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diff --git a/open_issues/placement_of_virtual_memory_regions.mdwn b/open_issues/placement_of_virtual_memory_regions.mdwn new file mode 100644 index 00000000..95b9e545 --- /dev/null +++ b/open_issues/placement_of_virtual_memory_regions.mdwn @@ -0,0 +1,89 @@ +[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_gnumach]] + +IRC, freenode, #hurd, 2011-07-13 + + <braunr> does anyone know if posix (or mach) has requirements or a policy + about the placement of allocations of virtual space ? + <braunr> a policy such as bottom-up ? + <braunr> or "find lowest vailable space" ? + <jkoenig> braunr, you mean for vm_allocate ? You may want to check mmap() + but I can't remember ever coming across such a thing (except maybe + wrt. alignment) + <braunr> i was wondering how e.g. libraries are linked near the stack + (possibly at slightly random addresses) + <braunr> does the linker walk the address space entries top-down ? + <braunr> jkoenig: i didn't see anything either in the mach interface, but i + may have missed something + <braunr> jkoenig: most systems i've been studying mark the vm regions for + the heap and the stack + <braunr> but for mach, the stack is just allocated virtual memory at the + top of the space + <braunr> so the "placement policy" is either completely outside the kernel, + or relies on its interface + <jkoenig> braunr, actually I'm surprised Mach would even dictate where the + (one?) stack should be, I would have expected it to be the job of + whatever creates a thread to make this kind of choice + <braunr> jkoenig: threads have their own stacks, under the responsibility + of the user trhead implementation + <braunr> but a program usually needs a stack even before it runs + <braunr> i had to set one to bootstrap modules in v0.1 + <braunr> but i wonder if it's just for bootstrapping (and then propagated + by fork()) or part of the interface + <braunr> but this doesn't matter much actually, the allocation mechanism i + have in mind can actually support multiple policies + <jkoenig> I would guess the former (just for bootstrapping), since a new + task has no thread, and a new thread has no state. (but I'm no expert) + <braunr> i think so + <braunr> i'll have a look at the exec server + <braunr> jkoenig: did the previous implementation of procfs show task maps + ? + <jkoenig> braunr, I don't think so, I would probably have felt compelled to + include them in the new one if it did :-) + <braunr> hmmm + <braunr> we definitely need that + <jkoenig> is there a compelling use case you think about in particular? + <braunr> yes + <braunr> i failed to understand how gnumach behaved wrt ipc right spaces + +[[rework_gnumach_ipc_spaces]] + + <braunr> and when i did, i found out my work was impossible to integrate + <jkoenig> "ipc right spaces" ? + <braunr> each task have an ipc space, which contains righs + <braunr> rights + <braunr> the ipc translation layer converts space/name and space/port + tuples to rights + <braunr> i wanted to replace the splay tree with a radix tree but didn't + get how the ipc table made the splay tree almost unused + <braunr> i don't want to make this kind of mistake again, so i'd like a + clear and detailed view of the vm spaces + <braunr> (it's only compelling for myself, all right) + <braunr> but + <braunr> we have vminfo + <braunr> rbraun@nordrassil:~$ vminfo $$ | wc -l + <braunr> 1046 + <braunr> oh my + <braunr> in comparison, a firefox instance has less than 500 on linux + <jkoenig> you mean there's some kind of port name table (or functional + equivalent) which actually resides in the task's memory? (and that's what + shows up at the beginning of the address space with prot=0?) + <braunr> jkoenig: sorry for being confusing, it's not that at all + <jkoenig> (btw feel free to tell me to just go read the source or whatever) + <braunr> jkoenig: don't worry + <jkoenig> braunr, no problem + <braunr> jkoenig: i just compared a previous attempt to improve gnumach + which failed because i didn't have enough insight of the inner workings + of the kernel + <braunr> jkoenig: i really want to miss as little as possible on the vm + part, so having detailed information about what actually happens on + running hurd systems is something i need |