Re: 8.2-PRERELEASE: live deadlock,
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On Sat, Jan 08, 2011 at 10:29:09PM +0300, Lev Serebryakov wrote:
> Hello, Kostik.
> You wrote 8 =D1=CE=D7=C1=D2=D1 2011 =C7., 22:02:32:
>=20
>=20
> > There is some weird backtrace at the pid 20, what is g_raid5 ?
> It is geom_raid5, with two threads -- working one and one for
> processing finished bios.
>=20
> > If I am guessing right, this creature has a classic deadlock when=20
> > bio processing requires memory allocation. It seems that tid 100079
> tid 100079 sleep in waiting for some data in queue.
>=20
> > is sleeping not even due to the free page shortage, but due to address
> > space exhaustion. As result, read/write requests are stalled.
> tid 100078 sleep in malloc(). But geom_raid5 never ever allocate
> more than 128MiB of memory and it is 64bit system with huge amount of
> kmem_size/kmem_size_max...
>=20
> How could I explore allocation (like vmstat -m) from kdb to be sure,
> it doesn't allocated more?
Use "show uma" and "show malloc" from ddb.
>=20
> And, if it is "classic deadlock" is here any "classical" solution to
> it?
Do not allocate during bio processing.
>=20
> Really, I'm maintainer of geom_raid5 now, so I need fix this
> deadlock, but I don't really understand, why does it occur? I've
> hit panic with "kernel memory exhausted" symptoms when module allocate
> too much, but not deadlock :(
Hm, I missed the kmem_back() in the stack. Yes, the thread is waiting for p=
age
allocation.
>=20
> > Then, syncer is blocked waiting for some physical buffer (look at tid
> > 100075), owning the vnode lock. Other processes also wait for the
> > locked buffers, etc.
>=20
> > So my belief is that this is plain driver (g_raid5, whatever is it)
> > i/o loss. Try the same load without it.
> I can not, because all data is on this GEOM :)
>=20
> --=20
> // Black Lion AKA Lev Serebryakov <lev@serebryakov.spb.ru>
>=20
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