As you can see, this is strictly cache...
but you could be right, of course, but this is MORE than HALF of the
memory!!!.
Is there a way to get the kernel to try and flush the cache as much as
possible (if possible non-destructive?)
# xm list
Name ID Mem(MiB) VCPUs State Time(s)
Domain-0 0 4851 4 r----- 89515.8
xxxxxxxx 7 140 1 -b---- 16382.0
xxxxxxxx 26 140 1 -b---- 462.1
xxxxxxxx 3 268 1 -b---- 23890.8
xxxxxxxx 4 1038 1 r----- 878503.7
xxxxxxxx 22 268 1 -b---- 5406.6
xxxxxxxx 20 525 1 -b---- 5537.4
xxxxxxxx 5 140 1 -b---- 23039.8
xxxxxxxx 14 268 1 -b---- 10236.9
xxxxxxxx 6 268 1 -b---- 18234.1
# free
total used free shared buffers cached
Mem: 4967424 4947340 20084 0 153064 4262848
-/+ buffers/cache: 531428 4435996
Swap: 2104464 136 2104328
Sincerely,
Maarten
Op woensdag 27 juni 2007 14:37, schreef Petersson, Mats:
> > -----Original Message-----
> > From: Maarten Vanraes [mailto:maarten@xxxxx]
> > Sent: 27 June 2007 13:28
> > To: xen-users@xxxxxxxxxxxxxxxxxxx
> > Cc: Petersson, Mats; Arie Goldfeld
> > Subject: Re: [Xen-users] out of memory with xen
> >
> > well if that is so, how can i free the cache?
> >
> > I've read that an Out Of Memory kernel event should try to
> > free as much cache
> > as possible...
>
> It may be that it's not cache that occupies the memory, perhaps?
>
> The "balloon" method that Xen uses for assigning one domains memory to
> another domain works this way (simplisticly):
> - On the "giving up memory" domain, it allocates (in a kernel "ballon
> driver") memory.
> - On the "receiving" domain, the memory is added to it's list of memory
> available.
>
> If it takes too long to find free memory, it will give up (in fact, for
> the release version of Xen, I believe if it "fails to get the requested
> memory" it will stop allocation, even if it's still able to allocate
> more memory - there's a patch in unstable that allows it to continue as
> long as it's making progress, even if it's slower than "instant".
>
> The problem here is that the cache may be "dirty", meaning that data in
> the cache has to be written to the disk before it can be re-used for
> other purposes. This in turn means that if you suddenly need a large
> amount of space, it can take several seconds to clean up the dirty pages
> in the caceh and allow them to be used.
>
> The other problem with giving Dom0 a huge amount of space and then
> "ballon" it off to other domains is that the memory allocations for
> certain data structures in the kernel are done as proportion of total
> memory, so some static data structure may be 3% of the total memory for
> example. There are several different allocations made in this way. So if
> you try to shrink Dom0 by a large amount, it may run out of memory,
> despite the fact that it would be perfectly fine to run Dom0 on the
> memory size it's been shrunk to (because the smaller size doesn't have
> as large proportion used by these proportional data structures).
>
> --
> Mats
>
> > Sincerely,
> >
> > Maarten
> >
> > Op woensdag 27 juni 2007 11:36, schreef Petersson, Mats:
> > > > -----Original Message-----
> > > > From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> > > > [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> > > > Maarten Vanraes
> > > > Sent: 27 June 2007 10:28
> > > > To: xen-users@xxxxxxxxxxxxxxxxxxx
> > > > Cc: Arie Goldfeld
> > > > Subject: Re: [Xen-users] out of memory with xen
> > > >
> > > > wont the caching require more memory anyway, and won't it
> > > > start to swap and
> > > > ultimately start to kill processes?
> > >
> > > No, because the caches are used from "free memory", so if you don't
> > > start out with much memory, the cache won't grow so large.
> >
> > Essentially,
> >
> > > the principle is that if you have some memory that isn't
> >
> > being used for
> >
> > > "anything", it can be used as cache.
> > >
> > > --
> > > Mats
> > >
> > > > Sincerely,
> > > >
> > > > Op woensdag 27 juni 2007 10:04, schreef Arie Goldfeld:
> > > > > You could use dom0_mem grub parameter to restrict the size
> > > >
> > > > of RAM dom0
> > > >
> > > > > occupies; it looks somethings like this:
> > > > >
> > > > > kernel /xen.gz dom0_mem=400000
> > > > >
> > > > > On 6/27/07, Maarten Vanraes <maarten@xxxxx> wrote:
> > > > > > our xen server has 8GB RAM.
> > > > > >
> > > > > > dom0 is not doing anything, but has cached about 4.9GB of
> > > >
> > > > the ram, which
> > > >
> > > > > > results in failure to create new hosts.
> > > > > >
> > > > > > i'm using file based storage, and i've read in the
> > > >
> > > > mailing list archive
> > > >
> > > > > > about
> > > > > > the problem being /dev/loop being used internally in xen.
> > > > > >
> > > > > > is there a way to flush this cache? is there already
> >
> > a fix for the
> >
> > > > > > extreme caching of these devices?
> > > > > >
> > > > > > I see that lvm is a possible workaround, but i'd rather
> > > >
> > > > not do this right
> > > >
> > > > > > now.
> > > > > > Plus it is not so easy to convert 500GB into lvm...
> > > > > >
> > > > > > any solutions yet?
> > > > > >
> > > > > > Sincerely,
> > > > > > --
> > > > > > Maarten Vanraes
> > > > > > BA NV: IT & Security
> > > > > >
> > > > > > _______________________________________________
> > > > > > Xen-users mailing list
> > > > > > Xen-users@xxxxxxxxxxxxxxxxxxx
> > > > > > http://lists.xensource.com/xen-users
> > > >
> > > > --
> > > > Maarten Vanraes
> > > > BA NV: IT & Security
> > > >
> > > > _______________________________________________
> > > > Xen-users mailing list
> > > > Xen-users@xxxxxxxxxxxxxxxxxxx
> > > > http://lists.xensource.com/xen-users
> > >
> > > _______________________________________________
> > > Xen-users mailing list
> > > Xen-users@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-users
> >
> > --
> > Maarten Vanraes
> > BA NV: IT & Security
--
Maarten Vanraes
BA NV: IT & Security
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