There are two justifications for making this change. The first is that
i386 emulation is typically for smaller machines where having a 1gb of
generated code is overkill for basic emulation. The second is the
propensity of self-modifying code (c.f. Doom/edit) utilised on i386
systems can trigger a rapid growth in invalidated and re-translated
buffers. This is seen in bug #283. Execution is still inefficient but
at least the host memory isn't so aggressively used up.

That said it's still really just a sticking plaster for user
convenience.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Thomas Huth <thuth@redhat.com>
Cc: 1896298@bugs.launchpad.net
---
 accel/tcg/translate-all.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index 640ff6e3e7..f442165674 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -951,9 +951,13 @@ static void page_lock_pair(PageDesc **ret_p1, tb_page_addr_t phys1,
  * Users running large scale system emulation may want to tweak their
  * runtime setup via the tb-size control on the command line.
  */
+#ifdef TARGET_I386
+#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB)
+#else
 #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (1 * GiB)
 #endif
 #endif
+#endif
 
 #define DEFAULT_CODE_GEN_BUFFER_SIZE \
   (DEFAULT_CODE_GEN_BUFFER_SIZE_1 < MAX_CODE_GEN_BUFFER_SIZE \
-- 
2.20.1

-- 
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https://bugs.launchpad.net/bugs/1896298

Title:
  TCG memory leak with FreeDOS 'edit'

Status in QEMU:
  Expired

Bug description:
  qemu trunk as of today leaks memory FAST when freedos' edit is
  running.

  To reproduce, download:

  https://www.ibiblio.org/pub/micro/pc-
  stuff/freedos/files/repositories/1.3/cdrom.iso

  Then run:

  $ qemu-system-i386 -cdrom cdrom.iso

  select your language then select "return to DOS", then type

  > edit

  it will consume memory at ~10MB/s

  This does NOT happen when adding -enable-kvm

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On 5/25/21 9:45 AM, Alex Bennée wrote:
> There are two justifications for making this change. The first is that
> i386 emulation is typically for smaller machines where having a 1gb of
> generated code is overkill for basic emulation. The second is the
> propensity of self-modifying code (c.f. Doom/edit) utilised on i386
> systems can trigger a rapid growth in invalidated and re-translated
> buffers. This is seen in bug #283. Execution is still inefficient but
> at least the host memory isn't so aggressively used up.
> 
> That said it's still really just a sticking plaster for user
> convenience.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> Cc: Thomas Huth <thuth@redhat.com>
> Cc: 1896298@bugs.launchpad.net
> ---
>   accel/tcg/translate-all.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 640ff6e3e7..f442165674 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -951,9 +951,13 @@ static void page_lock_pair(PageDesc **ret_p1, tb_page_addr_t phys1,
>    * Users running large scale system emulation may want to tweak their
>    * runtime setup via the tb-size control on the command line.
>    */
> +#ifdef TARGET_I386
> +#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB)
> +#else
>   #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (1 * GiB)
>   #endif
>   #endif
> +#endif
>   
>   #define DEFAULT_CODE_GEN_BUFFER_SIZE \
>     (DEFAULT_CODE_GEN_BUFFER_SIZE_1 < MAX_CODE_GEN_BUFFER_SIZE \
> 

I'm not thrilled, as it is ultra-hacky.

(1) I've got a re-org of this code out for review: 
https://patchew.org/QEMU/20210502231844.1977630-1-richard.henderson@linaro.org/

(2) I'm keen to reorg TCG such that it gets compiled once.  There's currently 
nothing standing in the way of that except work.  But this would introduce a 
use of a target-specific define for the first time into tcg/.  I guess I could 
leave the default sizing back in accel/tcg/ and pass in the default.

Other options?


r~

Alex Bennée <alex.bennee@linaro.org> writes:

> There are two justifications for making this change. The first is that
> i386 emulation is typically for smaller machines where having a 1gb of
> generated code is overkill for basic emulation. The second is the
> propensity of self-modifying code (c.f. Doom/edit) utilised on i386
> systems can trigger a rapid growth in invalidated and re-translated
> buffers. This is seen in bug #283. Execution is still inefficient but
> at least the host memory isn't so aggressively used up.
>
> That said it's still really just a sticking plaster for user
> convenience.

ping?


-- 
Alex Bennée