On Fri, Jul 17, 2020 at 4:07 PM Christian Ehrhardt <
christian.ehrha...@canonical.com> wrote:
> Since v5.0.0 and 600e17b2 "accel/tcg: increase default code gen buffer
> size for 64 bit" in particular qemu with TCG regularly gets OOM Killed
> on small hosts.
>
> The former 47a2def4 "accel/tcg: remove link between guest ram and TCG
> cache size" removed the link to guest size which is right, but at least
> some connection to the host size needs to be retained to avoid growing
> out of control on common CI setups which run at 1-2G host sizes.
>
> The lower value of 1/8th of the host memory size and the default (of
> currently 1G) will be taken to initialize the TB. There already is a
> Min/Max check in place to not reach ridiculously small values.
>
> Fixes: 600e17b2
>
Just found "[PATCH v1 0/5] candidate fixes for 5.1-rc1 (shippable,
semihosting, OOM tcg)"
which was submitted while I was prepping this one (this is a busy day since
I'll be off for a week).
Please ignore this patch here and give the series of Alex a look as it is
the more advanced version :-).
> Signed-off-by: Christian Ehrhardt <christian.ehrha...@canonical.com>
> ---
> accel/tcg/translate-all.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 2afa46bd2b..ffcd67060e 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -977,6 +977,29 @@ 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;
> + /*
> + * A static default of 1G turned out to break (OOM Kill) many
> common
> + * CI setups that run at 1-2G Host memory size.
> + * At the same time the former default of ram_size/4 wasted
> performance
> + * on large host systems when running small guests.
> + * Common CI guest sizes are 0.5-1G which meant ~128M-256M TB
> size.
> + * A Default of 1/8th of the host size will get small hosts a
> + * similar TB size than they had prior to v5.0 and common bare
> metal
> + * systems (>=8G) the new 1G default that was set in v5.0
> + */
> +#if defined _SC_PHYS_PAGES && defined _SC_PAGESIZE
> + {
> + unsigned long max = DEFAULT_CODE_GEN_BUFFER_SIZE;
> + double pages = (double)sysconf(_SC_PHYS_PAGES);
> +
> + if (pages > 0 && pagesize > 0) {
> + max = (unsigned long)((pages * qemu_real_host_page_size)
> / 8);
> + }
> + if (max < DEFAULT_CODE_GEN_BUFFER_SIZE) {
> + tb_size = max;
> + }
> + }
> +#endif
> }
> if (tb_size < MIN_CODE_GEN_BUFFER_SIZE) {
> tb_size = MIN_CODE_GEN_BUFFER_SIZE;
> --
> 2.27.0
>
>
--
Christian Ehrhardt
Staff Engineer, Ubuntu Server
Canonical Ltd
