Chess engine Updated 2025-07-16
x86 Paging Tutorial Copy-on-write Updated 2025-07-16
Those page faults only happen when a process tries to write to the page, and not read from it.
When Linux forks a process:
- instead of copying all the pages, which is unnecessarily costly, it makes the page tables of the two process point to the same physical address.
- it marks those linear addresses as read-only
- whenever one of the processes tries to write to a page, the makes a copy of the physical memory, and updates the pages of the two process to point to the two different physical addresses
Node.js SQLite bindings Updated 2025-07-16
SQLite isolation levels Updated 2025-07-16
The default isolation level for SQLite is SERIALIZABLE
It does not appear possible to achieve the other two levels besides SERIALIZABLE and READ UNCOMMITED
Deletionism on Wikipedia Updated 2025-07-16
Some examples by Ciro Santilli follow.
Of the tutorial-subjectivity type:
- This edit perfectly summarizes how Ciro feels about Wikipedia (no particular hate towards that user, he was a teacher at the prestigious Pierre and Marie Curie University and actually as a wiki page about him):which removed the only diagram that was actually understandable to non-Mathematicians, which Ciro Santilli had created, and received many upvotes at: math.stackexchange.com/questions/776039/intuition-behind-normal-subgroups/3732426#3732426. The removal does not generate any notifications to you unless you follow the page which would lead to infinite noise, and is extremely difficult to find out how to contact the other person. The removal justification is even somewhat ad hominem: how does he know Ciro Santilli is also not a professional Mathematician? :-) Maybe it is obvious because Ciro explains in a way that is understandable. Also removal makes no effort to contact original author. Of course, this is caused by the fact that there must also have been a bunch of useless edits not done by Ciro, and there is no reputation system to see if you should ignore a person or not immediately, so removal author has no patience anymore. This is what makes it impossible to contribute to Wikipedia: your stuff gets deleted at any time, and you don't know how to appeal it. Ciro is going to regret having written this rant after Daniel replies and shows the diagram is crap. But that would be better than not getting a reply and not learning that the diagram is crap.
rm a cryptic diagram (not understandable by a professional mathematician, without further explanations
- en.wikipedia.org/w/index.php?title=Finite_field&type=revision&diff=1044934168&oldid=1044905041 on finite fields with edit comment "Obviously: X ≡ α". Discussion at en.wikipedia.org/wiki/Talk:Finite_field#Concrete_simple_worked_out_example Some people simply don't know how to explain things to beginners, or don't think Wikipedia is where it should be done. One simply can't waste time fighting off those people, writing good tutorials is hard enough in itself without that fight.
- en.wikipedia.org/w/index.php?title=Discrete_Fourier_transform&diff=1193622235&oldid=1193529573 by user Bob K. removed Ciro Santilli's awesome simple image of the Discrete Fourier transform as seen at en.wikipedia.org/w/index.php?title=Discrete_Fourier_transform&oldid=1176616763:with message:
Hello. I am a retired electrical engineer, living near Washington,DC. Most of my contributions are in the area of DSP, where I have about 40 years of experience in applications on many different processors and architectures.
Thank you so much!!remove non-helpful image
Maybe it is a common thread that these old "experts" keep removing anything that is actually intelligible by beginners? Section "There is value in tutorials written by beginners"Also ranted at: x.com/cirosantilli/status/1808862417566290252
Figure 1. Source at: numpy/fft_plot.py. - when Ciro Santilli created Scott Hassan's page, he originally included mentions of his saucy divorce: en.wikipedia.org/w/index.php?title=Scott_Hassan&oldid=1091706391 These were reverted by Scott's puppets three times, and Ciro and two other editors fought back. Finally, Ciro understood that Hassan's puppets were likely right about the removal because you can't talk about private matters of someone who is low profile:even if it is published in well known and reliable publications like the bloody New York Times. In this case, it is clear that most people wanted to see this information summarized on Wikipedia since others fought back Hassan's puppet. This is therefore a failure of Wikipedia to show what the people actually want to read about.This case is similar to the PsiQuantum one. Something is extremely well known in an important niche, and many people want to read about it. But because the average person does not know about this important subject, and you are limited about what you can write about it or not, thus hurting the people who want to know about it.
Notability constraints, which are are way too strict:There are even a Wikis that were created to remove notability constraints: Wiki without notability requirements.
- even information about important companies can be disputed. E.g. once Ciro Santilli tried to create a page for PsiQuantum, a startup with $650m in funding, and there was a deletion proposal because it did not contain verifiable sources not linked directly to information provided by the company itself: en.wikipedia.org/wiki/Wikipedia:Articles_for_deletion/PsiQuantum Although this argument is correct, it is also true about 90% of everything that is on Wikipedia about any company. Where else can you get any information about a B2B company? Their clients are not going to say anything. Lawsuits and scandals are kind of the only possible source... In that case, the page was deleted with 2 votes against vs 3 votes for deletion.is very similar to Stack Exchange's own Stack Overflow content deletion issues. Ain't Nobody Got Time For That. "Ain't Nobody Got Time for That" actually has a Wiki page: en.wikipedia.org/wiki/Ain%27t_Nobody_Got_Time_for_That. That's notable. Unlike a $600M+ company of course.
should we delete this extremely likely useful/correct content or not according to this extremely complex system of guidelines"
In December 2023 the page was re-created, and seemed to stick: en.wikipedia.org/wiki/Talk:PsiQuantum#Secondary_sources It's just a random going back and forth. Author Ctjk has an interesting background:I am a legal official at a major government antitrust agency. The only plausible connection is we regulate tech firms
For these reasons reason why Ciro basically only contributes images to Wikipedia: because they are either all in or all out, and you can determine which one of them it is. And this allows images to be more attributable, so people can actually see that it was Ciro that created a given amazing image, thus overcoming Wikipedia's lack of reputation system a little bit as well.
Wikipedia is perfect for things like biographies, geography, or history, which have a much more defined and subjective expository order. But when it comes to "tutorials of how to actually do stuff", which is what mathematics and physics are basically about, Wikipedia has a very hard time to go beyond dry definitions which are only useful for people who already half know the stuff. But to learn from zero, newbies need tutorials with intuition and examples.
Bibliography:
- gwern.net/inclusionism from gwern.net:
Iron Law of Bureaucracy: the downwards deletionism spiral discourages contribution and is how Wikipedia will die.
- Quote "Golden wiki vs Deletionism on Wikipedia"
Group axiom Updated 2025-07-16
List of systems programmers Updated 2025-07-16
x86 Paging Tutorial Invalidating TLB entries Updated 2025-07-16
When the process changes,
cr3 change to point to the page table of the new current process.A simple and naive solution would be to completely invalidate the TLB whenever the
cr3 changes.However, this is would not be very efficient, because it often happens that we switch back to process 1 before process 2 has completely used up the entire TLB cache entries.
The solution for this is to use so called "Address Space Identifiers" (ASID) as mentioned in sources such as:
Basically, the OS assigns a different ASID for each process, and then TLB entries are automatically also tagged with that ASID. This way when the process makes an access, the TLB can determine if a hit is actually for the current process, or if it is an old address coincidence with another process.
x86 Paging Tutorial K-ary trees to the rescue Updated 2025-07-16
The algorithmically minded will have noticed that paging requires associative array (like Java
Map of Python dict()) abstract data structure where:The single level paging scheme uses a simple array implementation of the associative array:and in C pseudo-code it looks like this:
- the keys are the array index
- this implementation is very fast in time
- but it is too inefficient in memory
linear_address[0] = physical_address_0
linear_address[1] = physical_address_1
linear_address[2] = physical_address_2
...
linear_address[2^20-1] = physical_address_NBut there another simple associative array implementation that overcomes the memory problem: an (unbalanced) k-ary tree.
Using a K-ary tree instead of an array implementation has the following trade-offs:
In C-pseudo code, a 2-level K-ary tree with and we have the following arrays:
K = 2^10 looks like this:level0[0] = &level1_0[0]
level1_0[0] = physical_address_0_0
level1_0[1] = physical_address_0_1
...
level1_0[2^10-1] = physical_address_0_N
level0[1] = &level1_1[0]
level1_1[0] = physical_address_1_0
level1_1[1] = physical_address_1_1
...
level1_1[2^10-1] = physical_address_1_N
...
level0[N] = &level1_N[0]
level1_N[0] = physical_address_N_0
level1_N[1] = physical_address_N_1
...
level1_N[2^10-1] = physical_address_N_Nand it still contains
2^10 * 2^10 = 2^20 possible keys.K-ary trees can save up a lot of space, because if we only have one key, then we only need the following arrays:
Child of Special Relativity Updated 2025-07-16
norm sequence convergence does not imply pointwise convergence Updated 2025-07-16
Nazi Germany Updated 2025-07-16
x86 Paging Tutorial Kernel vs process memory layout Updated 2025-07-16
The Linux Kernel reserves two zones of virtual memory:
- one for kernel memory
- one for programs
The exact split is configured by
CONFIG_VMSPLIT_.... By default:- on 32-bit:
- on 64-bit: currently only 48-bits are actually used, split into two equally sized disjoint spaces. The Linux kernel just assigns:
- the bottom part to processes
00000000 00000000to008FFFFF FFFFFFFF - the top part to the kernel:
FFFF8000 00000000toFFFFFFFF FFFFFFFF, like this:------------------ FFFFFFFF Kernel ------------------ C0000000 (not addressable) ------------------ BFFFFFFF Process ------------------ 00000000
- the bottom part to processes
Kernel memory is also paged.
In previous versions, the paging was continuous, but with HIGHMEM this changed.
There is no clear physical memory split: stackoverflow.com/questions/30471742/physical-memory-userspace-kernel-split-on-linux-x86-64
x86 Paging Tutorial Memory management unit Updated 2025-07-16
Paging is done by the Memory Management Unit (MMU) part of the CPU.
It was later integrated into the CPU, but the term MMU still used.
Transmon Updated 2025-07-16
Used e.g. in the Sycamore processor.
The most basic type of transmon is in Ciro's ASCII art circuit diagram notation, an LC circuit e.g. as mentioned at youtu.be/cb_f9KpYipk?t=180 from Video "The transmon qubit by Leo Di Carlo (2018)":
+----------+
| Island 1 |
+----------+
| |
X C
| |
+----------+
| Island 2 |
+----------+youtu.be/eZJjQGu85Ps?t=2443 from Video "Superconducting Qubits I Part 1 by Zlatko Minev (2020)" describes a (possibly simplified) physical model of it, as two superconducting metal islands linked up by a Josephson junction marked as The circuit is then analogous to a LC circuit, with the islands being the capacitor. The Josephson junction functions as a non-linear inductor.
X in the diagram as per-Ciro's ASCII art circuit diagram notation:+-------+ +-------+
| | | |
| Q_1() |---X---| Q_2() |
| | | |
+-------+ +-------+Others define it with a SQUID device instead: youtu.be/cb_f9KpYipk?t=328 from Video "The transmon qubit by Leo Di Carlo (2018)". He mentions that this allows tuning the inductive element without creating a new device.
Trillium Notes Updated 2025-07-16
Originally at github.com/zadam/trilium, then after development stopped the community took it up at: github.com/TriliumNext/Notes.
Tree based organization at last. Infinitely deep.
Amazing WYSIWYG, including maths and tables, plus insane plugins like canvas mode, and specific file formats like code/mermaid diagrams/drawing mode.
Intentionally or not, they've basically made an open source Notion, with the possible exception that Notion historically started on web and moved to the desktop, while Trillium went the other way round.
Version history with automatic snapshots at intervals. TODO how is it implemented? Do they just ZIP multiple versions?
No multiuser features. Except for that, could have been a good starting point of an online multiuser thing such as OurBigBook.com!
With Book Notes it is possible possible to see more than one page at a time on the output, which his a major feature of OurBigBook. But does it show on HTML export as well?
You can static HTML export any subtree by right clicking on it in the navigation tree.
HTML export keeps all data as HTML is their native format. This may be inherited from CKEditor. The files are mostly visible, but there is some CSS missing, it is not 100% like editor, notably math is broken. There is also a hosted way of exposing: github.com/zadam/trilium/wiki/Sharing.
trilium.rocks however has a very good export, it is just a question of how much they had to hacked things, source at: github.com/zerebos/trilium.rocks
The default tHTML export uses frame navigation, with a toc fixed on the left frame. Efficient, but not of this century.
There is no concept of user created unique text IDs: you can have the same headers in the same folders in the UI. It's not even a matter of scopes. On exports they are differentiated as
1_name, 2_name, etc../Trilium Demo/Books/To read/1_HR.md
./Trilium Demo/Books/To read/2_HR.md
./Trilium Demo/Books/To read/HR.mdMarkdown export warns:
this preserves most of the formatting
Architecture: runs on local SQLite database via better-sqlite3. Data apparently stored in SQLite database at
~/.local/share/trilium-data, no raw files.Markup is stored as HTML as seen from:
sqlite3 document.db 'SELECT * from note_contents'. HTML is their native storage format, quite interesting. But this means it is not source centric, so any source editing would have to go via import/export. It can be done apparently: github.com/zadam/trilium/wiki/Markdown but involves shoving a ZIP around.WYSIWYG based on ckeditor.com/ which is a dependency. It is kind of cool that the view in which you view the output is exactly the same as the one you edit in, and there is no intermediate format, just the HTML.
Math is KaTeX based.
It also runs on the browser via a server: github.com/zadam/trilium/wiki/Server-installation. And they have a paid service for it at: trilium.cc/. Quite impressive.
They have server to from desktop sync: github.com/zadam/trilium/wiki/synchronization. There is no conflict resolution, one of them wins randomly. But they have revision history, and anything lost will be in the revision history. They have so many features it is mind blowing.
Maintainer announced he would be slowing down development since January 2024: github.com/zadam/trilium/issues/4620?ref=selfh.st
x86 Paging Tutorial PAE and PSE page table schemes Updated 2025-07-16
If either PAE and PSE are active, different paging level schemes are used:
- no PAE and no PSE:
10 | 10 | 12 - no PAE and PSE:
10 | 22.22 is the offset within the 4Mb page, since 22 bits address 4Mb. - PAE and no PSE:
2 | 9 | 9 | 12The design reason why 9 is used twice instead of 10 is that now entries cannot fit anymore into 32 bits, which were all filled up by 20 address bits and 12 meaningful or reserved flag bits.The reason is that 20 bits are not enough anymore to represent the address of page tables: 24 bits are now needed because of the 4 extra wires added to the processor.Therefore, the designers decided to increase entry size to 64 bits, and to make them fit into a single page table it is necessary reduce the number of entries to 2^9 instead of 2^10. - PAE and PSE:
2 | 9 | 21
1965 Nobel Prize in Physics laureate Updated 2025-07-16
How to use an Oxford Nanopore MinION to extract DNA from river water and determine which bacteria live in it Sequencing Updated 2025-07-16
Ciro Santilli's cheapness Updated 2025-07-16
When Ciro was a teenager, he was extremely cheap e.g. for clothes, food and video games even tough his family didn't have bad financial conditions.
This was mostly to save the world by not wasting resources that other people in need could use, and to save money so he could have more money to do more of whatever he wanted without the obligation to work.
But Ciro admits that shocking people with the incredible level of low quality goods was also fun.
Ciro changed after he came to Europe, especially in regards to food, perhaps corrupted by the fact that now the best chocolates, cheeses and breads in the world were not much more expensive than the cheapest brand you could buy. He still hates clothes that are just to look good like costumes though.
Living close to a small favela, São Remo, the favela next to USP, helped Ciro get frighteningly cheap goods on the shop frequented by the favela neighbours.
One legendary story is that of when his flatmate dropped some past on the kitchen floor, and the bowl broke, but Ciro prevented the flatmate from throwing it away and ate some of it nevertheless. What spooked them out the most was Ciro's statement that the pasta now had a crunchy glass shard texture to it.
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