Lorenzo Stoakes
Posts
5724Following
218Followers
554C/C++/(rust at some point!)
Book - https://linuxmemory.org/
Me - https://ljs.io/
Music - https://soundcloud.com/distal_music/
Arsenal fan, cat maniac, synth experimentalist. Brit.
Opinions are all my own and represent nobody else.
Lorenzo Stoakes
ljs
Was hoping I could finish the swap chapter today, but swap readahead has thwarted me.
Back on it tmr.
Back on it tmr.
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alice
lexd0g@wetdry.worldi cant login to discord because they forgot to add the 0 key to the numpad
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Lorenzo Stoakes
ljs
Signs the book is (too?) big - I am constantly having to grep for things to see if I mentioned them before...
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Lorenzo Stoakes
ljs
One of the ways you can get tripped up in kernel code is that sometimes something really major happens and it isn't in any way highlighted.
For instance - when reading from disk into a folio (whether file-backed or from swap), the folio is locked and will become unlocked once it is 'uptodate' (i.e. has the PG_uptodate flag set).
That renders all instances of trying to lock a folio a barrier that either waits for the read to happen or, as if often the case, incorporates some ability to tell the caller 'ok I need to wait on I/O try again later' as userland experiences with async I/O.
A good example of this is do_swap_page() [0], where we kick off either a synchronous or async read from disk (see block starting at line 3766), but later (line 3878) indicate SIGBUS if the page isn't uptodate.
The key here? Line 3826:
locked = lock_page_or_retry(page, vma->vm_mm, vmf->flags);
We try to lock the page, if I/O is done already we can, if it was synchronous we can, otherwise we either return VM_FAULT_RETRY to indicate the I/O is needed or we wait to acquire the lock.
After this line, we can safely assume the swap has been read from.
I kind of feel that a comment would be helpful here :>) [checking tip I see there isn't one, might add one myself], at the same time it's sort of assumed you'd know this was the case...
While I'm writing the book primarily to learn the mm in more depth, I hope pointing out stuff like this in it will help others over these kind of stumbling blocks.
[0]: https://elixir.bootlin.com/linux/v6.0/source/mm/memory.c#L3718
For instance - when reading from disk into a folio (whether file-backed or from swap), the folio is locked and will become unlocked once it is 'uptodate' (i.e. has the PG_uptodate flag set).
That renders all instances of trying to lock a folio a barrier that either waits for the read to happen or, as if often the case, incorporates some ability to tell the caller 'ok I need to wait on I/O try again later' as userland experiences with async I/O.
A good example of this is do_swap_page() [0], where we kick off either a synchronous or async read from disk (see block starting at line 3766), but later (line 3878) indicate SIGBUS if the page isn't uptodate.
The key here? Line 3826:
locked = lock_page_or_retry(page, vma->vm_mm, vmf->flags);
We try to lock the page, if I/O is done already we can, if it was synchronous we can, otherwise we either return VM_FAULT_RETRY to indicate the I/O is needed or we wait to acquire the lock.
After this line, we can safely assume the swap has been read from.
I kind of feel that a comment would be helpful here :>) [checking tip I see there isn't one, might add one myself], at the same time it's sort of assumed you'd know this was the case...
While I'm writing the book primarily to learn the mm in more depth, I hope pointing out stuff like this in it will help others over these kind of stumbling blocks.
[0]: https://elixir.bootlin.com/linux/v6.0/source/mm/memory.c#L3718
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@dougmerritt @cwayne @sven haha I was kidding about arby's, seems a meme for bad restaurants (might be wrong though).
To be honest with diet the odds of me really eating much of interest are very low, and I'm an addict to food man, I can't let myself off really.
Except maybe MAYBE for an in'n'out. One, no fries... maybe more steps? :)
To be honest with diet the odds of me really eating much of interest are very low, and I'm an addict to food man, I can't let myself off really.
Except maybe MAYBE for an in'n'out. One, no fries... maybe more steps? :)
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Lorenzo Stoakes
ljs
@marzee @fromjason yes me too! Sits in the corner quietly and prints when told to. Glorious (low bar in the printer world!)
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ljs
A great deal of harm has been done to society by people who have zero understanding of the internet and social media taking things said there at face value.
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ljs
@djasa @overholt LOL well Altman is utter and complete scum and I'm sure if you dug deep you'd find... issues with him.
Silicon valley attracts these 'types' rather well, sadly.
His lying about LLMs has been a huge part of kicking off this hideous wave of bullshit we're in now.
And then there's the stuff about his sister, rumours I heard, that I won't repeat because the UK has dreadful defamation laws. But you can google ;)
Silicon valley attracts these 'types' rather well, sadly.
His lying about LLMs has been a huge part of kicking off this hideous wave of bullshit we're in now.
And then there's the stuff about his sister, rumours I heard, that I won't repeat because the UK has dreadful defamation laws. But you can google ;)
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John Overholt
overholt@glammr.usAm I so out of touch? No, it’s the ethics that are wrong. https://news.harvard.edu/gazette/story/2024/05/did-student-or-chatgpt-write-that-paper-does-it-matter/?utm_source=SilverpopMailing&utm_medium=email&utm_campaign=Daily%20Gazette%2020240503%20(1)
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@pinkforest @calbaker @laund Not pointing fingers to any particular community, project or even language but here's something I observe in modern days of open source.
There has been and probably is still today some toxic behavior for sure in open source projects but there is also some toxic positivity, which means that when you take more critical angle it is interpreted as toxic behavior.
There has been and probably is still today some toxic behavior for sure in open source projects but there is also some toxic positivity, which means that when you take more critical angle it is interpreted as toxic behavior.
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