Transcendent memory ("tmem") for Xen.

Tmem, when called from a tmem-capable (paravirtualized) guest, makes
use of otherwise unutilized ("fallow") memory to create and manage
pools of pages that can be accessed from the guest either as
"ephemeral" pages or as "persistent" pages.  In either case, the pages
are not directly addressible by the guest, only copied to and fro via
the tmem interface.  Ephemeral pages are a nice place for a guest to
put recently evicted clean pages that it might need again; these pages
can be reclaimed synchronously by Xen for other guests or other uses.
Persistent pages are a nice place for a guest to put "swap" pages to
avoid sending them to disk.  These pages retain data as long as the
guest lives, but count against the guest memory allocation.

Tmem pages may optionally be compressed and, in certain cases, can be
shared between guests.  Tmem also handles concurrency nicely and
provides limited QoS settings to combat malicious DoS attempts.
Save/restore and live migration support is not yet provided.

Tmem is primarily targeted for an x86 64-bit hypervisor.  On a 32-bit
x86 hypervisor, it has limited functionality and testing due to
limitations of the xen heap.  Nearly all of tmem is
architecture-independent; three routines remain to be ported to ia64
and it should work on that architecture too.  It is also structured to
be portable to non-Xen environments.

Tmem defaults off (for now) and must be enabled with a "tmem" xen boot
option (and does nothing unless a tmem-capable guest is running).  The
"tmem_compress" boot option enables compression which takes about 10x
more CPU but approximately doubles the number of pages that can be
stored.

Tmem can be controlled via several "xm" commands and many interesting
tmem statistics can be obtained.  A README and internal specification
will follow, but lots of useful prose about tmem, as well as Linux
patches, can be found at http://oss.oracle.com/projects/tmem .

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
index 7a5a5ab5d7..a952f0700d 100644
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -67,12 +67,14 @@ void _read_unlock_irqrestore(rwlock_t *lock, unsigned long flags);
 void _write_lock(rwlock_t *lock);
 void _write_lock_irq(rwlock_t *lock);
 unsigned long _write_lock_irqsave(rwlock_t *lock);
+int _write_trylock(rwlock_t *lock);
 
 void _write_unlock(rwlock_t *lock);
 void _write_unlock_irq(rwlock_t *lock);
 void _write_unlock_irqrestore(rwlock_t *lock, unsigned long flags);
 
 int _rw_is_locked(rwlock_t *lock);
+int _rw_is_write_locked(rwlock_t *lock);
 
 #define spin_lock(l)                  _spin_lock(l)
 #define spin_lock_irq(l)              _spin_lock_irq(l)
@@ -110,11 +112,13 @@ int _rw_is_locked(rwlock_t *lock);
 #define write_lock(l)                 _write_lock(l)
 #define write_lock_irq(l)             _write_lock_irq(l)
 #define write_lock_irqsave(l, f)      ((f) = _write_lock_irqsave(l))
+#define write_trylock(l)              _write_trylock(l)
 
 #define write_unlock(l)               _write_unlock(l)
 #define write_unlock_irq(l)           _write_unlock_irq(l)
 #define write_unlock_irqrestore(l, f) _write_unlock_irqrestore(l, f)
 
 #define rw_is_locked(l)               _rw_is_locked(l)
+#define rw_is_write_locked(l)         _rw_is_write_locked(l)
 
 #endif /* __SPINLOCK_H__ */