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=-20.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 C969EC433DB for ; Wed, 10 Mar 2021 10:33:31 +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 5807164F74 for ; Wed, 10 Mar 2021 10:33:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5807164F74 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]:43304 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lJw9i-0007Cn-AE for qemu-devel@archiver.kernel.org; Wed, 10 Mar 2021 05:33:30 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:37778) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lJw5X-00036r-Fp for qemu-devel@nongnu.org; Wed, 10 Mar 2021 05:29:11 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23317) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lJw5U-0008Rc-D5 for qemu-devel@nongnu.org; Wed, 10 Mar 2021 05:29:11 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615372147; 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=q+9ruO+lsPVCnistGF7gVdnqH0r/SJhW5KWVWk6jPEQ=; b=BOVNXcsHHEXAkNVniJ+JEQy9mjL0WDqshFl5qWA0HzuJE8AAF+ikT1MlMRoJoAIz6CjvoG tBJx6TBoSh/OWf6pCQxzUwh3T89PY/RuOfacqP1Ss3c6BHESLXtvgA9Grs3/LPDYvasI9A IU4hPxshd89/wMRxtBVPVpV3GCY6tqs= 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-481-rL9C--A4Nga6xWqKg0CPmw-1; Wed, 10 Mar 2021 05:29:04 -0500 X-MC-Unique: rL9C--A4Nga6xWqKg0CPmw-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 27A7D1932481; Wed, 10 Mar 2021 10:29:02 +0000 (UTC) Received: from [10.36.114.87] (ovpn-114-87.ams2.redhat.com [10.36.114.87]) by smtp.corp.redhat.com (Postfix) with ESMTP id C19B51037E82; Wed, 10 Mar 2021 10:28:57 +0000 (UTC) Subject: Re: [PATCH v3 11/12] util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE To: qemu-devel@nongnu.org References: <20210308150600.14440-1-david@redhat.com> <20210308150600.14440-12-david@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Wed, 10 Mar 2021 11:28:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210308150600.14440-12-david@redhat.com> 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-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.251, 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_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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juan Quintela , Marcel Apfelbaum , Cornelia Huck , Eduardo Habkost , "Michael S. Tsirkin" , Stefan Weil , Murilo Opsfelder Araujo , Richard Henderson , "Dr. David Alan Gilbert" , Peter Xu , Greg Kurz , Halil Pasic , Christian Borntraeger , Stefan Hajnoczi , Igor Mammedov , Thomas Huth , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Igor Kotrasinski Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 08.03.21 16:05, David Hildenbrand wrote: > Let's support RAM_NORESERVE via MAP_NORESERVE. At least 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 > > Signed-off-by: David Hildenbrand > --- > softmmu/physmem.c | 1 + > util/mmap-alloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 66 insertions(+), 1 deletion(-) > > diff --git a/softmmu/physmem.c b/softmmu/physmem.c > index dcc1fb74aa..199c5a4985 100644 > --- a/softmmu/physmem.c > +++ b/softmmu/physmem.c > @@ -2229,6 +2229,7 @@ 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 ecace41ad5..c511a68bbe 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 > @@ -125,6 +126,7 @@ static void *mmap_activate(void *ptr, size_t size, int fd, uint32_t mmap_flags, > const bool readonly = mmap_flags & QEMU_RAM_MMAP_READONLY; > const bool shared = mmap_flags & QEMU_RAM_MMAP_SHARED; > const bool is_pmem = mmap_flags & QEMU_RAM_MMAP_PMEM; > + const bool noreserve = mmap_flags & QEMU_RAM_MMAP_NORESERVE; > const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE); > int map_sync_flags = 0; > int flags = MAP_FIXED; > @@ -132,6 +134,7 @@ static void *mmap_activate(void *ptr, size_t size, int fd, uint32_t mmap_flags, > > flags |= fd == -1 ? MAP_ANONYMOUS : 0; > flags |= shared ? MAP_SHARED : MAP_PRIVATE; > + flags |= noreserve ? MAP_NORESERVE : 0; > if (shared && is_pmem) { > map_sync_flags = MAP_SYNC | MAP_SHARED_VALIDATE; > } > @@ -174,6 +177,66 @@ static inline size_t mmap_guard_pagesize(int fd) > #endif > } > > +#define OVERCOMMIT_MEMORY_PATH "/proc/sys/vm/overcommit_memory" > +static bool map_noreserve_effective(int fd, uint32_t mmap_flags) > +{ > +#if defined(__linux__) > + const bool readonly = mmap_flags & QEMU_RAM_MMAP_READONLY; > + const bool shared = mmap_flags & QEMU_RAM_MMAP_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, reservations are tracked > + * per file -- 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 private writable mappings when > + * 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; > +#else I'll return "false" here for now after learning that e.g., FreeBSD never implemented the flag and removed it a while ago https://github.com/Clozure/ccl/issues/17 So I'll unlock it only for Linux - which makes sense, because I only test there (and only care about Linux with MAP_NORESERVE) > + return true; -- Thanks, David / dhildenb