From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3693AC433EF for ; Fri, 17 Dec 2021 13:54:44 +0000 (UTC) Received: from localhost ([::1]:51254 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1myDh5-0006ff-7b for qemu-devel@archiver.kernel.org; Fri, 17 Dec 2021 08:54:43 -0500 Received: from eggs.gnu.org ([209.51.188.92]:54010) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1myDZ8-0005YO-Is for qemu-devel@nongnu.org; Fri, 17 Dec 2021 08:46:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:37557) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1myDZ5-0008EZ-Ut for qemu-devel@nongnu.org; Fri, 17 Dec 2021 08:46:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639748787; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nRAI2HEPBW7S+0GYkiI9WAhdb4aMzzmsMdVOd8bcCsc=; b=d7QN4u6wX695LzG1vVVlJxqS+enyfUvh6Pv/8WSBjMqJ8AUY2kagjTscVipMxMmgCQ7aWI opJgaKH0wb8ZUe6CZijuWti6AdlU1DSt8x+gLsbGSLPYcrUhK+H8UIC0N0M6zqEIXql6py XIWiADA3jCCXliHv3oT3Vojix5pFJ/E= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-554-QEqTgWQkPLCymDdGp1sLiw-1; Fri, 17 Dec 2021 08:46:22 -0500 X-MC-Unique: QEqTgWQkPLCymDdGp1sLiw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BAEC81015DA0; Fri, 17 Dec 2021 13:46:21 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.193.204]) by smtp.corp.redhat.com (Postfix) with ESMTP id EB6375E482; Fri, 17 Dec 2021 13:46:18 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v2 2/8] util/oslib-posix: Support MADV_POPULATE_WRITE for os_mem_prealloc() Date: Fri, 17 Dec 2021 14:46:05 +0100 Message-Id: <20211217134611.31172-3-david@redhat.com> In-Reply-To: <20211217134611.31172-1-david@redhat.com> References: <20211217134611.31172-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; 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=-0.718, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Pankaj Gupta , Gavin Shan , =?UTF-8?q?Daniel=20P=20=2E=20Berrang=C3=A9?= , Eduardo Habkost , "Michael S. Tsirkin" , =?UTF-8?q?Michal=20Pr=C3=ADvozn=C3=ADk?= , David Hildenbrand , "Dr . David Alan Gilbert" , Pankaj Gupta , Sebastien Boeuf , Igor Mammedov , Paolo Bonzini , Hui Zhu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Let's sense support and use it for preallocation. MADV_POPULATE_WRITE does not require a SIGBUS handler, doesn't actually touch page content, and avoids context switches; it is, therefore, faster and easier to handle than our current approach. While MADV_POPULATE_WRITE is, in general, faster than manual prefaulting, and especially faster with 4k pages, there is still value in prefaulting using multiple threads to speed up preallocation. More details on MADV_POPULATE_WRITE can be found in the Linux commits 4ca9b3859dac ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables") and eb2faa513c24 ("mm/madvise: report SIGBUS as -EFAULT for MADV_POPULATE_(READ|WRITE)"), and in the man page proposal [1]. This resolves the TODO in do_touch_pages(). In the future, we might want to look into using fallocate(), eventually combined with MADV_POPULATE_READ, when dealing with shared file/fd mappings and not caring about memory bindings. [1] https://lkml.kernel.org/r/20210816081922.5155-1-david@redhat.com Reviewed-by: Pankaj Gupta Reviewed-by: Daniel P. Berrangé Reviewed-by: Michal Privoznik Signed-off-by: David Hildenbrand --- include/qemu/osdep.h | 7 ++++ util/oslib-posix.c | 83 +++++++++++++++++++++++++++++++++----------- 2 files changed, 69 insertions(+), 21 deletions(-) diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index 60718fc342..d1660d67fa 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -471,6 +471,11 @@ static inline void qemu_cleanup_generic_vfree(void *p) #else #define QEMU_MADV_REMOVE QEMU_MADV_DONTNEED #endif +#ifdef MADV_POPULATE_WRITE +#define QEMU_MADV_POPULATE_WRITE MADV_POPULATE_WRITE +#else +#define QEMU_MADV_POPULATE_WRITE QEMU_MADV_INVALID +#endif #elif defined(CONFIG_POSIX_MADVISE) @@ -484,6 +489,7 @@ static inline void qemu_cleanup_generic_vfree(void *p) #define QEMU_MADV_HUGEPAGE QEMU_MADV_INVALID #define QEMU_MADV_NOHUGEPAGE QEMU_MADV_INVALID #define QEMU_MADV_REMOVE QEMU_MADV_DONTNEED +#define QEMU_MADV_POPULATE_WRITE QEMU_MADV_INVALID #else /* no-op */ @@ -497,6 +503,7 @@ static inline void qemu_cleanup_generic_vfree(void *p) #define QEMU_MADV_HUGEPAGE QEMU_MADV_INVALID #define QEMU_MADV_NOHUGEPAGE QEMU_MADV_INVALID #define QEMU_MADV_REMOVE QEMU_MADV_INVALID +#define QEMU_MADV_POPULATE_WRITE QEMU_MADV_INVALID #endif diff --git a/util/oslib-posix.c b/util/oslib-posix.c index b146beef78..cb89e07770 100644 --- a/util/oslib-posix.c +++ b/util/oslib-posix.c @@ -484,10 +484,6 @@ static void *do_touch_pages(void *arg) * * 'volatile' to stop compiler optimizing this away * to a no-op - * - * TODO: get a better solution from kernel so we - * don't need to write at all so we don't cause - * wear on the storage backing the region... */ *(volatile char *)addr = *addr; addr += hpagesize; @@ -497,6 +493,26 @@ static void *do_touch_pages(void *arg) return (void *)(uintptr_t)ret; } +static void *do_madv_populate_write_pages(void *arg) +{ + MemsetThread *memset_args = (MemsetThread *)arg; + const size_t size = memset_args->numpages * memset_args->hpagesize; + char * const addr = memset_args->addr; + int ret = 0; + + /* See do_touch_pages(). */ + qemu_mutex_lock(&page_mutex); + while (!threads_created_flag) { + qemu_cond_wait(&page_cond, &page_mutex); + } + qemu_mutex_unlock(&page_mutex); + + if (size && qemu_madvise(addr, size, QEMU_MADV_POPULATE_WRITE)) { + ret = -errno; + } + return (void *)(uintptr_t)ret; +} + static inline int get_memset_num_threads(int smp_cpus) { long host_procs = sysconf(_SC_NPROCESSORS_ONLN); @@ -510,10 +526,11 @@ static inline int get_memset_num_threads(int smp_cpus) } static int touch_all_pages(char *area, size_t hpagesize, size_t numpages, - int smp_cpus) + int smp_cpus, bool use_madv_populate_write) { static gsize initialized = 0; size_t numpages_per_thread, leftover; + void *(*touch_fn)(void *); int ret = 0, i = 0; char *addr = area; @@ -523,6 +540,12 @@ static int touch_all_pages(char *area, size_t hpagesize, size_t numpages, g_once_init_leave(&initialized, 1); } + if (use_madv_populate_write) { + touch_fn = do_madv_populate_write_pages; + } else { + touch_fn = do_touch_pages; + } + threads_created_flag = false; memset_num_threads = get_memset_num_threads(smp_cpus); memset_thread = g_new0(MemsetThread, memset_num_threads); @@ -533,7 +556,7 @@ static int touch_all_pages(char *area, size_t hpagesize, size_t numpages, memset_thread[i].numpages = numpages_per_thread + (i < leftover); memset_thread[i].hpagesize = hpagesize; qemu_thread_create(&memset_thread[i].pgthread, "touch_pages", - do_touch_pages, &memset_thread[i], + touch_fn, &memset_thread[i], QEMU_THREAD_JOINABLE); addr += memset_thread[i].numpages * hpagesize; } @@ -556,6 +579,12 @@ static int touch_all_pages(char *area, size_t hpagesize, size_t numpages, return ret; } +static bool madv_populate_write_possible(char *area, size_t pagesize) +{ + return !qemu_madvise(area, pagesize, QEMU_MADV_POPULATE_WRITE) || + errno != EINVAL; +} + void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus, Error **errp) { @@ -563,30 +592,42 @@ void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus, struct sigaction act, oldact; size_t hpagesize = qemu_fd_getpagesize(fd); size_t numpages = DIV_ROUND_UP(memory, hpagesize); + bool use_madv_populate_write; - memset(&act, 0, sizeof(act)); - act.sa_handler = &sigbus_handler; - act.sa_flags = 0; - - ret = sigaction(SIGBUS, &act, &oldact); - if (ret) { - error_setg_errno(errp, errno, - "os_mem_prealloc: failed to install signal handler"); - return; + /* + * Sense on every invocation, as MADV_POPULATE_WRITE cannot be used for + * some special mappings, such as mapping /dev/mem. + */ + use_madv_populate_write = madv_populate_write_possible(area, hpagesize); + + if (!use_madv_populate_write) { + memset(&act, 0, sizeof(act)); + act.sa_handler = &sigbus_handler; + act.sa_flags = 0; + + ret = sigaction(SIGBUS, &act, &oldact); + if (ret) { + error_setg_errno(errp, errno, + "os_mem_prealloc: failed to install signal handler"); + return; + } } /* touch pages simultaneously */ - ret = touch_all_pages(area, hpagesize, numpages, smp_cpus); + ret = touch_all_pages(area, hpagesize, numpages, smp_cpus, + use_madv_populate_write); if (ret) { error_setg_errno(errp, -ret, "os_mem_prealloc: preallocating memory failed"); } - ret = sigaction(SIGBUS, &oldact, NULL); - if (ret) { - /* Terminate QEMU since it can't recover from error */ - perror("os_mem_prealloc: failed to reinstall signal handler"); - exit(1); + if (!use_madv_populate_write) { + ret = sigaction(SIGBUS, &oldact, NULL); + if (ret) { + /* Terminate QEMU since it can't recover from error */ + perror("os_mem_prealloc: failed to reinstall signal handler"); + exit(1); + } } } -- 2.31.1