From 13057e064a3edae7abf9ca2c207cdf48b82c5aad Mon Sep 17 00:00:00 2001 From: Daniil Tatianin Date: Wed, 12 Feb 2025 17:39:20 +0300 Subject: overcommit: introduce mem-lock=on-fault 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. Reviewed-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Peter Xu Signed-off-by: Daniil Tatianin Link: https://lore.kernel.org/r/20250212143920.1269754-5-d-tatianin@yandex-team.ru Signed-off-by: Peter Xu --- system/vl.c | 34 +++++++++++++++++++++++++++------- 1 file changed, 27 insertions(+), 7 deletions(-) (limited to 'system/vl.c') diff --git a/system/vl.c b/system/vl.c index 2895824c1a..3c0fa2ff64 100644 --- a/system/vl.c +++ b/system/vl.c @@ -351,7 +351,7 @@ static QemuOptsList qemu_overcommit_opts = { .desc = { { .name = "mem-lock", - .type = QEMU_OPT_BOOL, + .type = QEMU_OPT_STRING, }, { .name = "cpu-pm", @@ -797,7 +797,7 @@ static QemuOptsList qemu_run_with_opts = { static void realtime_init(void) { if (should_mlock(mlock_state)) { - if (os_mlock(false) < 0) { + if (os_mlock(is_mlock_on_fault(mlock_state)) < 0) { error_report("locking memory failed"); exit(1); } @@ -1878,7 +1878,7 @@ static void object_option_parse(const char *str) static void overcommit_parse(const char *str) { QemuOpts *opts; - bool enable_mlock; + const char *mem_lock_opt; opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"), str, false); @@ -1886,11 +1886,31 @@ static void overcommit_parse(const char *str) exit(1); } - enable_mlock = qemu_opt_get_bool(opts, "mem-lock", - should_mlock(mlock_state)); - mlock_state = enable_mlock ? MLOCK_ON : MLOCK_OFF; - 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) { + return; + } + + if (strcmp(mem_lock_opt, "on") == 0) { + mlock_state = MLOCK_ON; + return; + } + + if (strcmp(mem_lock_opt, "off") == 0) { + mlock_state = MLOCK_OFF; + return; + } + + if (strcmp(mem_lock_opt, "on-fault") == 0) { + mlock_state = MLOCK_ON_FAULT; + return; + } + + error_report("parameter 'mem-lock' expects one of " + "'on', 'off', 'on-fault'"); + exit(1); } /* -- cgit 1.4.1