On 3/10/2022 11:00 AM, Igor Mammedov wrote: > 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.
OK, in ram_block_add I can set the RAM_SHARED flag based on the memory-backend object's shared flag. I already set the latter in create_default_memdev when memfd-alloc is specified. With that change, we do not override configured settings. Users can no longer use memory-backend-ram for CPR, and must change all memory-backend-ram to memory-backend-memfd in the command-line arguments. That is fine. With that change, are you OK with this patch? - 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 >>>>>>> >>>>>>> >>>>>> >>>> >>> >> >