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migration: do not overwrite zero pages 

on incoming migration do not memset pages to zero if they already read as zero.
this will allocate a new zero page and consume memory unnecessarily. even
if we madvise a MADV_DONTNEED later this will only deallocate the memory
asynchronously.

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Peter Lieven 2013-06-10 12:14:20 +02:00 committed by Juan Quintela
parent 9ef051e553
commit 211ea74022
1 changed files with 8 additions and 6 deletions
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14
arch_init.c
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@ -835,14 +835,16 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
}
ch = qemu_get_byte(f);
memset(host, ch, TARGET_PAGE_SIZE);
if (ch != 0 || !is_zero_page(host)) {
memset(host, ch, TARGET_PAGE_SIZE);
#ifndef _WIN32
if (ch == 0 &&
(!kvm_enabled() || kvm_has_sync_mmu()) &&
getpagesize() <= TARGET_PAGE_SIZE) {
qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
}
if (ch == 0 &&
(!kvm_enabled() || kvm_has_sync_mmu()) &&
getpagesize() <= TARGET_PAGE_SIZE) {
qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
}
#endif
}
} else if (flags & RAM_SAVE_FLAG_PAGE) {
void *host;