Yesterday s
RAM mystery was
solved after dozens of people have written in with helpful
comments. Thank you all. I
need to find time to create a
proper, commentable blog soon so that you all can get the credit
you deserve!
I now have the full 4GB of RAM available:
$ free head -2
total used free shared buffers cached
Mem: 4063324 1657440 2405884 0 149080 643732
Yay!
The suggestions ranged from timing issues to defective modules,
from 64bit OS via south/north bridge limitations to sacrificing
chickens to god spongebobs.
In the end, several people put their finger on a concept called
memory hole remapping , and that turned out to be the ticket. Here
is what I learnt:
This motherboard and the CPU memory controller supports (which
means can address ) 4096MB of RAM. Since extensions cards, such as
the graphics card and the network controller, also need addressable
slabs of memory for their RAM or registers, ranges in the upper
memory regions are mapped to the RAM of those cards.
The file
/proc/mtrr gives a clue over what s
happening:
reg00: base=0x000000000 ( 0MB), size= 2048MB, count=1: write-back
reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
reg02: base=0x0c0000000 ( 3072MB), size= 256MB, count=2: write-combining
reg03: base=0x0d8000000 ( 3456MB), size= 128MB, count=1: write-combining
reg04: base=0x0e8000000 ( 3712MB), size= 64MB, count=1: write-combining
reg05: base=0x0ec000000 ( 3776MB), size= 64MB, count=1: write-combining
Registers 0 and 1 represent the addressable RAM available to the
operating system. At position 3072, we find two slabs of 256MB
each, most likely corresponding to the two graphics cards in the
system. I
think that the 128MB in register 3 is the AGP
aperture. Registers 4 and 5 correspond to 64MB slabs each, most
likely relating to the two network cards I have installed.
The result is that addresses in memory beyond 3072MB are
routed to the extension cards, which overshadow the original
system RAM and leave it unusable.
When I turned on the memory hole remapping feature in the
BIOS, I empowered the BIOS to remap the memory space. The way it
does this is BIOS-dependent, but most likely, it will remap the
overshadowed memory region to the end of the total memory space.
This is a software-only remapping, but the effect is that the
system appears to have more memory.
/proc/mtrr now reads:
reg00: base=0x000000000 ( 0MB), size= 4096MB, count=1: write-back
reg01: base=0x100000000 ( 4096MB), size= 1024MB, count=1: write-back
reg02: base=0x0c0000000 ( 3072MB), size= 1024MB, count=1: uncachable
reg03: base=0x0c0000000 ( 3072MB), size= 256MB, count=1: write-combining
I am not entirely sure how to interpret this yet, but you can
see that there are now an additional 1024MB at position 4096
(register 1), so the system seems to have 5GB of RAM available.
Register 2 describes memory between 3072 and 4096 as not cacheable,
because it maps to extension cards. I do not know how register 3
fits into the picture.
By remapping, we cross the 4096MB mark. To make use of the
additional memory, we will need
PAE
enabled to give you 36 bits, or a 64bit operating system: 2^32
is 4096M, so with only 32 bits available, 4GB is all the memory
that can ever be addressed (dirty hacks excluded). Fortunately,
this system has been running the
Debian amd64 port even
before it was officially released, and thus, once the BIOS remapped
the memory, I could fully make use of it.
Mystery solved, some knowledge acquired, many of you left to
thank!
Many moons ago while doing fieldwork I went to a radical tech activist camp sponsored by The Ruckus Society to give a presentation on Free Software (which I actually still have online in the gaudy orange I so loved. I could only stay 2 days as I had to go to Debconf2 in Toronto for fieldwork but it forever changed my life in pretty significant ways.
One remarkable thing about Ruckus was that for the first time I meet a particular kind of geek I had yet to come across: the crunchy and chewy granola/environmentalist/hippie hacker a type of hacker that can be found world over but is likely to be (unsurprisingly) living, sometimes in the trees (literally) in the Pacific Northwest. They are one of my favorite kind of people as I can talk endlessly to them about 2 of my great passions: Free Software and environmental justice. Comfrey, pictured above, was one such hacker from Portland who I met at the Ruckus event and now routinely shows up, usually unannounced to our house at least 1-2x a year.
I woke up this morning to find him on our couch, got a bunch of knot-weed to chew on compliments of his foraging, and took the afternoon off to share some food. Among many stories, he told me of a new transportational pursuit of his, Roller-Hitching, which he uses to get around the country. He uses old school roller skates to skate along the road, even highways, until he gets picked up and get where he needs to go.
Naturally, these old school states are not just functional in the sense that they are faster than two feet in motion, but since they signify a particular spirit of the 1970s you know, the groovy, dynamite, free love spirit of things, they draw positive attention and apparently when he roller-hitches, he gets picked up frequently (and made it from Minneapolis to Portland in 2 hours and 2 days: not shabby).
In California while on the 101 north of Arcata, California, Comfrey got stopped by the highway patrol and basically the cop wanted to kick him off on the grounds the he was a pedestrian (apparently prohibited on this patch of the 101). Comfrey, being a bright fellow, basically noted that roller skating is not really a pedestrian activity, that he was using, much a like a biker, a transportation device of sorts, so that he was in a grey zone between bikes and walking.
At the time, the cop was convinced enough but did tell Comfrey to look up the law in the library cuz the next time he would give him a ticket and the next time after that throw him in jail. Comfrey has yet sourced the law but soon will. When he does, since I like to report on geeks and the law, I too will report on whether one can roller skate down or up the highway for those that might want to give Roller-Hitching a try.
Serve creates goroutines via the go
keyword; each of which tries to get a slot in the channel. In the
example there are only 3 slots, so it acts like a semaphore of count
3. When done, each thread returns its slot to the channel, which
allows anyone blocked to be woken and continued.
This instantly reminded me of the very first thing you need to do
if you ever want to pass 
Look familiar? Instead of a blocking push of a number into a slot
into a channel, you make a blocking IPC call to a remote server.
My point here is that both take the approach of sharing memory via
communication. When using IPC, you bundle up all your information
into the available slots in the IPC message and send it. When using a
channel, you bundle your information into an entry in the channel and
call your goroutine. Receiving the IPC is the same as draining a
channel - both result in you getting the information that was bundled
into it by the caller.
While examining the mail queue after a big mail server migration, I
found the following reason for a bounce (hostnames replaced according
to 
I knew that / (slash) activated the Quick Find in Firefox and its close relations, but I didn t know that ' (apostrophe) activated a Quick Find (in links). That s quite helpful when jumping through web admin interfaces where I know which links I want, I m using the two-handed keyboard (not 
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I've spent chunks of the last couple of days fighting a problem that's existed for about 25 years. The 8086 was a 16-bit processor with a 20-bit address space, limiting the maximum physical address that could be accessed to 1MB. However, quirks of the segmented memory system meant that addresses greater than 1MB could be constructed - these would wrap around to the bottom of memory. Because loading the segment registers was a time consuming operation, some programmers used this behaviour as a performance optimisation.
Ever since my 
Almost exactly a year ago, the term "Custom Debian Distribution" was changed to [1 "Debian Pure Blends"] to better reflect what it is about: a variation of Debian within Debian. So far, so good. Then there are also "Debian Blends", which are not pure, meaning they have some parts which are not yet in Debian.