add mailinglist scraper results

1 files changed, 73 insertions, 0 deletions

diff --git a/mailinglist/output_launchpad/1609968 b/mailinglist/output_launchpad/1609968
new file mode 100644
index 00000000..109a8fcf
--- /dev/null
+++ b/mailinglist/output_launchpad/1609968
@@ -0,0 +1,73 @@
+"cannot set up guest memory" b/c no automatic clearing of Linux' cache
+
+Version: qemu-2.6.0-1
+Kernel: 4.4.13-1-MANJARO
+Full script (shouldn't matter though): https://pastebin.com/Hp24PWNE
+
+Problem:
+When host has been up and used for a while cache has been filled as much that guest can't be started without droping caches.
+
+Expected behavior:
+Qemu should be able to request as much Memory as it needs and cause Linux to drop cache pages if needed. A user shouldn't be required to have to come to this conclusion and having to drop caches to start Qemu with the required amount of memory.
+
+My fix:
+Following command (as root) required before qemu start:
+# sync && echo 3 > /proc/sys/vm/drop_caches
+
+Example:
+$ sudo qemu.sh -m 10240 && echo success || echo failed
+qemu-system-x86_64: cannot set up guest memory 'pc.ram': Cannot allocate memory
+failed
+$ free
+              total        used        free      shared  buff/cache   available
+Mem:       16379476     9126884     3462688      148480     3789904     5123572
+Swap:             0           0           0
+$ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
+$ free
+              total        used        free      shared  buff/cache   available
+Mem:       16379476     1694528    14106552      149772      578396    14256428
+Swap:             0           0           0
+$ sudo qemu.sh -m 10240  && echo success || echo failed
+success
+
+Hi Celmor,
+  That shouldn't happen! QEMU's allocation of memory is pretty normal, so really the question is for the kernel guys.
+  Having chatted to a collague, two questions:
+     a) Does it still happen if you set /proc/sys/vm/overcommit_memory to 1?
+     b) What filesystem are you using (some have different behaviour when dealing with the caches).
+
+@dgilbert-h / Dr. David Alan Gilbert
+Thanks for your answer.
+
+b)
+Mounted/used block devices:
+NAME    MOUNTPOINT TYPE  FSTYPE
+sda                disk  crypto_LUKS
+└─Data1            crypt zfs_member
+├─sdb5  /          part  ext4
+└─sdb6  /boot      part  vfat
+sdd                disk  crypto_LUKS
+└─Data2            crypt zfs_member
+ZFS file system for extra space, also ZFS is the reason I'm not running the latest kernel...
+
+a)
+$ free
+              total        used        free      shared  buff/cache   available
+Mem:       16379476     7879216     1867196      188180     6633064     3587620
+Swap:             0           0           0
+$ qemu.sh -m 10240 && echo success || echo failed
+qemu-system-x86_64: cannot set up guest memory 'pc.ram': Cannot allocate memory
+failed
+$ sudo sh -c 'echo 1 > /proc/sys/vm/overcommit_memory'
+$ qemu.sh -m 10240 && echo success || echo failed
+success
+
+So setting /proc/sys/vm/overcommit_memory to 1 works, so I guess I'm gonna need to execute
+sudo sh -c 'echo 1 > /proc/sys/vm/overcommit_memory'
+at start of my qemu.sh script instead of the 'drop_caches' part.
+I still think the kernel should do whatever function overcommit_memory is for automatically, bit it seams to be the fault of the kernel of my distribution then, thanks for your help.
+
+Thanks Celmor; that might be one for the zfs guys then if that's what's holding onto the caches; I suspect their caching is a bit different from the rest of the Linux filesystems.
+
+I'm going to close this as 'invalid' because I'm pretty sure this isn't a qemu bug; the kernel should be giving us the RAM we asked for if it's got it.
+