if I can make my code more robust. It worked fairly well when I first tried it back in 2.3.33, but it broke easily with newer kernels and all the recent VM system changes (I was lucky I could get the patch I sent you working at all!)
>
> (proper write clustering for that will be implemented
> in 2.5, possibly by me)
>
That's another issue that I didn't know how to handle - even though page writes are clustered by the mmap code, they may be scattered anywhere in the swap file with my approach (again, not good for performance unless higher-level code specially handles this case.)
- Matt Yourst
-------------------------------------------------------------
Matt T. Yourst Massachusetts Institute of Technology
yourst@mit.edu 617.225.7690
513 French House - 476 Memorial Drive - Cambridge, MA 02136
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