From patchwork Fri Mar 5 10:16:33 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 1447750 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=O0WvWOz2; dkim-atps=neutral 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 ozlabs.org (Postfix) with ESMTPS id 4DsP0Y1Hqqz9sVt for ; Fri, 5 Mar 2021 21:21:33 +1100 (AEDT) Received: from localhost ([::1]:47832 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lI7aN-0000zE-4B for incoming@patchwork.ozlabs.org; Fri, 05 Mar 2021 05:21:31 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:46492) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lI7XS-0006Wr-Lq for qemu-devel@nongnu.org; Fri, 05 Mar 2021 05:18:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26326) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lI7XH-0000mX-6r for qemu-devel@nongnu.org; Fri, 05 Mar 2021 05:18:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614939498; 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=f6uIF4mOL/litu0vcY7WaZzdmeX0GKRis7Naz8D8lrk=; b=O0WvWOz21qfQtWExCZvAH/BzXkw5sfNS+GocGh7tF6nfVWP4L2KHVRuwezGmunAqfiznNH ihnPhVSB54p8cF8G4KoD38j0FCgklNr8u7fvp53y6VWQ71DR41ME71e1VooJg+RxovzS91 N/N5k99XTZyHxNlbQkaJa8IUWtPcdMo= 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-316-bqYodLYyOWy9YABiCEsypA-1; Fri, 05 Mar 2021 05:18:17 -0500 X-MC-Unique: bqYodLYyOWy9YABiCEsypA-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 7C0E887A826; Fri, 5 Mar 2021 10:18:15 +0000 (UTC) Received: from t480s.redhat.com (ovpn-112-194.ams2.redhat.com [10.36.112.194]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7D3F81001B2C; Fri, 5 Mar 2021 10:17:59 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v2 8/9] util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE Date: Fri, 5 Mar 2021 11:16:33 +0100 Message-Id: <20210305101634.10745-9-david@redhat.com> In-Reply-To: <20210305101634.10745-1-david@redhat.com> References: <20210305101634.10745-1-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 Received-SPF: pass client-ip=63.128.21.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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: Juan Quintela , Murilo Opsfelder Araujo , Cornelia Huck , Eduardo Habkost , "Michael S. Tsirkin" , Stefan Weil , David Hildenbrand , 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+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" Let's support RAM_NORESERVE via MAP_NORESERVE. At least on Linux, the flag has no effect on shared mappings - except for hugetlbfs. 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 | 74 ++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 71 insertions(+), 4 deletions(-) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index 768e462529..3e85ca8898 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -2224,6 +2224,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length) abort(); } else { flags = MAP_FIXED; + flags |= (block->flags & RAM_NORESERVE) ? MAP_NORESERVE : 0; if (block->fd >= 0) { flags |= (block->flags & RAM_SHARED ? MAP_SHARED : MAP_PRIVATE); diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c index 397cb20a76..29c7a5035b 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 @@ -120,7 +121,8 @@ static void *mmap_reserve(size_t size, int fd) * it accessible. */ static void *mmap_activate(void *ptr, size_t size, int fd, bool readonly, - bool shared, bool is_pmem, off_t map_offset) + bool shared, bool is_pmem, bool noreserve, + off_t map_offset) { const int prot = PROT_READ | (readonly ? 0 : PROT_WRITE); int map_sync_flags = 0; @@ -129,6 +131,7 @@ static void *mmap_activate(void *ptr, size_t size, int fd, bool readonly, 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; } @@ -171,6 +174,70 @@ 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, bool readonly, bool shared) +{ +#if defined(__linux__) + gchar *content = NULL; + const char *endptr; + unsigned int tmp; + + /* + * Shared anonymous memory -- for sharing memory with forked children -- + * behaves in weird ways (i.e., in respect to memory accounting) and QEMU + * fortunately doesn't make use of it for guest RAM. Let's assert it + * remains that way. + */ + g_assert(!shared || fd >= 0); + + /* + * hugeltbfs 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. + */ + if (readonly || shared) { + 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 + return true; +#endif +} + void *qemu_ram_mmap(int fd, size_t size, size_t align, @@ -184,8 +251,7 @@ void *qemu_ram_mmap(int fd, size_t offset, total; void *ptr, *guardptr; - if (noreserve) { - error_report("Skipping reservation of swap space is not supported"); + if (noreserve && !map_noreserve_effective(fd, shared, readonly)) { return MAP_FAILED; } @@ -207,7 +273,7 @@ void *qemu_ram_mmap(int fd, offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; ptr = mmap_activate(guardptr + offset, size, fd, readonly, shared, is_pmem, - map_offset); + noreserve, map_offset); if (ptr == MAP_FAILED) { munmap(guardptr, total); return MAP_FAILED;