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

[Robert Foley]

Reviewed-by: Robert Foley <robert.foley@linaro.org>


On Fri, 24 Jul 2020 at 02:49, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> 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
>
>