[PATCH v3 06/16] accel/tcg: better handle memory constrained systems

[Alex Bennée]

It turns out there are some 64 bit systems that have relatively low
amounts of physical memory available to them (typically CI system).
Even with swapping available a 1GB translation buffer that fills up
can put the machine under increased memory pressure. Detect these low
memory situations and reduce tb_size appropriately.

Fixes: 600e17b2615 ("accel/tcg: increase default code gen buffer size for 64 
bit")
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: BALATON Zoltan <balaton@eik.bme.hu>
Cc: Christian Ehrhardt <christian.ehrhardt@canonical.com>

---
v3
  - use slightly tweak the logic to taper off more nicely
---
 accel/tcg/translate-all.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index 2afa46bd2b1..2d83013633b 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -976,7 +976,12 @@ static inline size_t size_code_gen_buffer(size_t tb_size)
 {
     /* Size the buffer.  */
     if (tb_size == 0) {
-        tb_size = DEFAULT_CODE_GEN_BUFFER_SIZE;
+        size_t phys_mem = qemu_get_host_physmem();
+        if (phys_mem == 0) {
+            tb_size = DEFAULT_CODE_GEN_BUFFER_SIZE;
+        } else {
+            tb_size = MIN(DEFAULT_CODE_GEN_BUFFER_SIZE, phys_mem / 8);
+        }
     }
     if (tb_size < MIN_CODE_GEN_BUFFER_SIZE) {
         tb_size = MIN_CODE_GEN_BUFFER_SIZE;
-- 
2.20.1