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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/28 03:47:08 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -36 X-Spam_score: -3.7 X-Spam_bar: --- X-Spam_report: (-3.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.576, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.011, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=-1, RCVD_IN_MSPIKE_WL=-0.01, 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: Igor Mammedov , Wei Yang , Qemu Developers , "Dr . David Alan Gilbert" , "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 25.09.20 15:46, Pankaj Gupta wrote: >> Let's allow a minimum block size of 1 MiB in all configurations. Use >> a default block size based on the THP size, and warn if something >> smaller is configured by the user. >> >> VIRTIO_MEM only supports Linux (depends on LINUX), so we can probe the >> THP size unconditionally. >> >> For now we only support virtio-mem on x86-64 - there isn't a user-visiable >> change (x86-64 only supports 2 MiB THP on the PMD level) - the default >> was, and will be 2 MiB. >> >> If we ever have THP on the PUD level (e.g., 1 GiB THP on x86-64), we >> expect to have a trigger to explicitly opt-in for the new THP granularity. >> >> Cc: "Michael S. Tsirkin" >> Cc: Wei Yang >> Cc: Dr. David Alan Gilbert >> Cc: Igor Mammedov >> Cc: Pankaj Gupta >> Signed-off-by: David Hildenbrand >> --- >> hw/virtio/virtio-mem.c | 82 +++++++++++++++++++++++++++++++++++++++--- >> 1 file changed, 78 insertions(+), 4 deletions(-) >> >> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c >> index 8fbec77ccc..58098686ee 100644 >> --- a/hw/virtio/virtio-mem.c >> +++ b/hw/virtio/virtio-mem.c >> @@ -33,10 +33,70 @@ >> #include "trace.h" >> >> /* >> - * Use QEMU_VMALLOC_ALIGN, so no THP will have to be split when unplugging >> - * memory (e.g., 2MB on x86_64). >> + * Let's not allow blocks smaller than 1 MiB, for example, to keep the tracking >> + * bitmap small. >> */ >> -#define VIRTIO_MEM_MIN_BLOCK_SIZE ((uint32_t)QEMU_VMALLOC_ALIGN) >> +#define VIRTIO_MEM_MIN_BLOCK_SIZE ((uint32_t)(1 * MiB)) >> + >> +/* >> + * We want to have a reasonable default block size such that >> + * 1. We avoid splitting THPs when unplugging memory, which degrades >> + * performance. >> + * 2. We avoid placing THPs for plugged blocks that also cover unplugged >> + * blocks. >> + * >> + * The actual THP size might differ between Linux kernels, so we try to probe >> + * it. In the future (if we ever run into issues regarding 2.), we might want >> + * to disable THP in case we fail to properly probe the THP size, or if the >> + * block size is configured smaller than the THP size. >> + */ >> +static uint32_t default_block_size; >> + >> +#define HPAGE_PMD_SIZE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size" >> +static uint32_t virtio_mem_default_block_size(void) >> +{ >> + gchar *content = NULL; >> + const char *endptr; >> + uint64_t tmp; >> + >> + if (default_block_size) { >> + return default_block_size; >> + } >> + >> + /* >> + * Try to probe the actual THP size, fallback to (sane but eventually >> + * incorrect) default sizes. >> + */ >> + if (g_file_get_contents(HPAGE_PMD_SIZE_PATH, &content, NULL, NULL) && >> + !qemu_strtou64(content, &endptr, 0, &tmp) && >> + (!endptr || *endptr == '\n')) { >> + /* >> + * Sanity-check the value, if it's too big (e.g., aarch64 with 64k base >> + * pages) or weird, fallback to something smaller. >> + */ >> + if (!tmp || !is_power_of_2(tmp) || tmp > 16 * MiB) { >> + warn_report("Detected a THP size of %" PRIx64 >> + " MiB, falling back to 1 MiB.", tmp / MiB); >> + default_block_size = 1 * MiB; > > Probably use macro "VIRTIO_MEM_MIN_BLOCK_SIZE" Indeed. >> + } else { >> + default_block_size = tmp; >> + } >> + } else { >> +#if defined(__x86_64__) || defined(__arm__) || defined(__aarch64__) || \ >> + defined(__powerpc64__) >> + default_block_size = 2 * MiB; >> +#else >> + /* fallback to 1 MiB (e.g., the THP size on s390x) */ >> + default_block_size = 1 * MiB; >> +#endif > > Maybe we can declare this macro near to "VIRTIO_MEM_MIN_BLOCK_SIZE > ((uint32_t)(1 * MiB))" > or club into one, just a thought. I decided to not use VIRTIO_MEM_MIN_BLOCK_SIZE here to not accidentally mess up the s390x THP size when ever wanting to decrease VIRTIO_MEM_MIN_BLOCK_SIZE. But as we have a comment here, people should know whats happening when ever changing VIRTIO_MEM_MIN_BLOCK_SIZE. Thanks! -- Thanks, David / dhildenb