in a *very* recent posting (thanks Sun-Managers!), I was having
trouble mmap(2)'ing a very large region (1-2Gbytes)
I thought it was related to the datasize limit. So I tried to
increase the size of the data segment, without success
Dave Probert (probert@cs.ucsb.edu) give me very usefull information
(See his posting at the end of this letter) :
"There is a hole in the MMU between virtual addresse 0x20000000 - 0xdfffffff"
This is right only for 4/20..4/75 ; With my 4/470, the datasize
limit is 2 Gb.
1) the datasize limit in a Sparc 1 or Sparc 2 can't be increased over
0x20000000 (524288 KB). It's a hard limit. Modifying /sys/sun4c/vmparam.h
doesn't change anything.
2) You can't mmap more than this value. Moreover, the sum of the mmaps
in your program can't exceed 524288 KB
3) on a 4/470 (where the datasize limit is 2Gb and where there is no
hole in the MMU), you can mmap more than 2Gb ; The limit seems
to be around 3.5 Gb ; Be careful, you can't map more than 2 Gb
in one mmap syscall. So, to map 3.5 Gb, you have to do at least
2 syscalls (I think it's a bug in mmap : If len > 2 Gb, then
it becomes < 0... and ernno is set to EINVAL ; There are same
things in write(2)). I think it's better not to go beyond the 2Gb limit...
The following test completes (on the 4/470):
open
truncate 2Gb
mmap 2Gb
write 1 byte each 20 Mb
munmap - close
The created file was 2Gb, with 2000 blocks allocated
(as reported by ls -ls) : Succeeded.
Some people speculate on the missuse of csh'limit ; Sorry, it was
not that !
Special thanks to Dave Probert <probert@cs.ucsb.edu>
and to
mattson@cs.UCSD.EDU
Hans van Staveren <sater@cs.vu.nl>
------------------------------------------------------------------------------
Claude Scarpelli Internet : claude@genethon.fr
Human Polymorphism Study Center or : claude@cephb.fr
Included message :
----------------
----- Begin Included Message -----
>From probert%cs@hub.ucsb.edu Mon Oct 14 20:25:58 1991
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Date: Mon, 14 Oct 91 12:25:15 PDT
From: Probert <probert%cs@hub.ucsb.edu>
Posted-Date: Mon, 14 Oct 91 12:25:15 PDT
To: claude@genethon
In-Reply-To: Claude Scarpelli's message of Mon, 14 Oct 91 16:22:15 +0100 <9110141522.AA24258@genethon.genethon.fr>
Subject: large mmap(2)
Reply-To: probert%cs@hub.ucsb.edu
Status: R
Perhaps this information will help. In the Sparc MMU architecture (the
current one, not the new reference one which first appears in Galaxy),
there is a hole in the mmu between virtual addresses
0x20000000 - 0xdfffffff
[(echo hole_start/X; echo hole_end/X) | adb /vmunix /dev/kmem]
0x20000000 = 524288 KB.
So this is a hard limit in the hardware for the size of the data segment.
-- Dave Probert probert@cs.ucsb.edu----- End Included Message -----
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