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migration/ram: Factor out populating pages readable in ram_block_populate_pages()

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Let's factor out prefaulting/populating to make further changes easier to
review and add a comment what we are actually expecting to happen. While at
it, use the actual page size of the ramblock, which defaults to
qemu_real_host_page_size for anonymous memory. Further, rename
ram_block_populate_pages() to ram_block_populate_read() as well, to make
it clearer what we are doing.

In the future, we might want to use MADV_POPULATE_READ to speed up
population.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
David Hildenbrand 2021-10-11 19:53:45 +02:00 committed by Juan Quintela
parent 7648297d40
commit f7b9dcfbcf
1 changed files with 22 additions and 13 deletions
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35
migration/ram.c
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@ -1639,26 +1639,35 @@ out:
return ret;
}
static inline void populate_read_range(RAMBlock *block, ram_addr_t offset,
ram_addr_t size)
{
/*
* We read one byte of each page; this will preallocate page tables if
* required and populate the shared zeropage on MAP_PRIVATE anonymous memory
* where no page was populated yet. This might require adaption when
* supporting other mappings, like shmem.
*/
for (; offset < size; offset += block->page_size) {
char tmp = *((char *)block->host + offset);
/* Don't optimize the read out */
asm volatile("" : "+r" (tmp));
}
}
/*
* ram_block_populate_pages: populate memory in the RAM block by reading
* an integer from the beginning of each page.
* ram_block_populate_read: preallocate page tables and populate pages in the
* RAM block by reading a byte of each page.
*
* Since it's solely used for userfault_fd WP feature, here we just
* hardcode page size to qemu_real_host_page_size.
*
* @block: RAM block to populate
*/
static void ram_block_populate_pages(RAMBlock *block)
static void ram_block_populate_read(RAMBlock *block)
{
char *ptr = (char *) block->host;
for (ram_addr_t offset = 0; offset < block->used_length;
offset += qemu_real_host_page_size) {
char tmp = *(ptr + offset);
/* Don't optimize the read out */
asm volatile("" : "+r" (tmp));
}
populate_read_range(block, 0, block->used_length);
}
/*
@ -1684,7 +1693,7 @@ void ram_write_tracking_prepare(void)
* UFFDIO_WRITEPROTECT_MODE_WP mode setting would silently skip
* pages with pte_none() entries in page table.
*/
ram_block_populate_pages(block);
ram_block_populate_read(block);
}
}