"Dr. David Alan Gilbert (git)" <dgilb...@redhat.com> wrote:
> From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
>
> In postcopy, the destination guest is running at the same time
> as it's receiving pages; as we receive new pages we must put
> them into the guests address space atomically to avoid a running
> CPU accessing a partially written page.
>
> Use the helpers in postcopy-ram.c to map these pages.
>
> qemu_get_buffer_in_place is used to avoid a copy out of qemu_file
> in the case that postcopy is going to do a copy anyway.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
> migration/ram.c | 128
> +++++++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 103 insertions(+), 25 deletions(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 487e838..6d9cfb5 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1848,7 +1848,17 @@ static int load_xbzrle(QEMUFile *f, ram_addr_t addr,
> void *host)
> /* Must be called from within a rcu critical section.
> * Returns a pointer from within the RCU-protected ram_list.
> */
> +/*
> + * Read a RAMBlock ID from the stream f, find the host address of the
> + * start of that block and add on 'offset'
> + *
> + * f: Stream to read from
> + * mis: MigrationIncomingState
> + * offset: Offset within the block
> + * flags: Page flags (mostly to see if it's a continuation of previous block)
> + */
> static inline void *host_from_stream_offset(QEMUFile *f,
> + MigrationIncomingState *mis,
> ram_addr_t offset,
> int flags)
> {
Uh, oh, we change the prototype of host_from_stream_offset() but not the
function itself? Strange, no?
> + postcopy_place_needed = false;
> + if (flags & (RAM_SAVE_FLAG_COMPRESS | RAM_SAVE_FLAG_PAGE |
> + RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
> + host = host_from_stream_offset(f, mis, addr, flags);
> + if (!host) {
> + error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
> + ret = -EINVAL;
> + break;
> + }
> + page_buffer = host;
You can move this bit of code here in a different patch, makes review easier.
all_zero can also be on that patch.
> + if (postcopy_running) {
As discussed on irc, I still think that having a RAM_SAVE_HOST_PAGE make
everything much, much clearer and easier, but I agree that is not
trivial with current code.
You are reusingh ram_load, but have lots and lots of
if (postcopy_running) {
} else {
}
I think that it would be easier to just have:
if (postcopy_running) {
ram_load_postcopy()
} else {
ram_load_precopy{}
}
You duplicate a bit of code, but remove lots of ifs from the equation,
not sure which one is really easier. I just hate bits like the
following one.
> @@ -2062,32 +2123,36 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> }
> break;
> case RAM_SAVE_FLAG_COMPRESS:
> ch = qemu_get_byte(f);
> - ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
> + if (!postcopy_running) {
> + ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
> + } else {
> + memset(page_buffer, ch, TARGET_PAGE_SIZE);
> + if (ch) {
> + all_zero = false;
> + }
> + }
> @@ -2123,6 +2188,19 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> ret = -EINVAL;
> }
> }
> +
> + if (postcopy_place_needed) {
> + /* This gets called at the last target page in the host page */
> + if (!all_zero) {
> + ret = postcopy_place_page(mis, host + TARGET_PAGE_SIZE -
> + qemu_host_page_size,
> + postcopy_place_source);
> + } else {
> + ret = postcopy_place_page_zero(mis,
> + host + TARGET_PAGE_SIZE -
> + qemu_host_page_size);
> + }
> + }
Hahahaha, just change the if or the variable name.
having a
if (!cond) {
f1();
} else {
f2();
}
makes no sense, better to have
if (cond) {
f2()
} else {
f1()
}
no?
The patch itself is ok.
Thanks, Juan.
