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[91.12.111.174]) by smtp.gmail.com with ESMTPSA id e10sm15831460wrw.20.2021.05.04.04.08.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 May 2021 04:08:03 -0700 (PDT) Subject: Re: [PATCH v7 10/15] hostmem: Wire up RAM_NORESERVE via "reserve" property To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20210428133754.10713-1-david@redhat.com> <20210428133754.10713-11-david@redhat.com> From: David Hildenbrand Organization: Red Hat Message-ID: <1a865f85-f616-993f-58e1-bb441cec344b@redhat.com> Date: Tue, 4 May 2021 13:08:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.697, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-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: , Cc: Marcel Apfelbaum , Eduardo Habkost , "Michael S. Tsirkin" , Richard Henderson , Markus Armbruster , Peter Xu , qemu-devel@nongnu.org, Greg Kurz , Paolo Bonzini , Stefan Hajnoczi , Murilo Opsfelder Araujo , Igor Mammedov , Nitesh Lal , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 04.05.21 12:12, Daniel P. Berrangé wrote: > On Wed, Apr 28, 2021 at 03:37:49PM +0200, David Hildenbrand wrote: >> Let's provide a way to control the use of RAM_NORESERVE via memory >> backends using the "reserve" property which defaults to true (old >> behavior). >> >> Only Linux currently supports clearing the flag (and support is checked at >> runtime, depending on the setting of "/proc/sys/vm/overcommit_memory"). >> Windows and other POSIX systems will bail out with "reserve=false". >> >> The target use case is virtio-mem, which dynamically exposes memory >> inside a large, sparse memory area to the VM. This essentially allows >> avoiding to set "/proc/sys/vm/overcommit_memory == 0") when using >> virtio-mem and also supporting hugetlbfs in the future. >> >> Reviewed-by: Peter Xu >> Reviewed-by: Eduardo Habkost >> Reviewed-by: Markus Armbruster >> Acked-by: Eduardo Habkost for memory backend and machine core >> Cc: Markus Armbruster >> Cc: Eric Blake >> Cc: Igor Mammedov >> Signed-off-by: David Hildenbrand >> --- >> backends/hostmem-file.c | 11 ++++++----- >> backends/hostmem-memfd.c | 1 + >> backends/hostmem-ram.c | 1 + >> backends/hostmem.c | 32 ++++++++++++++++++++++++++++++++ >> include/sysemu/hostmem.h | 2 +- >> qapi/qom.json | 10 ++++++++++ >> 6 files changed, 51 insertions(+), 6 deletions(-) >> >> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c >> index b683da9daf..9d550e53d4 100644 >> --- a/backends/hostmem-file.c >> +++ b/backends/hostmem-file.c >> @@ -40,6 +40,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) >> object_get_typename(OBJECT(backend))); >> #else >> HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(backend); >> + uint32_t ram_flags; >> gchar *name; >> >> if (!backend->size) { >> @@ -52,11 +53,11 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) >> } >> >> name = host_memory_backend_get_name(backend); >> - memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), >> - name, >> - backend->size, fb->align, >> - (backend->share ? RAM_SHARED : 0) | >> - (fb->is_pmem ? RAM_PMEM : 0), >> + ram_flags = backend->share ? RAM_SHARED : 0; >> + ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; >> + ram_flags |= fb->is_pmem ? RAM_PMEM : 0; >> + memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name, >> + backend->size, fb->align, ram_flags, >> fb->mem_path, fb->readonly, errp); >> g_free(name); >> #endif >> diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c >> index 93b5d1a4cf..f3436b623d 100644 >> --- a/backends/hostmem-memfd.c >> +++ b/backends/hostmem-memfd.c >> @@ -55,6 +55,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) >> >> name = host_memory_backend_get_name(backend); >> ram_flags = backend->share ? RAM_SHARED : 0; >> + ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; >> memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name, >> backend->size, ram_flags, fd, 0, errp); >> g_free(name); >> diff --git a/backends/hostmem-ram.c b/backends/hostmem-ram.c >> index 741e701062..b8e55cdbd0 100644 >> --- a/backends/hostmem-ram.c >> +++ b/backends/hostmem-ram.c >> @@ -29,6 +29,7 @@ ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) >> >> name = host_memory_backend_get_name(backend); >> ram_flags = backend->share ? RAM_SHARED : 0; >> + ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; >> memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend), name, >> backend->size, ram_flags, errp); >> g_free(name); >> diff --git a/backends/hostmem.c b/backends/hostmem.c >> index c6c1ff5b99..58fdc1b658 100644 >> --- a/backends/hostmem.c >> +++ b/backends/hostmem.c >> @@ -217,6 +217,11 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value, >> Error *local_err = NULL; >> HostMemoryBackend *backend = MEMORY_BACKEND(obj); >> >> + if (!backend->reserve && value) { >> + error_setg(errp, "'prealloc=on' and 'reserve=off' are incompatible"); >> + return; >> + } >> + >> if (!host_memory_backend_mr_inited(backend)) { >> backend->prealloc = value; >> return; >> @@ -268,6 +273,7 @@ static void host_memory_backend_init(Object *obj) >> /* TODO: convert access to globals to compat properties */ >> backend->merge = machine_mem_merge(machine); >> backend->dump = machine_dump_guest_core(machine); >> + backend->reserve = true; >> backend->prealloc_threads = 1; >> } >> >> @@ -426,6 +432,28 @@ static void host_memory_backend_set_share(Object *o, bool value, Error **errp) >> backend->share = value; >> } >> >> +static bool host_memory_backend_get_reserve(Object *o, Error **errp) >> +{ >> + HostMemoryBackend *backend = MEMORY_BACKEND(o); >> + >> + return backend->reserve; >> +} >> + >> +static void host_memory_backend_set_reserve(Object *o, bool value, Error **errp) >> +{ >> + HostMemoryBackend *backend = MEMORY_BACKEND(o); >> + >> + if (host_memory_backend_mr_inited(backend)) { >> + error_setg(errp, "cannot change property value"); >> + return; >> + } >> + if (backend->prealloc && !value) { >> + error_setg(errp, "'prealloc=on' and 'reserve=off' are incompatible"); >> + return; >> + } >> + backend->reserve = value; >> +} >> + >> static bool >> host_memory_backend_get_use_canonical_path(Object *obj, Error **errp) >> { >> @@ -494,6 +522,10 @@ host_memory_backend_class_init(ObjectClass *oc, void *data) >> host_memory_backend_get_share, host_memory_backend_set_share); >> object_class_property_set_description(oc, "share", >> "Mark the memory as private to QEMU or shared"); >> + object_class_property_add_bool(oc, "reserve", >> + host_memory_backend_get_reserve, host_memory_backend_set_reserve); >> + object_class_property_set_description(oc, "reserve", >> + "Reserve swap space (or huge pages) if applicable"); >> /* >> * Do not delete/rename option. This option must be considered stable >> * (as if it didn't have the 'x-' prefix including deprecation period) as >> diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h >> index df5644723a..9ff5c16963 100644 >> --- a/include/sysemu/hostmem.h >> +++ b/include/sysemu/hostmem.h >> @@ -64,7 +64,7 @@ struct HostMemoryBackend { >> /* protected */ >> uint64_t size; >> bool merge, dump, use_canonical_path; >> - bool prealloc, is_mapped, share; >> + bool prealloc, is_mapped, share, reserve; >> uint32_t prealloc_threads; >> DECLARE_BITMAP(host_nodes, MAX_NODES + 1); >> HostMemPolicy policy; >> diff --git a/qapi/qom.json b/qapi/qom.json >> index cd0e76d564..4fa3137aab 100644 >> --- a/qapi/qom.json >> +++ b/qapi/qom.json >> @@ -545,6 +545,9 @@ >> # @share: if false, the memory is private to QEMU; if true, it is shared >> # (default: false) >> # >> +# @reserve: if true, reserve swap space (or huge pages) if applicable >> +# default: true) >> +# >> # @size: size of the memory region in bytes >> # >> # @x-use-canonical-path-for-ramblock-id: if true, the canoncial path is used >> @@ -556,6 +559,12 @@ >> # false generally, but true for machine >> # types <= 4.0) >> # >> +# Note: prealloc=true and reserve=false cannot be set at the same time. With >> +# reserve=true, the behavior depends on the operating system: for example, >> +# Linux will not reserve swap space for shared file mappings -- >> +# "not applicable". In contrast, reserve=false will bail out if it cannot >> +# be configured accordingly. >> +# >> # Since: 2.1 >> ## >> { 'struct': 'MemoryBackendProperties', >> @@ -566,6 +575,7 @@ >> '*prealloc': 'bool', >> '*prealloc-threads': 'uint32', >> '*share': 'bool', >> + '*reserve': 'bool', >> 'size': 'size', >> '*x-use-canonical-path-for-ramblock-id': 'bool' } } > > IIUC from the previous patch in the series, 'reserve' is only implemented > on Linux. If we make this QAPI prop dependant on CONFIG_LINUX, then mgmt > apps will do the right thing to detect what platform(s) it works on. Would that mean only conditionally calling (or ifdeffing) the object_property_add_* in backends/hostmem.c? Note that the "share" property is basically ignored on Windows and only implemented on POSIX and we don't even bail out when set ... Thanks! -- Thanks, David / dhildenb