d5cd94bbaf
Implement 'fixed-ram' feature. The core of the feature is to ensure that each ram page of the migration stream has a specific offset in the resulting migration stream. The reason why we'd want such behavior are two fold: - When doing a 'fixed-ram' migration the resulting file will have a bounded size, since pages which are dirtied multiple times will always go to a fixed location in the file, rather than constantly being added to a sequential stream. This eliminates cases where a vm with, say, 1g of ram can result in a migration file that's 10s of Gbs, provided that the workload constantly redirties memory. - It paves the way to implement DIO-enabled save/restore of the migration stream as the pages are ensured to be written at aligned offsets. The features requires changing the format. First, a bitmap is introduced which tracks which pages have been written (i.e are dirtied) during migration and subsequently it's being written in the resultin file, again at a fixed location for every ramblock. Zero pages are ignored as they'd be zero in the destination migration as well. With the changed format data would look like the following: |name len|name|used_len|pc*|bitmap_size|pages_offset|bitmap|pages| * pc - refers to the page_size/mr->addr members, so newly added members begin from "bitmap_size". This layout is initialized during ram_save_setup so instead of having a sequential stream of pages that follow the ramblock headers the dirty pages for a ramblock follow its header. Since all pages have a fixed location RAM_SAVE_FLAG_EOS is no longer generated on every migration iteration but there is effectively a single RAM_SAVE_FLAG_EOS right at the end. Signed-off-by: Nikolay Borisov <nborisov@suse.com>
88 lines
2.9 KiB
C
88 lines
2.9 KiB
C
/*
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* Declarations for cpu physical memory functions
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*
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* Copyright 2011 Red Hat, Inc. and/or its affiliates
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*
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* Authors:
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* Avi Kivity <avi@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or
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* later. See the COPYING file in the top-level directory.
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*
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*/
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/*
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* This header is for use by exec.c and memory.c ONLY. Do not include it.
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* The functions declared here will be removed soon.
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*/
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#ifndef QEMU_EXEC_RAMBLOCK_H
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#define QEMU_EXEC_RAMBLOCK_H
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#ifndef CONFIG_USER_ONLY
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#include "cpu-common.h"
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#include "qemu/rcu.h"
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#include "exec/ramlist.h"
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struct RAMBlock {
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struct rcu_head rcu;
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struct MemoryRegion *mr;
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uint8_t *host;
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uint8_t *colo_cache; /* For colo, VM's ram cache */
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ram_addr_t offset;
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ram_addr_t used_length;
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ram_addr_t max_length;
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void (*resized)(const char*, uint64_t length, void *host);
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uint32_t flags;
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/* Protected by iothread lock. */
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char idstr[256];
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/* RCU-enabled, writes protected by the ramlist lock */
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QLIST_ENTRY(RAMBlock) next;
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QLIST_HEAD(, RAMBlockNotifier) ramblock_notifiers;
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int fd;
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size_t page_size;
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/* dirty bitmap used during migration */
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unsigned long *bmap;
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/* shadow dirty bitmap used when migrating to a file */
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unsigned long *shadow_bmap;
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/*
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* offset in the file pages belonging to this ramblock are saved,
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* used only during migration to a file.
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*/
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off_t bitmap_offset;
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uint64_t pages_offset;
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/* bitmap of already received pages in postcopy */
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unsigned long *receivedmap;
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/*
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* bitmap to track already cleared dirty bitmap. When the bit is
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* set, it means the corresponding memory chunk needs a log-clear.
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* Set this up to non-NULL to enable the capability to postpone
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* and split clearing of dirty bitmap on the remote node (e.g.,
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* KVM). The bitmap will be set only when doing global sync.
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*
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* It is only used during src side of ram migration, and it is
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* protected by the global ram_state.bitmap_mutex.
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*
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* NOTE: this bitmap is different comparing to the other bitmaps
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* in that one bit can represent multiple guest pages (which is
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* decided by the `clear_bmap_shift' variable below). On
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* destination side, this should always be NULL, and the variable
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* `clear_bmap_shift' is meaningless.
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*/
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unsigned long *clear_bmap;
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uint8_t clear_bmap_shift;
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/*
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* RAM block length that corresponds to the used_length on the migration
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* source (after RAM block sizes were synchronized). Especially, after
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* starting to run the guest, used_length and postcopy_length can differ.
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* Used to register/unregister uffd handlers and as the size of the received
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* bitmap. Receiving any page beyond this length will bail out, as it
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* could not have been valid on the source.
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*/
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ram_addr_t postcopy_length;
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};
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#endif
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#endif
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