From: "Daniel P. Berrangé" <berrange@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: fam@euphon.net, richard.henderson@linaro.org,
qemu-devel@nongnu.org,
Christian Ehrhardt <christian.ehrhardt@canonical.com>,
f4bug@amsat.org, cota@braap.org,
Paolo Bonzini <pbonzini@redhat.com>,
aurelien@aurel32.net, Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH v1 5/5] accel/tcg: better handle memory constrained systems
Date: Fri, 17 Jul 2020 16:00:52 +0100 [thread overview]
Message-ID: <20200717150052.GK244185@redhat.com> (raw)
In-Reply-To: <87h7u6ur70.fsf@linaro.org>
On Fri, Jul 17, 2020 at 03:55:15PM +0100, Alex Bennée wrote:
>
> Daniel P. Berrangé <berrange@redhat.com> writes:
>
> > On Fri, Jul 17, 2020 at 11:51:39AM +0100, Alex Bennée 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: 600e17b261
> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> >> Cc: BALATON Zoltan <balaton@eik.bme.hu>
> >> Cc: Christian Ehrhardt <christian.ehrhardt@canonical.com>
> >> ---
> >> 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..2ff0ba6d19b 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 && phys_mem < (2 * DEFAULT_CODE_GEN_BUFFER_SIZE)) {
> >> + tb_size = phys_mem / 4;
> >> + } else {
> >> + tb_size = DEFAULT_CODE_GEN_BUFFER_SIZE;
> >> + }
> >
> > I'm not convinced this is going to work when running QEMU inside a
> > container environment with RAM cap, because the physmem level is
> > completely unrelated to the RAM the container is permitted to actually
> > use in practice. ie host has 32 GB of RAM, but the container QEMU is
> > in only has 1 GB permitted.
>
> What will happen when the mmap happens? Will a capped container limit
> the attempted mmap? I would hope the container case at least gave
> different feedback than a "silent" OOM.
IIRC it should trigger the OOM killer on process(s) within the container.
Regards,
Daniel
--
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prev parent reply other threads:[~2020-07-17 15:05 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 10:51 [PATCH v1 0/5] candidate fixes for 5.1-rc1 (shippable, semihosting, OOM tcg) Alex Bennée
2020-07-17 10:51 ` [PATCH v1 1/5] shippable: add one more qemu to registry url Alex Bennée
2020-07-17 19:41 ` Philippe Mathieu-Daudé
2020-07-17 10:51 ` [PATCH v1 2/5] semihosting: defer connect_chardevs a little more to use serialx Alex Bennée
2020-07-17 17:41 ` Richard Henderson
2020-07-17 10:51 ` [PATCH v1 3/5] semihosting: don't send the trailing '\0' Alex Bennée
2020-07-17 17:47 ` Richard Henderson
2020-07-17 10:51 ` [PATCH v1 4/5] util: add qemu_get_host_physmem utility function Alex Bennée
2020-07-17 13:32 ` BALATON Zoltan
2020-07-17 14:24 ` Christian Ehrhardt
2020-07-17 18:00 ` Richard Henderson
2020-07-21 13:50 ` Alex Bennée
2020-07-17 18:05 ` Richard Henderson
2020-07-21 15:58 ` Alex Bennée
2020-07-17 10:51 ` [PATCH v1 5/5] accel/tcg: better handle memory constrained systems Alex Bennée
2020-07-17 14:23 ` Christian Ehrhardt
2020-07-17 14:39 ` Daniel P. Berrangé
2020-07-17 14:55 ` Alex Bennée
2020-07-17 15:00 ` Daniel P. Berrangé [this message]
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