| Message ID | 20241211000447.1310181-3-d-tatianin@yandex-team.ru (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | overcommit: introduce mem-lock-onfault | expand |
On Wed, Dec 11, 2024 at 03:04:47AM +0300, Daniil Tatianin wrote: > Locking the memory without MCL_ONFAULT instantly prefaults any mmaped > anonymous memory with a write-fault, which introduces a lot of extra > overhead in terms of memory usage when all you want to do is to prevent > kcompactd from migrating and compacting QEMU pages. Add an option to > only lock pages lazily as they're faulted by the process by using > MCL_ONFAULT if asked. Looks good but some nitpicks below.. > > Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru> > --- > include/sysemu/sysemu.h | 1 + > migration/postcopy-ram.c | 4 ++-- > qemu-options.hx | 14 +++++++----- > system/globals.c | 1 + > system/vl.c | 46 ++++++++++++++++++++++++++++++++-------- > 5 files changed, 50 insertions(+), 16 deletions(-) > > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h > index 7ec419ce13..b6519c3c1e 100644 > --- a/include/sysemu/sysemu.h > +++ b/include/sysemu/sysemu.h > @@ -44,6 +44,7 @@ extern const char *keyboard_layout; > extern int old_param; > extern uint8_t *boot_splash_filedata; > extern bool enable_mlock; > +extern bool enable_mlock_onfault; > extern bool enable_cpu_pm; > extern QEMUClockType rtc_clock; > > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index 36ec6a3d75..8ff8c73a27 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -651,8 +651,8 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis) > mis->have_fault_thread = false; > } > > - if (enable_mlock) { > - if (os_mlock(false) < 0) { > + if (enable_mlock || enable_mlock_onfault) { > + if (os_mlock(enable_mlock_onfault) < 0) { > error_report("mlock: %s", strerror(errno)); > /* > * It doesn't feel right to fail at this point, we have a valid > diff --git a/qemu-options.hx b/qemu-options.hx > index dacc9790a4..6c8360e62e 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -4566,21 +4566,25 @@ SRST > ERST > > DEF("overcommit", HAS_ARG, QEMU_OPTION_overcommit, > - "-overcommit [mem-lock=on|off][cpu-pm=on|off]\n" > + "-overcommit [mem-lock=on|off|on-fault][cpu-pm=on|off]\n" > " run qemu with overcommit hints\n" > - " mem-lock=on|off controls memory lock support (default: off)\n" > + " mem-lock=on|off|on-fault controls memory lock support (default: off)\n" > " cpu-pm=on|off controls cpu power management (default: off)\n", > QEMU_ARCH_ALL) > SRST > -``-overcommit mem-lock=on|off`` > +``-overcommit mem-lock=on|off|on-fault`` > \ > ``-overcommit cpu-pm=on|off`` > Run qemu with hints about host resource overcommit. The default is > to assume that host overcommits all resources. > > Locking qemu and guest memory can be enabled via ``mem-lock=on`` > - (disabled by default). This works when host memory is not > - overcommitted and reduces the worst-case latency for guest. > + or ``mem-lock=on-fault`` (disabled by default). This works when > + host memory is not overcommitted and reduces the worst-case latency for > + guest. The on-fault option is better for reducing the memory footprint > + since it makes allocations lazy, but the pages still get locked in place > + once faulted by the guest or QEMU. Note that the two options are mutually > + exclusive. > > Guest ability to manage power state of host cpus (increasing latency > for other processes on the same host cpu, but decreasing latency for > diff --git a/system/globals.c b/system/globals.c > index 84ce943ac9..43501fe690 100644 > --- a/system/globals.c > +++ b/system/globals.c > @@ -35,6 +35,7 @@ enum vga_retrace_method vga_retrace_method = VGA_RETRACE_DUMB; > int display_opengl; > const char* keyboard_layout; > bool enable_mlock; > +bool enable_mlock_onfault; > bool enable_cpu_pm; > int autostart = 1; > int vga_interface_type = VGA_NONE; > diff --git a/system/vl.c b/system/vl.c > index 03819a80ef..4e2efd3ad4 100644 > --- a/system/vl.c > +++ b/system/vl.c > @@ -347,7 +347,7 @@ static QemuOptsList qemu_overcommit_opts = { > .desc = { > { > .name = "mem-lock", > - .type = QEMU_OPT_BOOL, > + .type = QEMU_OPT_STRING, > }, > { > .name = "cpu-pm", > @@ -792,8 +792,8 @@ static QemuOptsList qemu_run_with_opts = { > > static void realtime_init(void) > { > - if (enable_mlock) { > - if (os_mlock(false) < 0) { > + if (enable_mlock || enable_mlock_onfault) { IIUC it's still cleaner to make enable_mlock into an enum to be a tri-state. IOW, we could have two flags set now with the current patch when with things like: -overcommit mem-lock=on -overcommit mem-lock=on-fault > + if (os_mlock(enable_mlock_onfault) < 0) { > error_report("locking memory failed"); > exit(1); > } > @@ -3532,14 +3532,42 @@ void qemu_init(int argc, char **argv) > object_option_parse(optarg); > break; > case QEMU_OPTION_overcommit: > - opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"), > - optarg, false); > - if (!opts) { > + { > + const char *mem_lock_opt; > + > + opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"), > + optarg, false); > + if (!opts) { > + exit(1); > + } > + > + enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", enable_cpu_pm); > + > + mem_lock_opt = qemu_opt_get(opts, "mem-lock"); > + if (!mem_lock_opt) { > + break; > + } > + > + if (strcmp(mem_lock_opt, "on") == 0) { > + enable_mlock = true; > + break; > + } > + > + if (strcmp(mem_lock_opt, "off") == 0) { > + enable_mlock = false; > + enable_mlock_onfault = false; > + break; > + } > + > + if (strcmp(mem_lock_opt, "on-fault") == 0) { > + enable_mlock_onfault = true; > + break; > + } > + > + error_report("parameter 'mem-lock' expects one of " > + "'on', 'off', 'on-fault'"); Not the only one that open code this.. but still there're better references like net_client_parse() or monitor_parse() that we could follow. So would be good to put it into a function. Thanks, > exit(1); > } > - enable_mlock = qemu_opt_get_bool(opts, "mem-lock", enable_mlock); > - enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", enable_cpu_pm); > - break; > case QEMU_OPTION_compat: > { > CompatPolicy *opts_policy; > -- > 2.34.1 >
On 12/12/24 12:52 AM, Peter Xu wrote: > On Wed, Dec 11, 2024 at 03:04:47AM +0300, Daniil Tatianin wrote: >> Locking the memory without MCL_ONFAULT instantly prefaults any mmaped >> anonymous memory with a write-fault, which introduces a lot of extra >> overhead in terms of memory usage when all you want to do is to prevent >> kcompactd from migrating and compacting QEMU pages. Add an option to >> only lock pages lazily as they're faulted by the process by using >> MCL_ONFAULT if asked. > Looks good but some nitpicks below.. > >> Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru> >> --- >> include/sysemu/sysemu.h | 1 + >> migration/postcopy-ram.c | 4 ++-- >> qemu-options.hx | 14 +++++++----- >> system/globals.c | 1 + >> system/vl.c | 46 ++++++++++++++++++++++++++++++++-------- >> 5 files changed, 50 insertions(+), 16 deletions(-) >> >> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h >> index 7ec419ce13..b6519c3c1e 100644 >> --- a/include/sysemu/sysemu.h >> +++ b/include/sysemu/sysemu.h >> @@ -44,6 +44,7 @@ extern const char *keyboard_layout; >> extern int old_param; >> extern uint8_t *boot_splash_filedata; >> extern bool enable_mlock; >> +extern bool enable_mlock_onfault; >> extern bool enable_cpu_pm; >> extern QEMUClockType rtc_clock; >> >> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c >> index 36ec6a3d75..8ff8c73a27 100644 >> --- a/migration/postcopy-ram.c >> +++ b/migration/postcopy-ram.c >> @@ -651,8 +651,8 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis) >> mis->have_fault_thread = false; >> } >> >> - if (enable_mlock) { >> - if (os_mlock(false) < 0) { >> + if (enable_mlock || enable_mlock_onfault) { >> + if (os_mlock(enable_mlock_onfault) < 0) { >> error_report("mlock: %s", strerror(errno)); >> /* >> * It doesn't feel right to fail at this point, we have a valid >> diff --git a/qemu-options.hx b/qemu-options.hx >> index dacc9790a4..6c8360e62e 100644 >> --- a/qemu-options.hx >> +++ b/qemu-options.hx >> @@ -4566,21 +4566,25 @@ SRST >> ERST >> >> DEF("overcommit", HAS_ARG, QEMU_OPTION_overcommit, >> - "-overcommit [mem-lock=on|off][cpu-pm=on|off]\n" >> + "-overcommit [mem-lock=on|off|on-fault][cpu-pm=on|off]\n" >> " run qemu with overcommit hints\n" >> - " mem-lock=on|off controls memory lock support (default: off)\n" >> + " mem-lock=on|off|on-fault controls memory lock support (default: off)\n" >> " cpu-pm=on|off controls cpu power management (default: off)\n", >> QEMU_ARCH_ALL) >> SRST >> -``-overcommit mem-lock=on|off`` >> +``-overcommit mem-lock=on|off|on-fault`` >> \ >> ``-overcommit cpu-pm=on|off`` >> Run qemu with hints about host resource overcommit. The default is >> to assume that host overcommits all resources. >> >> Locking qemu and guest memory can be enabled via ``mem-lock=on`` >> - (disabled by default). This works when host memory is not >> - overcommitted and reduces the worst-case latency for guest. >> + or ``mem-lock=on-fault`` (disabled by default). This works when >> + host memory is not overcommitted and reduces the worst-case latency for >> + guest. The on-fault option is better for reducing the memory footprint >> + since it makes allocations lazy, but the pages still get locked in place >> + once faulted by the guest or QEMU. Note that the two options are mutually >> + exclusive. >> >> Guest ability to manage power state of host cpus (increasing latency >> for other processes on the same host cpu, but decreasing latency for >> diff --git a/system/globals.c b/system/globals.c >> index 84ce943ac9..43501fe690 100644 >> --- a/system/globals.c >> +++ b/system/globals.c >> @@ -35,6 +35,7 @@ enum vga_retrace_method vga_retrace_method = VGA_RETRACE_DUMB; >> int display_opengl; >> const char* keyboard_layout; >> bool enable_mlock; >> +bool enable_mlock_onfault; >> bool enable_cpu_pm; >> int autostart = 1; >> int vga_interface_type = VGA_NONE; >> diff --git a/system/vl.c b/system/vl.c >> index 03819a80ef..4e2efd3ad4 100644 >> --- a/system/vl.c >> +++ b/system/vl.c >> @@ -347,7 +347,7 @@ static QemuOptsList qemu_overcommit_opts = { >> .desc = { >> { >> .name = "mem-lock", >> - .type = QEMU_OPT_BOOL, >> + .type = QEMU_OPT_STRING, >> }, >> { >> .name = "cpu-pm", >> @@ -792,8 +792,8 @@ static QemuOptsList qemu_run_with_opts = { >> >> static void realtime_init(void) >> { >> - if (enable_mlock) { >> - if (os_mlock(false) < 0) { >> + if (enable_mlock || enable_mlock_onfault) { > IIUC it's still cleaner to make enable_mlock into an enum to be a > tri-state. IOW, we could have two flags set now with the current patch > when with things like: > > -overcommit mem-lock=on -overcommit mem-lock=on-fault Oh yeah good catch, that's a problem. >> + if (os_mlock(enable_mlock_onfault) < 0) { >> error_report("locking memory failed"); >> exit(1); >> } >> @@ -3532,14 +3532,42 @@ void qemu_init(int argc, char **argv) >> object_option_parse(optarg); >> break; >> case QEMU_OPTION_overcommit: >> - opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"), >> - optarg, false); >> - if (!opts) { >> + { >> + const char *mem_lock_opt; >> + >> + opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"), >> + optarg, false); >> + if (!opts) { >> + exit(1); >> + } >> + >> + enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", enable_cpu_pm); >> + >> + mem_lock_opt = qemu_opt_get(opts, "mem-lock"); >> + if (!mem_lock_opt) { >> + break; >> + } >> + >> + if (strcmp(mem_lock_opt, "on") == 0) { >> + enable_mlock = true; >> + break; >> + } >> + >> + if (strcmp(mem_lock_opt, "off") == 0) { >> + enable_mlock = false; >> + enable_mlock_onfault = false; >> + break; >> + } >> + >> + if (strcmp(mem_lock_opt, "on-fault") == 0) { >> + enable_mlock_onfault = true; >> + break; >> + } >> + >> + error_report("parameter 'mem-lock' expects one of " >> + "'on', 'off', 'on-fault'"); > Not the only one that open code this.. but still there're better references > like net_client_parse() or monitor_parse() that we could follow. So would > be good to put it into a function. > > Thanks, Yeah I'm not a fan of this solution to parsing, but I wasn't able to find better examples straight away so went with this. Will take a look at the places you've mentioned. Thanks! > >> exit(1); >> } >> - enable_mlock = qemu_opt_get_bool(opts, "mem-lock", enable_mlock); >> - enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", enable_cpu_pm); >> - break; >> case QEMU_OPTION_compat: >> { >> CompatPolicy *opts_policy; >> -- >> 2.34.1 >>
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h index 7ec419ce13..b6519c3c1e 100644 --- a/include/sysemu/sysemu.h +++ b/include/sysemu/sysemu.h @@ -44,6 +44,7 @@ extern const char *keyboard_layout; extern int old_param; extern uint8_t *boot_splash_filedata; extern bool enable_mlock; +extern bool enable_mlock_onfault; extern bool enable_cpu_pm; extern QEMUClockType rtc_clock; diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c index 36ec6a3d75..8ff8c73a27 100644 --- a/migration/postcopy-ram.c +++ b/migration/postcopy-ram.c @@ -651,8 +651,8 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis) mis->have_fault_thread = false; } - if (enable_mlock) { - if (os_mlock(false) < 0) { + if (enable_mlock || enable_mlock_onfault) { + if (os_mlock(enable_mlock_onfault) < 0) { error_report("mlock: %s", strerror(errno)); /* * It doesn't feel right to fail at this point, we have a valid diff --git a/qemu-options.hx b/qemu-options.hx index dacc9790a4..6c8360e62e 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4566,21 +4566,25 @@ SRST ERST DEF("overcommit", HAS_ARG, QEMU_OPTION_overcommit, - "-overcommit [mem-lock=on|off][cpu-pm=on|off]\n" + "-overcommit [mem-lock=on|off|on-fault][cpu-pm=on|off]\n" " run qemu with overcommit hints\n" - " mem-lock=on|off controls memory lock support (default: off)\n" + " mem-lock=on|off|on-fault controls memory lock support (default: off)\n" " cpu-pm=on|off controls cpu power management (default: off)\n", QEMU_ARCH_ALL) SRST -``-overcommit mem-lock=on|off`` +``-overcommit mem-lock=on|off|on-fault`` \ ``-overcommit cpu-pm=on|off`` Run qemu with hints about host resource overcommit. The default is to assume that host overcommits all resources. Locking qemu and guest memory can be enabled via ``mem-lock=on`` - (disabled by default). This works when host memory is not - overcommitted and reduces the worst-case latency for guest. + or ``mem-lock=on-fault`` (disabled by default). This works when + host memory is not overcommitted and reduces the worst-case latency for + guest. The on-fault option is better for reducing the memory footprint + since it makes allocations lazy, but the pages still get locked in place + once faulted by the guest or QEMU. Note that the two options are mutually + exclusive. Guest ability to manage power state of host cpus (increasing latency for other processes on the same host cpu, but decreasing latency for diff --git a/system/globals.c b/system/globals.c index 84ce943ac9..43501fe690 100644 --- a/system/globals.c +++ b/system/globals.c @@ -35,6 +35,7 @@ enum vga_retrace_method vga_retrace_method = VGA_RETRACE_DUMB; int display_opengl; const char* keyboard_layout; bool enable_mlock; +bool enable_mlock_onfault; bool enable_cpu_pm; int autostart = 1; int vga_interface_type = VGA_NONE; diff --git a/system/vl.c b/system/vl.c index 03819a80ef..4e2efd3ad4 100644 --- a/system/vl.c +++ b/system/vl.c @@ -347,7 +347,7 @@ static QemuOptsList qemu_overcommit_opts = { .desc = { { .name = "mem-lock", - .type = QEMU_OPT_BOOL, + .type = QEMU_OPT_STRING, }, { .name = "cpu-pm", @@ -792,8 +792,8 @@ static QemuOptsList qemu_run_with_opts = { static void realtime_init(void) { - if (enable_mlock) { - if (os_mlock(false) < 0) { + if (enable_mlock || enable_mlock_onfault) { + if (os_mlock(enable_mlock_onfault) < 0) { error_report("locking memory failed"); exit(1); } @@ -3532,14 +3532,42 @@ void qemu_init(int argc, char **argv) object_option_parse(optarg); break; case QEMU_OPTION_overcommit: - opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"), - optarg, false); - if (!opts) { + { + const char *mem_lock_opt; + + opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"), + optarg, false); + if (!opts) { + exit(1); + } + + enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", enable_cpu_pm); + + mem_lock_opt = qemu_opt_get(opts, "mem-lock"); + if (!mem_lock_opt) { + break; + } + + if (strcmp(mem_lock_opt, "on") == 0) { + enable_mlock = true; + break; + } + + if (strcmp(mem_lock_opt, "off") == 0) { + enable_mlock = false; + enable_mlock_onfault = false; + break; + } + + if (strcmp(mem_lock_opt, "on-fault") == 0) { + enable_mlock_onfault = true; + break; + } + + error_report("parameter 'mem-lock' expects one of " + "'on', 'off', 'on-fault'"); exit(1); } - enable_mlock = qemu_opt_get_bool(opts, "mem-lock", enable_mlock); - enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", enable_cpu_pm); - break; case QEMU_OPTION_compat: { CompatPolicy *opts_policy;
Locking the memory without MCL_ONFAULT instantly prefaults any mmaped anonymous memory with a write-fault, which introduces a lot of extra overhead in terms of memory usage when all you want to do is to prevent kcompactd from migrating and compacting QEMU pages. Add an option to only lock pages lazily as they're faulted by the process by using MCL_ONFAULT if asked. Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru> --- include/sysemu/sysemu.h | 1 + migration/postcopy-ram.c | 4 ++-- qemu-options.hx | 14 +++++++----- system/globals.c | 1 + system/vl.c | 46 ++++++++++++++++++++++++++++++++-------- 5 files changed, 50 insertions(+), 16 deletions(-)