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+[[!meta copyright="Copyright © 2011, 2013 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_documentation open_issue_gnumach]]
+
+
+# IRC, freenode, #hurd, 2011-01-06
+
+    <antrik> hm, odd... vmstat tells me that ~500 MiB of RAM are in use; but
+      the sum of all RSS is <300 MiB... what's the rest?
+    <braunr> kernel memory ?
+    <braunr> the zone allocator maybe
+    <braunr> or the page cache simply
+    <antrik> braunr: which page cache? AIUI, caches are implemented by the
+      individual filesystem servers -- in which case any memory used by them
+      should show up in RSS
+    <antrik> also, gnumach is listed among other tasks, so I'd assume the
+      kernel memery also to be accounted for
+    <braunr> antrik: no, the kernel maintains a page cache, very similar to
+      what is done in Linux, and almost the same as in FreeBSD
+    <braunr> the file system servers are just backing stores
+    <braunr> the RSS for the gnumach tasks only includes kernel memory
+    <braunr> I don't think the page cache is accounted for
+    <braunr> because it's not really kernel memory, it's a cache of user space
+      memory
+    <antrik> apparently my understanding of Mach paging is still (or again?)
+      rather incomplete :-(
+    <antrik> BTW, is there any way to find out how much anonymous memory a
+      process is using? the "virtual" includes discardable mappings, and is
+      thus not very helpful...
+    <antrik> (that applies to Linux as well though)
+    <braunr> can you provide an example of the output of vmstat please ?
+    <braunr> I don't have a Hurd VM near me
+    <antrik> olaf@alien:~$ vmstat
+    <antrik> pagesize:          4K
+    <antrik> size:            501M
+    <antrik> free:           6.39M
+    <antrik> active:          155M
+    <antrik> inactive:        310M
+    <antrik> wired:          29.4M
+    <antrik> zero filled:    15.3G
+    <antrik> reactivated:     708M
+    <antrik> pageins:        3.43G
+    <antrik> pageouts:       1.55G
+    <antrik> page faults: 26844574
+    <antrik> cow faults:   3736174
+    <antrik> memobj hit ratio: 92%
+    <antrik> swap size:       733M
+    <antrik> swap free:       432M
+    <antrik> interesting... closing a single screen window temporarily raises
+      the "free" value by almost 10 MB
+    <antrik> I guess bash is rather hungry nowadays ;-)
+    <braunr> antrik: I guess the only way is using pmap or looking into
+      /proc/<pid>/maps
+    <braunr> but it won't give you the amount of physical memory used by
+      anonymous mappings
+    <antrik> nah, I don't even want that... just like to know how much memory
+      (RAM+swap) a process is really using
+    <braunr> antrik: then the RSS field is what you want
+    <antrik> OTOH, anonymous doesn't include program code or other actively
+      used mappings... so not very useful either
+    <antrik> nah, RSS doesn't count anything that is in swap
+    <braunr> well
+    <braunr> don't you have a SWAP column ?
+    <braunr> hm
+    <braunr> i guess not
+    <braunr> antrik: why do you say it doesn't include other actively used
+      mappings ?
+    <braunr> antrik: and the inclusion of program code also depends on the
+      implementation of the ELF handler
+    <braunr> I don't know how the hurd does that, but some ELF loaders use
+      anonymous memory for the execution view
+    <antrik> well, if a program maps a data file, and regularily accesses parts
+      of the file, they won't occupy physical RAM all the time (and show up in
+      RSS), but they are not anonymous mappings. similar to program code
+    <braunr> then this anonymous memory is shared by all processes using that
+      code
+    <antrik> oh, interesting
+    <antrik> is it really a completely distinct mapping, rather than just COW?
+    <braunr> the first is
+    <braunr> others are COW
+    <antrik> so if a program loads 200 MB of libraries, they are all read in on
+      startup, and occupy RAM or swap subsequently, even if most of the code is
+      never actually run?...
+    <kilobug> library code should be backed by the library file on disk, not be
+      swap
+    <braunr> depends on the implementation
+    <braunr> I guess most use the file system backend
+    <braunr> but in the Hurd, ext2fs.static and ld.so.1 use anonymous memory
+    <braunr> (that's the case for another reason, still, I don't think the
+      report in top/ps clearly indicates that fact)
+    <kilobug> braunr: yeah for bootstrapping issues, makes sense
+    <braunr> it may also depends on the pic/pie options used when building
+      libraries
+
+
+# IRC, freenode, #hurd, 2011-07-24
+
+    < braunr> the panic is probably due to memory shortage
+    < braunr> so as antrik suggested, use more swap
+    < antrik> gg0: you could run "vmstat 1" in another terminal to watch memory
+      usage
+    < antrik> that way we will know for sure whether it's related
+    < braunr> antrik: it's trickier than that
+    < braunr> it depends if the zones used are pageable
+    < antrik> braunr: well, if it's a zone map exhaustion, then the swap size
+      won't change anything?...
+    < braunr> antrik: in this case no, but if the zone is pageable and the
+      pager (backing anonymous memory) refuses to create memory because it
+      estimates it's full (all swap space is reserved), it will fail to
+    < braunr> too
+    < braunr> but i don't think there are much pageable zones in the kernel
+    < antrik> yes, but in that case we can see the exhaustion in vmstat :-)
+    < braunr> many*
+    < braunr> i'm not sure
+    < braunr> reserved swap space doesn't mean it's used
+    < braunr> that's one of the major changes in freebsd 4 or 5 i was
+      mentioning
+    < antrik> if it's reserved, it wouldn't show up as "free", would it?...
+    < braunr> (btw, it's also what makes anonymous memory merging so hard)
+    < braunr> yes it would
+    < braunr> well, it could, i'm not sure
+    < braunr> anonymous memory is considered as a file
+    < braunr> one big file filled with zeroes, which is the swap partition
+    < braunr> when you allocate pageable anonymous memory, a part of this
+      "file" is reserved
+    < braunr> but i don't know if the reported number if the reserved
+      (allocated) space, or used (actually containing data)
+    < braunr> is*
+    < braunr> i also suspect wired allocations can fail because of a full swap
+      (because the kernel is unable to make free pages)
+    < braunr> in this case vmstat will show it
+    < antrik> what does it matter whether there is data there or not? if it's
+      reserved, it's not free. if it behaves differently, I'd consider that a
+      serious bug
+    < braunr> maybe the original developers intended to monitor its actual
+      usage
+    < braunr> antrik: i've just checked how the free count gets updated, and it
+      looks like it is on both seqnos_memory_object_data_initialize and
+      seqnos_memory_object_data_write
+    < braunr> antrik: so i guess reserved memory is accounted for
+
+
+# IRC, freenode, #hurd, 2013-01-12
+
+    <tschwinge> darnassus linking clang: 600 MiB swap in use and 22 MiB RAM
+      free, of 2 GiB.  But ps shows a RSS of just 100 MiB, huh?
+    <tschwinge> Getting "better": near the end of the link, nearly 1 GiB swap
+      in use, and 200 KiB (!) RAM free.
+    <sobhan> can hurd have more than 1GB of ram ?
+    <tschwinge> And then it completed; 75 MiB swap in use, and 1.2 GiB RAM
+      free.
+    <braunr> tschwinge: unless i'm mistaken, mach uses the legacy "swapping"
+      bsd mechanism 
+    <braunr> tschwinge: i.e. when it swaps a process, it swaps all of it
+    <braunr> tschwinge: the rest is probably one big anonymous vm object
+      containing the process space
+    <braunr> cached objects aren't currently well accounted
+    <braunr> (well, since youpi got my page cache patches in, they are, but
+      procfs isn't yet modified to report them)
+    <braunr> tschwinge: right, i'm currently looking at the machine and it
+      doesn't add up, i suppoe there are some big files still in the cache
+    <braunr> ah, git packed objects :p
+    <braunr> and a few llvm .a/.so/executable files too
+    <braunr> and since they're probably targets, they're built last, which
+      explains why they're retained in the cache for a while
+
+[[microkernel/mach/message/msgh_id]] (why on *that* page?).