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diff --git a/user/Maksym_Planeta.mdwn b/user/Maksym_Planeta.mdwn new file mode 100644 index 00000000..c44a4fcb --- /dev/null +++ b/user/Maksym_Planeta.mdwn @@ -0,0 +1,135 @@ +[[!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]]."]]"""]] + +[[!toc]] +#Notes on tmpfs + +## mach-defpager + +[[defpager|http://www.bddebian.com:8888/~hurd-web/user/Maksym_Planeta/#defpager81111]] + +[[http://www.mail-archive.com/bug-hurd@gnu.org/msg18859.html]] + +## Steps + +1. Find out what causes crashes in tmpfs with defpager + +[[http://www.gnu.org/s/hurd/hurd/translator/tmpfs/notes_various.html]] + +TODO: Consider deleting of parameter "port" in function mach-defpager/default_pager.c:pager_port_list_insert +since this parameter is unused + +2. Write own pager + + 6.11.11 Reading/writing for files that fit in vm_page_size works + + 7.11.11 Works for any size. + +3. Make links work + + Symlinks behavior: [[links|http://www.bddebian.com:8888/~hurd-web/user/Maksym_Planeta/#links81111]] + + 8.11.11 Symlinks work. + +4. Control of used space by tmpfs. + + TODO: Make tmpfs use not more space than it was allowed. + +5. Thread safety. + + TODO: During execution tmpfs hangs in random places. The most possible is variant is deadlocks, + because nothing was undertaken for thread safety. + +6. After sometime of inactivity tmpfs exits. + + TODO: Find out why and correct this. + +#Debugging + +To debug tmpfs, using libraries from "$PWD"/lib and trace rpc: + + settrans -ca foo /usr/bin/env LD_LIBRARY_PATH="$PWD"/lib utils/rpctrace -I /usr/share/msgids/ tmpfs/tmpfs 1M + LD_LIBRARY_PATH="$PWD"/lib gdb tmpfs/tmpfs `pidof tmpfs` + +For debugging ext2fs: + + settrans --create --active ramdisk0 /hurd/storeio -T copy zero:32M && \ + /sbin/mkfs.ext2 -F -b 4096 ramdisk0 && \ + settrans --active --orphan ramdisk0 /usr/bin/env LD_LIBRARY_PATH="$PWD"/lib utils/rpctrace -I /usr/share/msgids/ \ + ext2fs/ext2fs.static ramdisk0 + +#Questions + +1. What are sequence numbers? What are they used for? +2. Is there any way to debug mach-defpager? When I set breakpoint to any function in it, pager never breaks. + +#Conversations + +## 8.11.11 + +### links<a id="links81111"/> + (10:29:11) braunr: mcsim: ln -s foo/bar foo/baz means the link name is baz in the foo directory, + and its target (relative to its directory) is foo/bar (which would mean /tmp/foo/foo/bar in canonical form) + (10:29:42) braunr: youpi: tschwinge: what did ludovic achieve ? + (10:30:06) tschwinge: mcsim: As Richard says, symlink targets are always relative to the directory they're contained in. + (10:30:51) tschwinge: braunr: This Hydra/Nix (I wtill mix it all up) thing is kind of a package managing system. + (10:31:17) tschwinge: He has written scripts for bootstrapping a Hurd toolchain. + (10:31:26) braunr: oh ok + (10:31:27) mcsim: so, if I want to create link in cd, first I need to cd there? + (10:31:28) tschwinge: And then uses that to build a whole bootable image. + (10:31:36) mcsim: in foo* + (10:31:36) braunr: mcsim: just provide the right paths + (10:32:11) braunr: $ touch foo/bar + (10:32:14) braunr: $ ln -s bar foo/baz + (10:32:32) braunr: bar + (10:32:35) braunr: baz -> bar + +### defpager<a id="defpager81111"/> + + earlier: + <tschwinge>: 1. On every system there is a ``default pager'' (mach-defpager). That one is responsible + for all ``anonymous memory''. For example, when you do malloc(10 MiB), and then there is memory pressure, + this 10 MiB memory region is backed by the default pager, whose job then is it to provide the backing store for this. + <tschwinge>: This is what commonly would be known as a swap partition. + <tschwinge>: And this is also the way tmpfs works (as I understand it). + <tschwinge>: malloc(10 MiB) can also be mmap(MAP_ANONYMOUS, 10 MIB); that's the same, essentially. + <tschwinge>: Now, for ext2fs or any other disk-based file system, this is different: + <tschwinge>: The ext2fs translator implements its own backing store, namely it accesses the disk for storing + changed file content, or to read in data from disk if a new file is opened. + + ... + + (10:36:14) mcsim: who else uses defpager besides tmpfs and kernel? + (10:36:27) braunr: normally, nothing directly + (10:37:04) mcsim: than why tmpfs should use defpager? + (10:37:22) braunr: it's its backend + (10:37:28) braunr: backign store rather + (10:37:38) braunr: the backing store of most file systems are partitions + (10:37:44) braunr: tmpfs has none, it uses the swap space + (10:39:31) mcsim: if we allocate memory for tmpfs using vm_allocate, will it be able to use swap partition? + (10:39:56) braunr: it should + (10:40:27) braunr: vm_allocate just maps anonymous memory + (10:41:27) braunr: anonymous memory uses swap space as its backing store too + (10:43:47) braunr: but be aware that this part of the vm system is known to have deficiencies + (10:44:14) braunr: which is why all mach based implementations have rewritten their default pager + (10:45:11) mcsim: what kind of deficiencies? + (10:45:16) braunr: bugs + (10:45:39) braunr: and design issues, making anonymous memory fragmentation horrible + + ... + + (15:23:33) antrik: mcsim: vm_allocate doesn't return a memory object; so it can't be passed to clients for mmap() + (15:50:37) mcsim: antrik: I use vm_allocate in pager_read_page + (15:54:43) antrik: mcsim: well, that means that you have to actually implement a pager yourself + (15:56:10) antrik: also, when the kernel asks the pager to write back some pages, it expects the memory to become free. + if you are "paging" to ordinary anonymous memory, this doesn't happen; so I expect it to have a very bad effect + on system performance + (15:56:54) antrik: both can be avoided by just passing a real anonymous memory object, i.e. one provided by the defpager + (15:57:07) antrik: only problem is that the current defpager implementation can't really handle that... |