migration/multifd-zero-page.c

   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 }