1 /*
2  * Multifd zero page detection implementation.
3  *
4  * Copyright (c) 2024 Bytedance Inc
5  *
6  * Authors:
7  *  Hao Xiang <hao.xiang@bytedance.com>
8  *
9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
10  * See the COPYING file in the top-level directory.
11  */
12 
13 #include "qemu/osdep.h"
14 #include "qemu/cutils.h"
15 #include "exec/ramblock.h"
16 #include "migration.h"
17 #include "multifd.h"
18 #include "options.h"
19 #include "ram.h"
20 
21 static bool multifd_zero_page_enabled(void)
22 {
23     return migrate_zero_page_detection() == ZERO_PAGE_DETECTION_MULTIFD;
24 }
25 
26 static void swap_page_offset(ram_addr_t *pages_offset, int a, int b)
27 {
28     ram_addr_t temp;
29 
30     if (a == b) {
31         return;
32     }
33 
34     temp = pages_offset[a];
35     pages_offset[a] = pages_offset[b];
36     pages_offset[b] = temp;
37 }
38 
39 /**
40  * multifd_send_zero_page_detect: Perform zero page detection on all pages.
41  *
42  * Sorts normal pages before zero pages in p->pages->offset and updates
43  * p->pages->normal_num.
44  *
45  * @param p A pointer to the send params.
46  */
47 void multifd_send_zero_page_detect(MultiFDSendParams *p)
48 {
49     MultiFDPages_t *pages = p->pages;
50     RAMBlock *rb = pages->block;
51     int i = 0;
52     int j = pages->num - 1;
53 
54     if (!multifd_zero_page_enabled()) {
55         pages->normal_num = pages->num;
56         return;
57     }
58 
59     /*
60      * Sort the page offset array by moving all normal pages to
61      * the left and all zero pages to the right of the array.
62      */
63     while (i <= j) {
64         uint64_t offset = pages->offset[i];
65 
66         if (!buffer_is_zero(rb->host + offset, p->page_size)) {
67             i++;
68             continue;
69         }
70 
71         swap_page_offset(pages->offset, i, j);
72         ram_release_page(rb->idstr, offset);
73         j--;
74     }
75 
76     pages->normal_num = i;
77 }
78 
79 void multifd_recv_zero_page_process(MultiFDRecvParams *p)
80 {
81     for (int i = 0; i < p->zero_num; i++) {
82         void *page = p->host + p->zero[i];
83         if (!buffer_is_zero(page, p->page_size)) {
84             memset(page, 0, p->page_size);
85         }
86     }
87 }
88