On Thu, 10 Mar 2022 10:36:08 -0500 Steven Sistare <steven.sist...@oracle.com> wrote:
> On 3/8/2022 2:20 AM, Igor Mammedov wrote: > > On Tue, 8 Mar 2022 01:50:11 -0500 > > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > >> On Mon, Mar 07, 2022 at 09:41:44AM -0500, Steven Sistare wrote: > >>> On 3/4/2022 5:41 AM, Igor Mammedov wrote: > >>>> On Thu, 3 Mar 2022 12:21:15 -0500 > >>>> "Michael S. Tsirkin" <m...@redhat.com> wrote: > >>>> > >>>>> On Wed, Dec 22, 2021 at 11:05:15AM -0800, Steve Sistare wrote: > >>>>>> Allocate anonymous memory using memfd_create if the memfd-alloc machine > >>>>>> option is set. > >>>>>> > >>>>>> Signed-off-by: Steve Sistare <steven.sist...@oracle.com> > >>>>>> --- > >>>>>> hw/core/machine.c | 19 +++++++++++++++++++ > >>>>>> include/hw/boards.h | 1 + > >>>>>> qemu-options.hx | 6 ++++++ > >>>>>> softmmu/physmem.c | 47 > >>>>>> ++++++++++++++++++++++++++++++++++++++--------- > >>>>>> softmmu/vl.c | 1 + > >>>>>> trace-events | 1 + > >>>>>> util/qemu-config.c | 4 ++++ > >>>>>> 7 files changed, 70 insertions(+), 9 deletions(-) > >>>>>> > >>>>>> diff --git a/hw/core/machine.c b/hw/core/machine.c > >>>>>> index 53a99ab..7739d88 100644 > >>>>>> --- a/hw/core/machine.c > >>>>>> +++ b/hw/core/machine.c > >>>>>> @@ -392,6 +392,20 @@ static void machine_set_mem_merge(Object *obj, > >>>>>> bool value, Error **errp) > >>>>>> ms->mem_merge = value; > >>>>>> } > >>>>>> > >>>>>> +static bool machine_get_memfd_alloc(Object *obj, Error **errp) > >>>>>> +{ > >>>>>> + MachineState *ms = MACHINE(obj); > >>>>>> + > >>>>>> + return ms->memfd_alloc; > >>>>>> +} > >>>>>> + > >>>>>> +static void machine_set_memfd_alloc(Object *obj, bool value, Error > >>>>>> **errp) > >>>>>> +{ > >>>>>> + MachineState *ms = MACHINE(obj); > >>>>>> + > >>>>>> + ms->memfd_alloc = value; > >>>>>> +} > >>>>>> + > >>>>>> static bool machine_get_usb(Object *obj, Error **errp) > >>>>>> { > >>>>>> MachineState *ms = MACHINE(obj); > >>>>>> @@ -829,6 +843,11 @@ static void machine_class_init(ObjectClass *oc, > >>>>>> void *data) > >>>>>> object_class_property_set_description(oc, "mem-merge", > >>>>>> "Enable/disable memory merge support"); > >>>>>> > >>>>>> + object_class_property_add_bool(oc, "memfd-alloc", > >>>>>> + machine_get_memfd_alloc, machine_set_memfd_alloc); > >>>>>> + object_class_property_set_description(oc, "memfd-alloc", > >>>>>> + "Enable/disable allocating anonymous memory using > >>>>>> memfd_create"); > >>>>>> + > >>>>>> object_class_property_add_bool(oc, "usb", > >>>>>> machine_get_usb, machine_set_usb); > >>>>>> object_class_property_set_description(oc, "usb", > >>>>>> diff --git a/include/hw/boards.h b/include/hw/boards.h > >>>>>> index 9c1c190..a57d7a0 100644 > >>>>>> --- a/include/hw/boards.h > >>>>>> +++ b/include/hw/boards.h > >>>>>> @@ -327,6 +327,7 @@ struct MachineState { > >>>>>> char *dt_compatible; > >>>>>> bool dump_guest_core; > >>>>>> bool mem_merge; > >>>>>> + bool memfd_alloc; > >>>>>> bool usb; > >>>>>> bool usb_disabled; > >>>>>> char *firmware; > >>>>>> diff --git a/qemu-options.hx b/qemu-options.hx > >>>>>> index 7d47510..33c8173 100644 > >>>>>> --- a/qemu-options.hx > >>>>>> +++ b/qemu-options.hx > >>>>>> @@ -30,6 +30,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ > >>>>>> " vmport=on|off|auto controls emulation of vmport > >>>>>> (default: auto)\n" > >>>>>> " dump-guest-core=on|off include guest memory in a > >>>>>> core dump (default=on)\n" > >>>>>> " mem-merge=on|off controls memory merge support > >>>>>> (default: on)\n" > >>>>>> + " memfd-alloc=on|off controls allocating anonymous > >>>>>> guest RAM using memfd_create (default: off)\n" > >>>>> > >>>>> Question: are there any disadvantages associated with using > >>>>> memfd_create? I guess we are using up an fd, but that seems minor. Any > >>>>> reason not to set to on by default? maybe with a fallback option to > >>>>> disable that? > >>> > >>> Old Linux host kernels, circa 4.1, do not support huge pages for shared > >>> memory. > >>> Also, the tunable to enable huge pages for share memory is different than > >>> for > >>> anon memory, so there could be performance loss if it is not set > >>> correctly. > >>> /sys/kernel/mm/transparent_hugepage/enabled > >>> vs > >>> /sys/kernel/mm/transparent_hugepage/shmem_enabled > >> > >> I guess we can test this when launching the VM, and select > >> a good default. > >> > >>> It might make sense to use memfd_create by default for the secondary > >>> segments. > >> > >> Well there's also KSM now you mention it. > > > > then another quest, is there downside to always using memfd_create > > without any knobs being involved? > > Lower performance if small pages are used (but Michael suggests qemu could > automatically check the tunable and use anon memory instead) > > KSM (same page merging) is not supported for shared memory, so ram_block_add > -> > memory_try_enable_merging will not enable it. > > In both cases, I expect the degradation would be negligible if memfd_create is > only automatically applied to the secondary segments, which are typically > small. > But, someone's secondary segment could be larger, and it is time consuming to > prove innocence when someone claims your change caused their performance > regression. Adding David as memory subsystem maintainer, maybe he will a better idea instead of introducing global knob that would also magically alter backends' behavior despite of its their configured settings. > - Steve > > >>>>> I am concerned that it's actually a kind of memory backend, this flag > >>>>> seems to instead be closer to the deprecated mem-prealloc. E.g. > >>>>> it does not work with a mem path, does it? > >>> > >>> One can still define a memory backend with mempath to create the main ram > >>> segment, > >>> though it must be some form of shared to work with live update. Indeed, > >>> I would > >>> expect most users to specify an explicit memory backend for it. The > >>> secondary > >>> segments would still use memfd_create. > >>> > >>>> (mem path and mem-prealloc are transparently aliased to used memory > >>>> backend > >>>> if I recall it right.) > >>>> > >>>> Steve, > >>>> > >>>> For allocating guest RAM, we switched exclusively to using > >>>> memory-backends > >>>> including initial guest RAM (-m size option) and we have hostmem-memfd > >>>> that uses memfd_create() and I'd rather avoid adding random knobs to > >>>> machine > >>>> for tweaking how RAM should be allocated, we have memory backends for > >>>> this, > >>>> so this patch begs the question: why hostmem-memfd is not sufficient? > >>>> (patch description is rather lacking on rationale behind the patch) > >>> > >>> There is currently no way to specify memory backends for the secondary > >>> memory > >>> segments (vram, roms, etc), and IMO it would be onerous to specify a > >>> backend for > >>> each of them. On x86_64, these include pc.bios, vga.vram, pc.rom, > >>> vga.rom, > >>> /rom@etc/acpi/tables, /rom@etc/table-loader, /rom@etc/acpi/rsdp. MemoryRegion is not the only place where state is stored. If we only talk about fwcfg entries state, it can also reference plain malloced memory allocated elsewhere or make a deep copy internally. Similarly devices also may store state outside of RamBlock framework. How are you dealing with that? > >>> > >>> - Steve > >>> > >>>>>> " aes-key-wrap=on|off controls support for AES key > >>>>>> wrapping (default=on)\n" > >>>>>> " dea-key-wrap=on|off controls support for DEA key > >>>>>> wrapping (default=on)\n" > >>>>>> " suppress-vmdesc=on|off disables self-describing > >>>>>> migration (default=off)\n" > >>>>>> @@ -76,6 +77,11 @@ SRST > >>>>>> supported by the host, de-duplicates identical memory pages > >>>>>> among VMs instances (enabled by default). > >>>>>> > >>>>>> + ``memfd-alloc=on|off`` > >>>>>> + Enables or disables allocation of anonymous guest RAM using > >>>>>> + memfd_create. Any associated memory-backend objects are > >>>>>> created with > >>>>>> + share=on. The memfd-alloc default is off. > >>>>>> + > >>>>>> ``aes-key-wrap=on|off`` > >>>>>> Enables or disables AES key wrapping support on s390-ccw > >>>>>> hosts. > >>>>>> This feature controls whether AES wrapping keys will be > >>>>>> created > >>>>>> diff --git a/softmmu/physmem.c b/softmmu/physmem.c > >>>>>> index 3524c04..95e2b49 100644 > >>>>>> --- a/softmmu/physmem.c > >>>>>> +++ b/softmmu/physmem.c > >>>>>> @@ -41,6 +41,7 @@ > >>>>>> #include "qemu/config-file.h" > >>>>>> #include "qemu/error-report.h" > >>>>>> #include "qemu/qemu-print.h" > >>>>>> +#include "qemu/memfd.h" > >>>>>> #include "exec/memory.h" > >>>>>> #include "exec/ioport.h" > >>>>>> #include "sysemu/dma.h" > >>>>>> @@ -1964,35 +1965,63 @@ static void ram_block_add(RAMBlock *new_block, > >>>>>> Error **errp) > >>>>>> const bool shared = qemu_ram_is_shared(new_block); > >>>>>> RAMBlock *block; > >>>>>> RAMBlock *last_block = NULL; > >>>>>> + struct MemoryRegion *mr = new_block->mr; > >>>>>> ram_addr_t old_ram_size, new_ram_size; > >>>>>> Error *err = NULL; > >>>>>> + const char *name; > >>>>>> + void *addr = 0; > >>>>>> + size_t maxlen; > >>>>>> + MachineState *ms = MACHINE(qdev_get_machine()); > >>>>>> > >>>>>> old_ram_size = last_ram_page(); > >>>>>> > >>>>>> qemu_mutex_lock_ramlist(); > >>>>>> - new_block->offset = find_ram_offset(new_block->max_length); > >>>>>> + maxlen = new_block->max_length; > >>>>>> + new_block->offset = find_ram_offset(maxlen); > >>>>>> > >>>>>> if (!new_block->host) { > >>>>>> if (xen_enabled()) { > >>>>>> - xen_ram_alloc(new_block->offset, new_block->max_length, > >>>>>> - new_block->mr, &err); > >>>>>> + xen_ram_alloc(new_block->offset, maxlen, new_block->mr, > >>>>>> &err); > >>>>>> if (err) { > >>>>>> error_propagate(errp, err); > >>>>>> qemu_mutex_unlock_ramlist(); > >>>>>> return; > >>>>>> } > >>>>>> } else { > >>>>>> - new_block->host = > >>>>>> qemu_anon_ram_alloc(new_block->max_length, > >>>>>> - > >>>>>> &new_block->mr->align, > >>>>>> - shared, noreserve); > >>>>>> - if (!new_block->host) { > >>>>>> + name = memory_region_name(mr); > >>>>>> + if (ms->memfd_alloc) { > >>>>>> + Object *parent = &mr->parent_obj; > >>>>>> + int mfd = -1; /* placeholder until next > >>>>>> patch */ > >>>>>> + mr->align = QEMU_VMALLOC_ALIGN; > >>>>>> + if (mfd < 0) { > >>>>>> + mfd = qemu_memfd_create(name, maxlen + mr->align, > >>>>>> + 0, 0, 0, &err); > >>>>>> + if (mfd < 0) { > >>>>>> + return; > >>>>>> + } > >>>>>> + } > >>>>>> + qemu_set_cloexec(mfd); > >>>>>> + /* The memory backend already set its desired flags. > >>>>>> */ > >>>>>> + if (!object_dynamic_cast(parent, > >>>>>> TYPE_MEMORY_BACKEND)) { > >>>>>> + new_block->flags |= RAM_SHARED; > >>>>>> + } > >>>>>> + addr = file_ram_alloc(new_block, maxlen, mfd, > >>>>>> + false, false, 0, errp); > >>>>>> + trace_anon_memfd_alloc(name, maxlen, addr, mfd); > >>>>>> + } else { > >>>>>> + addr = qemu_anon_ram_alloc(maxlen, &mr->align, > >>>>>> + shared, noreserve); > >>>>>> + } > >>>>>> + > >>>>>> + if (!addr) { > >>>>>> error_setg_errno(errp, errno, > >>>>>> "cannot set up guest memory '%s'", > >>>>>> - memory_region_name(new_block->mr)); > >>>>>> + name); > >>>>>> qemu_mutex_unlock_ramlist(); > >>>>>> return; > >>>>>> } > >>>>>> - memory_try_enable_merging(new_block->host, > >>>>>> new_block->max_length); > >>>>>> + memory_try_enable_merging(addr, maxlen); > >>>>>> + new_block->host = addr; > >>>>>> } > >>>>>> } > >>>>>> > >>>>>> diff --git a/softmmu/vl.c b/softmmu/vl.c > >>>>>> index 620a1f1..ab3648a 100644 > >>>>>> --- a/softmmu/vl.c > >>>>>> +++ b/softmmu/vl.c > >>>>>> @@ -2440,6 +2440,7 @@ static void create_default_memdev(MachineState > >>>>>> *ms, const char *path) > >>>>>> object_property_set_str(obj, "mem-path", path, &error_fatal); > >>>>>> } > >>>>>> object_property_set_int(obj, "size", ms->ram_size, &error_fatal); > >>>>>> + object_property_set_bool(obj, "share", ms->memfd_alloc, > >>>>>> &error_fatal); > >>>>>> object_property_add_child(object_get_objects_root(), > >>>>>> mc->default_ram_id, > >>>>>> obj); > >>>>>> /* Ensure backend's memory region name is equal to > >>>>>> mc->default_ram_id */ > >>>>>> diff --git a/trace-events b/trace-events > >>>>>> index a637a61..770a9ac 100644 > >>>>>> --- a/trace-events > >>>>>> +++ b/trace-events > >>>>>> @@ -45,6 +45,7 @@ ram_block_discard_range(const char *rbname, void > >>>>>> *hva, size_t length, bool need_ > >>>>>> # accel/tcg/cputlb.c > >>>>>> memory_notdirty_write_access(uint64_t vaddr, uint64_t ram_addr, > >>>>>> unsigned size) "0x%" PRIx64 " ram_addr 0x%" PRIx64 " size %u" > >>>>>> memory_notdirty_set_dirty(uint64_t vaddr) "0x%" PRIx64 > >>>>>> +anon_memfd_alloc(const char *name, size_t size, void *ptr, int fd) > >>>>>> "%s size %zu ptr %p fd %d" > >>>>>> > >>>>>> # gdbstub.c > >>>>>> gdbstub_op_start(const char *device) "Starting gdbstub using device > >>>>>> %s" > >>>>>> diff --git a/util/qemu-config.c b/util/qemu-config.c > >>>>>> index 436ab63..3606e5c 100644 > >>>>>> --- a/util/qemu-config.c > >>>>>> +++ b/util/qemu-config.c > >>>>>> @@ -207,6 +207,10 @@ static QemuOptsList machine_opts = { > >>>>>> .type = QEMU_OPT_BOOL, > >>>>>> .help = "enable/disable memory merge support", > >>>>>> },{ > >>>>>> + .name = "memfd-alloc", > >>>>>> + .type = QEMU_OPT_BOOL, > >>>>>> + .help = "enable/disable memfd_create for anonymous > >>>>>> memory", > >>>>>> + },{ > >>>>>> .name = "usb", > >>>>>> .type = QEMU_OPT_BOOL, > >>>>>> .help = "Set on/off to enable/disable usb", > >>>>>> -- > >>>>>> 1.8.3.1 > >>>>> > >>>>> > >>>> > >> > > >