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authorJoshua Branson <jbranso@fastmail.com>2018-11-07 10:32:38 -0500
committerSamuel Thibault <samuel.thibault@ens-lyon.org>2018-11-08 23:53:31 +0100
commit3e25a0fd194bbdb1838abb0a17832252eb03462a (patch)
tree42f11e17cf99aba0978047239fc15a4caa9c16a7 /open_issues/gnumach_memory_management.mdwn
parent1a8d5c728cc275f20d7f560e2760aa882c8ed502 (diff)
I am adding Richard's comment about mach's memory management issue to the open issues gnumach memory management page.
I also added a link to the 64-bit port on the 830MB RAM limit page.
Diffstat (limited to 'open_issues/gnumach_memory_management.mdwn')
-rw-r--r--open_issues/gnumach_memory_management.mdwn16
1 files changed, 14 insertions, 2 deletions
diff --git a/open_issues/gnumach_memory_management.mdwn b/open_issues/gnumach_memory_management.mdwn
index 8eb0cf8a..911c2b51 100644
--- a/open_issues/gnumach_memory_management.mdwn
+++ b/open_issues/gnumach_memory_management.mdwn
@@ -11,8 +11,6 @@ License|/fdl]]."]]"""]]
[[!tag open_issue_gnumach]]
-There is a [[!FF_project 266]][[!tag bounty]] on this task.
-
[[!toc]]
@@ -2389,3 +2387,17 @@ There is a [[!FF_project 266]][[!tag bounty]] on this task.
<braunr> well, there is also a locking error in the slab allocator,
although not a problem for a non preemptible kernel like gnumach
<braunr> non preemptible / uniprocessor
+
+## IRC freenode, #hurd, 2016-12-29
+
+ <braunr> i've identified a fundamental flaw with the default pager
+ <braunr> and actually, with mach in general i suppose
+ <braunr> i assumed that it was necessary to trust the server only
+ <braunr> that a server didn't need to trust its client
+ <braunr> but mach messages carry memory that is potentially mapped from unprivileged pagers
+ <braunr> which means faulting on that memory effectively makes the faulting process a client to the unprivileged pager
+ <braunr> and that's something that can happen to the default pager during heavy memory pressure
+ <braunr> in which case it deadlocks on itself because the copyout hangs on a fault, waiting for the unprivileged pager to provide the data
+ <braunr> (which it can't because of heavy memory pressure and because it's unprivileged, it's blocked, waiting until allocations resume)
+ <braunr> the pageout daemon will keep paging out to the default pager in the hope those pages get freed
+ <braunr> but sending to the default pager is now impossible because its map is locked on the never-ending fault