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 X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 446EBC43461 for ; Mon, 10 May 2021 11:51:41 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id CA28361421 for ; Mon, 10 May 2021 11:51:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CA28361421 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35978 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lg4Rn-0006D0-TB for qemu-devel@archiver.kernel.org; Mon, 10 May 2021 07:51:39 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57318) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lg4Kq-00012h-HA for qemu-devel@nongnu.org; Mon, 10 May 2021 07:44:28 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:25146) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lg4Km-0003pN-CY for qemu-devel@nongnu.org; Mon, 10 May 2021 07:44:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620647063; 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=Q83OtAetkgZ7UQqRuJxlLuDbdvHopk4FRWRZ1JgAx6A=; b=BzH3WfPUxeShSW3dRBtqao57mNoVjDwAVtYY4R53MVoPzovjfltp/H8cwvb6y65r1tr9f6 kyhBlZUyK25Ly5r8gfrlkck+286btlAQ4wEv4xLw2colkLzX3sUt7rzwn8tH04y6fe5XvI U5HUaZwdNRXA55T9Qm/TkRv4O9GLgnM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-346-6_E_XYKuOC-Z6c7XOO91Yw-1; Mon, 10 May 2021 07:44:21 -0400 X-MC-Unique: 6_E_XYKuOC-Z6c7XOO91Yw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8C27810066E5 for ; Mon, 10 May 2021 11:44:20 +0000 (UTC) Received: from t480s.redhat.com (ovpn-114-137.ams2.redhat.com [10.36.114.137]) by smtp.corp.redhat.com (Postfix) with ESMTP id 434071037F20; Mon, 10 May 2021 11:44:19 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v8 09/15] util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE under Linux Date: Mon, 10 May 2021 13:43:22 +0200 Message-Id: <20210510114328.21835-10-david@redhat.com> In-Reply-To: <20210510114328.21835-1-david@redhat.com> References: <20210510114328.21835-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" 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=-0.698, 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_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: Eduardo Habkost , Peter Xu , David Hildenbrand Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Let's support RAM_NORESERVE via MAP_NORESERVE on Linux. The flag has no effect on most shared mappings - except for hugetlbfs and anonymous memory. Linux man page: "MAP_NORESERVE: Do not reserve swap space for this mapping. When swap space is reserved, one has the guarantee that it is possible to modify the mapping. When swap space is not reserved one might get SIGSEGV upon a write if no physical memory is available. See also the discussion of the file /proc/sys/vm/overcommit_memory in proc(5). In kernels before 2.6, this flag had effect only for private writable mappings." Note that the "guarantee" part is wrong with memory overcommit in Linux. Also, in Linux hugetlbfs is treated differently - we configure reservation of huge pages from the pool, not reservation of swap space (huge pages cannot be swapped). The rough behavior is [1]: a) !Hugetlbfs: 1) Without MAP_NORESERVE *or* with memory overcommit under Linux disabled ("/proc/sys/vm/overcommit_memory == 2"), the following accounting/reservation happens: For a file backed map SHARED or READ-only - 0 cost (the file is the map not swap) PRIVATE WRITABLE - size of mapping per instance For an anonymous or /dev/zero map SHARED - size of mapping PRIVATE READ-only - 0 cost (but of little use) PRIVATE WRITABLE - size of mapping per instance 2) With MAP_NORESERVE, no accounting/reservation happens. b) Hugetlbfs: 1) Without MAP_NORESERVE, huge pages are reserved. 2) With MAP_NORESERVE, no huge pages are reserved. Note: With "/proc/sys/vm/overcommit_memory == 0", we were already able to configure it for !hugetlbfs globally; this toggle now allows configuring it more fine-grained, not for the whole system. The target use case is virtio-mem, which dynamically exposes memory inside a large, sparse memory area to the VM. [1] https://www.kernel.org/doc/Documentation/vm/overcommit-accounting Reviewed-by: Peter Xu Acked-by: Eduardo Habkost for memory backend and machine core Signed-off-by: David Hildenbrand --- include/qemu/osdep.h | 3 ++ softmmu/physmem.c | 1 + util/mmap-alloc.c | 69 ++++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 71 insertions(+), 2 deletions(-) diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index af65b36698..0a7384d15c 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -195,6 +195,9 @@ extern "C" { #ifndef MAP_FIXED_NOREPLACE #define MAP_FIXED_NOREPLACE 0 #endif +#ifndef MAP_NORESERVE +#define MAP_NORESERVE 0 +#endif #ifndef ENOMEDIUM #define ENOMEDIUM ENODEV #endif diff --git a/softmmu/physmem.c b/softmmu/physmem.c index a356c3fc09..a8394acc3a 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -2227,6 +2227,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length) flags = MAP_FIXED; flags |= block->flags & RAM_SHARED ? MAP_SHARED : MAP_PRIVATE; + flags |= block->flags & RAM_NORESERVE ? MAP_NORESERVE : 0; if (block->fd >= 0) { area = mmap(vaddr, length, PROT_READ | PROT_WRITE, flags, block->fd, offset); diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c index d0cf4aaee5..838e286ce5 100644 --- a/util/mmap-alloc.c +++ b/util/mmap-alloc.c @@ -20,6 +20,7 @@ #include "qemu/osdep.h" #include "qemu/mmap-alloc.h" #include "qemu/host-utils.h" +#include "qemu/cutils.h" #include "qemu/error-report.h" #define HUGETLBFS_MAGIC 0x958458f6 @@ -83,6 +84,70 @@ size_t qemu_mempath_getpagesize(const char *mem_path) return qemu_real_host_page_size; } +#define OVERCOMMIT_MEMORY_PATH "/proc/sys/vm/overcommit_memory" +static bool map_noreserve_effective(int fd, uint32_t qemu_map_flags) +{ +#if defined(__linux__) + const bool readonly = qemu_map_flags & QEMU_MAP_READONLY; + const bool shared = qemu_map_flags & QEMU_MAP_SHARED; + gchar *content = NULL; + const char *endptr; + unsigned int tmp; + + /* + * hugeltb accounting is different than ordinary swap reservation: + * a) Hugetlb pages from the pool are reserved for both private and + * shared mappings. For shared mappings, all mappers have to specify + * MAP_NORESERVE. + * b) MAP_NORESERVE is not affected by /proc/sys/vm/overcommit_memory. + */ + if (qemu_fd_getpagesize(fd) != qemu_real_host_page_size) { + return true; + } + + /* + * Accountable mappings in the kernel that can be affected by MAP_NORESEVE + * are private writable mappings (see mm/mmap.c:accountable_mapping() in + * Linux). For all shared or readonly mappings, MAP_NORESERVE is always + * implicitly active -- no reservation; this includes shmem. The only + * exception is shared anonymous memory, it is accounted like private + * anonymous memory. + */ + if (readonly || (shared && fd >= 0)) { + return true; + } + + /* + * MAP_NORESERVE is globally ignored for applicable !hugetlb mappings when + * memory overcommit is set to "never". Sparse memory regions aren't really + * possible in this system configuration. + * + * Bail out now instead of silently committing way more memory than + * currently desired by the user. + */ + if (g_file_get_contents(OVERCOMMIT_MEMORY_PATH, &content, NULL, NULL) && + !qemu_strtoui(content, &endptr, 0, &tmp) && + (!endptr || *endptr == '\n')) { + if (tmp == 2) { + error_report("Skipping reservation of swap space is not supported:" + " \"" OVERCOMMIT_MEMORY_PATH "\" is \"2\""); + return false; + } + return true; + } + /* this interface has been around since Linux 2.6 */ + error_report("Skipping reservation of swap space is not supported:" + " Could not read: \"" OVERCOMMIT_MEMORY_PATH "\""); + return false; +#endif + /* + * E.g., FreeBSD used to define MAP_NORESERVE, never implemented it, + * and removed it a while ago. + */ + error_report("Skipping reservation of swap space is not supported"); + return false; +} + /* * Reserve a new memory region of the requested size to be used for mapping * from the given fd (if any). @@ -131,13 +196,13 @@ static void *mmap_activate(void *ptr, size_t size, int fd, int flags = MAP_FIXED; void *activated_ptr; - if (noreserve) { - error_report("Skipping reservation of swap space is not supported"); + if (noreserve && !map_noreserve_effective(fd, qemu_map_flags)) { return MAP_FAILED; } flags |= fd == -1 ? MAP_ANONYMOUS : 0; flags |= shared ? MAP_SHARED : MAP_PRIVATE; + flags |= noreserve ? MAP_NORESERVE : 0; if (shared && sync) { map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; } -- 2.30.2