migration: drop MADVISE_DONT_NEED for incoming zero pages

The madvise for zeroed out pages was introduced when every transferred zero page was memset to zero and thus allocated. Since commit 211ea74 we check for zeroness of a target page before we memset it to zero. Additionally we memmap target memory so it is essentially zero initialized (except for e.g. option roms and bios which are loaded into target memory although they shouldn't). It was reported recently that this madvise causes a performance degradation in some situations. As the madvise should only be called rarely and if it's called it is likely on a busy page (it was non-zero and changed to zero during migration) drop it completely. Reported-By: Zhang Haoyu <[email protected]> Acked-by: Paolo Bonzini <[email protected]> Signed-off-by: Peter Lieven <[email protected]> Signed-off-by: Juan Quintela <[email protected]>
dannf · Nov 19, 2013 · fc1c4a5 · fc1c4a5
1 parent 5c5432e
commit fc1c4a5
Showing 1 changed file with 0 additions and 8 deletions.
diff --git a/arch_init.c b/arch_init.c
@@ -850,14 +850,6 @@ void ram_handle_compressed(void *host, uint8_t ch, uint64_t size)
 {
     if (ch != 0 || !is_zero_range(host, size)) {
         memset(host, ch, size);
-#ifndef _WIN32
-        if (ch == 0 && (!kvm_enabled() || kvm_has_sync_mmu())) {
-            size = size & ~(getpagesize() - 1);
-            if (size > 0) {
-                qemu_madvise(host, size, QEMU_MADV_DONTNEED);
-            }
-        }
-#endif
     }
 }