tree 13341c1b1fcd6d4eeb39576c75417cccbcdee748
parent c332c83ae736c72dcf072e96e98a774fce39e722
author Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> 1272448236 +0900
committer Avi Kivity <avi@redhat.com> 1280648127 +0300

KVM: x86: avoid unnecessary bitmap allocation when memslot is clean

Although we always allocate a new dirty bitmap in x86's get_dirty_log(),
it is only used as a zero-source of copy_to_user() and freed right after
that when memslot is clean. This patch uses clear_user() instead of doing
this unnecessary zero-source allocation.

Performance improvement: as we can expect easily, the time needed to
allocate a bitmap is completely reduced. In my test, the improved ioctl
was about 4 to 10 times faster than the original one for clean slots.
Furthermore, reducing memory allocations and copies will produce good
effects to caches too.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>