> I went hunting for the widely reported oops in 2.1.87 and found the following.
> The problem is the PROT_NONE changes, or rather the changes to the SWP_TYPE
> and SWP_ENTRY macros.
> SHM_SWP_TYPE is defined to be 0x40, so left shifting by two and then masking
> to the bottom 8 bits loses badly :-(
[snipped]
> Since we now need 2 bits for the PAGE_PRESENT, I suspect changing the value of
> SHM_SWP_TYPE in include/linux/swap.h to 0x20 should work (since MAX_SWAPFILES
> is 8, and this seems to be the other use for the type part, I don't see a
> clash). Alternatively, since the shared memory id and offset are currently
> encoded in 22 bits for a shared memory page, the split could be changed to
> 23:9 from 24:8, but I don't know all the repurcussions.
Beware of doing this, I remember that some people with large systems
changed MAX_SWAPFILES from 8 to 16 because the current limit on swap space
with 4kB pages (1Gb total, 128 Mb per file) is simply too small by today's
standards, and the one I would like to see removed for 2.2 if possible.
Gabriel.
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