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Fri, 17 Jul 2020 15:00:55 +0000 (UTC) Date: Fri, 17 Jul 2020 16:00:52 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Alex =?utf-8?Q?Benn=C3=A9e?= Subject: Re: [PATCH v1 5/5] accel/tcg: better handle memory constrained systems Message-ID: <20200717150052.GK244185@redhat.com> References: <20200717105139.25293-1-alex.bennee@linaro.org> <20200717105139.25293-6-alex.bennee@linaro.org> <20200717143908.GI244185@redhat.com> <87h7u6ur70.fsf@linaro.org> MIME-Version: 1.0 In-Reply-To: <87h7u6ur70.fsf@linaro.org> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/17 05:27:47 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: fam@euphon.net, richard.henderson@linaro.org, qemu-devel@nongnu.org, Christian Ehrhardt , f4bug@amsat.org, cota@braap.org, Paolo Bonzini , aurelien@aurel32.net, Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jul 17, 2020 at 03:55:15PM +0100, Alex Bennée wrote: > > Daniel P. Berrangé 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 > >> Cc: BALATON Zoltan > >> Cc: Christian Ehrhardt > >> --- > >> 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 -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|