On Fri, Feb 16, 2018 at 01:15:59PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
>
> Use a flag on the RAMBlock to state whether it has the
> UFFDIO_ZEROPAGE capability, use it when it's available.
>
> This allows the use of postcopy on tmpfs as well as hugepage
> backed files.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
> exec.c | 15 +++++++++++++++
> include/exec/cpu-common.h | 3 +++
> migration/postcopy-ram.c | 13 ++++++++++---
> 3 files changed, 28 insertions(+), 3 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 0ec73bc917..1dc15298c2 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -99,6 +99,11 @@ static MemoryRegion io_mem_unassigned;
> */
> #define RAM_RESIZEABLE (1 << 2)
>
> +/* UFFDIO_ZEROPAGE is available on this RAMBlock to atomically
> + * zero the page and wake waiting processes.
> + * (Set during postcopy)
> + */
> +#define RAM_UF_ZEROPAGE (1 << 3)
> #endif
>
> #ifdef TARGET_PAGE_BITS_VARY
> @@ -1767,6 +1772,16 @@ bool qemu_ram_is_shared(RAMBlock *rb)
> return rb->flags & RAM_SHARED;
> }
>
> +bool qemu_ram_is_uf_zeroable(RAMBlock *rb)
> +{
> + return rb->flags & RAM_UF_ZEROPAGE;
> +}
> +
> +void qemu_ram_set_uf_zeroable(RAMBlock *rb)
> +{
> + rb->flags |= RAM_UF_ZEROPAGE;
> +}
> +
> /* Called with iothread lock held. */
> void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState
> *dev)
> {
> diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
> index 0d861a6289..24d335f95d 100644
> --- a/include/exec/cpu-common.h
> +++ b/include/exec/cpu-common.h
> @@ -73,6 +73,9 @@ void qemu_ram_set_idstr(RAMBlock *block, const char *name,
> DeviceState *dev);
> void qemu_ram_unset_idstr(RAMBlock *block);
> const char *qemu_ram_get_idstr(RAMBlock *rb);
> bool qemu_ram_is_shared(RAMBlock *rb);
> +bool qemu_ram_is_uf_zeroable(RAMBlock *rb);
> +void qemu_ram_set_uf_zeroable(RAMBlock *rb);
> +
> size_t qemu_ram_pagesize(RAMBlock *block);
> size_t qemu_ram_pagesize_largest(void);
>
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index bec6c2c66b..6297979700 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -490,6 +490,10 @@ static int ram_block_enable_notify(const char
> *block_name, void *host_addr,
> error_report("%s userfault: Region doesn't support COPY", __func__);
> return -1;
> }
> + if (reg_struct.ioctls & ((__u64)1 << _UFFDIO_ZEROPAGE)) {
> + RAMBlock *rb = qemu_ram_block_by_name(block_name);
> + qemu_ram_set_uf_zeroable(rb);
> + }
So the zeroable flag is only set after a listening operation of
postcopy migration. One thing I am a bit worried is that if someone
else wants to use the flag for a RAMBlock he/she may not notice this.
Say, qemu_ram_is_uf_zeroable() is not valid if there is no such an
incoming postcopy migration.
Maybe worth add a comment in the flag definition about this?
Not a big deal (considering that I see no potential QEMU user for
userfaultfd in short peroid), so no matter what:
Reviewed-by: Peter Xu <pet...@redhat.com>
>
> return 0;
> }
> @@ -699,11 +703,14 @@ int postcopy_place_page(MigrationIncomingState *mis,
> void *host, void *from,
> int postcopy_place_page_zero(MigrationIncomingState *mis, void *host,
> RAMBlock *rb)
> {
> + size_t pagesize = qemu_ram_pagesize(rb);
> trace_postcopy_place_page_zero(host);
>
> - if (qemu_ram_pagesize(rb) == getpagesize()) {
> - if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, NULL, getpagesize(),
> - rb)) {
> + /* Normal RAMBlocks can zero a page using UFFDIO_ZEROPAGE
> + * but it's not available for everything (e.g. hugetlbpages)
> + */
> + if (qemu_ram_is_uf_zeroable(rb)) {
> + if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, NULL, pagesize,
> rb)) {
> int e = errno;
> error_report("%s: %s zero host: %p",
> __func__, strerror(e), host);
> --
> 2.14.3
>
--
Peter Xu
