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x86 Paging Tutorial Single level paging scheme visualization Updated 2025-07-16
This is how the memory could look like in a single level paging scheme:
Links Data Physical address
+-----------------------+ 2^32 - 1
| |
. .
| |
+-----------------------+ page0 + 4k
| data of page 0 |
+---->+-----------------------+ page0
| | |
| . .
| | |
| +-----------------------+ pageN + 4k
| | data of page N |
| +->+-----------------------+ pageN
| | | |
| | . .
| | | |
| | +-----------------------+ CR3 + 2^20 * 4
| +--| entry[2^20-1] = pageN |
| +-----------------------+ CR3 + 2^20 - 1 * 4
| | |
| . many entires .
| | |
| +-----------------------+ CR3 + 2 * 4
| +--| entry[1] = page1 |
| | +-----------------------+ CR3 + 1 * 4
+-----| entry[0] = page0 |
| +-----------------------+ <--- CR3
| | |
| . .
| | |
| +-----------------------+ page1 + 4k
| | data of page 1 |
+->+-----------------------+ page1
| |
. .
| |
+-----------------------+ 0Notice that:
- the CR3 register points to the first entry of the page table
- the page table is just a large array with 2^20 page table entries
- each entry is 4 bytes big, so the array takes up 4 MiB
- each page table contains the physical address a page
- each page is a 4 KiB aligned 4 KiB chunk of memory that user processes may use
- we have 2^20 table entries. Since each page is 4 KiB == 2^12, this covers the whole 4 GiB (2^32) of 32-bit memory
x86 Paging Tutorial Why not a balanced tree Updated 2025-07-16
Learned readers will ask themselves: so why use an unbalanced tree instead of balanced one, which offers better asymptotic times en.wikipedia.org/wiki/Self-balancing_binary_search_tree?
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Mailing list Updated 2025-07-16
The only explanation is that the dinosaurs who created the projects are unable to adapt to new superior technologies.
Yes, Ciro is talking to you, big fundamental projects from last century: Linux kernel, GNU Compiler Collection (gcc.gnu.org/lists.html), Binutils (sourceware.org/binutils/), etc.
Some of you are already using Bugzilla for the bugs, so kudos. But if you've seen their benefit, why you still use the mailing list for patches?
Advantages of mailing lists:
- threaded replies, which almost no issue tracker has. GitHub feature request: github.com/isaacs/github/issues/837
Disadvantages: everything else:
- cannot subscribed to a single thread. Which forces you to create an email filter for each one of them you subscribe to.
- no metadata, notably the notion of closing / merging, but also upvotesYou have to read thirty messages before you can know if the bug was solved or not.
- it is insanely hard to reply to messages from before you were subscribed: webapps.stackexchange.com/questions/23197/reply-to-mailman-archived-message/115088#115088
- hard to apply patches locally to test them out: stackoverflow.com/questions/5062389/how-to-use-git-am-to-apply-patches-from-email-messages/49082916#49082916Unless they use Patchwork, which adds one more website on top of the mess.And then Gmail corrupts your patches, and you are forced to use
git send-email, which does not work on some network configurations: stackoverflow.com/questions/28038662/how-to-solve-unable-to-initialize-smtp-properly-when-using-using-git-send-ema or setup ThunderBird. - often have to subscribe to post at all, thus cluttering your inbox further
- you can edit posts to make them clearer.Yes, people could vandalize their answers when they get mad, and threads might stop making sense after edits. But this can be solved with an undeletable post history like Stack Overflow has (but not any other tracker does).Or archive.org :-)In any case, what do you think will happen more often and have greater impact:
- people vandalize their posts
- people fix their silly typos and improve content
- searchable by author, keyword, etc. without Google. Yes, mailing list trackers could have decent implementations to overcome that. But no, GNU Mailman which everyone uses does not have it. Google barely indexes it.
- people have to learn about top posting vs inline posting, and this requires infinite education of new users
- On mailing lists: either put a comment in the middle of a huge patch and let other people find it, or (more likely) copy paste the part of the patch that you are talking about.
- most mail web UIs suck.OK, this is not an unsolvable or intrinsic problem, but still a problem.E.g.:
ezmlmit is not possible to see the entire content in a single page: gcc.gnu.org/ml/gcc/2015-07/threads.html.The alternative: do like LLVM and send attachments. Yes, I we all love opening up attachments on our browsers.The real solution: everyone can create branches and pull requests. Also has the benefit of running CI on the pull requests.
Not sure:
- you can have infinitely many trackers to replicate data in case apocalypse happens in some part of the world.Although I'm not sure this is an advantage, as you don't know anymore which one is the canonical trackers an advantage, as you don't know anymore which one is the canonical tracker.And all web interfaces already have an API to export messages, and someone has already scripted it to import from any web UI to any web UI for you.
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Git tips Linear history vs branching Updated 2025-07-16
Some people like merges, but they are ugly and stupid. Rebase instead and keep linear history.
Linear history:
5 master
|
4
|
3
|
2
|
1 first commitBranched history:
7 master
|\
| \
6 \
|\ \
| | |
3 4 5
| | |
| / /
|/ /
2 /
| /
1/ first commitWhich type of tree do you think will be easier to understand and maintain?
????
????????????
You may disconnect now if you still like branched history.
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The reason why the epsilon delta definition is so venerated is that it fits directly into well known methods of the formalization of mathematics, making the notion completely precise.
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