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Re: [PATCH RFC 04/15] migration: Add postcopy_has_request()
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH RFC 04/15] migration: Add postcopy_has_request() |
Date: |
Wed, 19 Jan 2022 14:27:26 +0000 |
User-agent: |
Mutt/2.1.5 (2021-12-30) |
* Peter Xu (peterx@redhat.com) wrote:
> Add a helper to detect whether postcopy has pending request.
>
> Since at it, cleanup the code a bit, e.g. in unqueue_page() we shouldn't need
> to check it again on queue empty because we're the only one (besides cleanup
> code, which should never run during this process) that will take a request off
> the list, so the request list can only grow but not shrink under the hood.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
> migration/ram.c | 45 ++++++++++++++++++++++++++++-----------------
> 1 file changed, 28 insertions(+), 17 deletions(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 94b0ad4234..dc6ba041fa 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -354,6 +354,12 @@ static RAMState *ram_state;
>
> static NotifierWithReturnList precopy_notifier_list;
>
> +/* Whether postcopy has queued requests? */
> +static bool postcopy_has_request(RAMState *rs)
> +{
> + return !QSIMPLEQ_EMPTY_ATOMIC(&rs->src_page_requests);
> +}
> +
> void precopy_infrastructure_init(void)
> {
> notifier_with_return_list_init(&precopy_notifier_list);
> @@ -1533,28 +1539,33 @@ static bool find_dirty_block(RAMState *rs,
> PageSearchStatus *pss, bool *again)
> */
> static RAMBlock *unqueue_page(RAMState *rs, ram_addr_t *offset)
> {
> + struct RAMSrcPageRequest *entry;
> RAMBlock *block = NULL;
>
> - if (QSIMPLEQ_EMPTY_ATOMIC(&rs->src_page_requests)) {
> + if (!postcopy_has_request(rs)) {
> return NULL;
> }
>
> QEMU_LOCK_GUARD(&rs->src_page_req_mutex);
> - if (!QSIMPLEQ_EMPTY(&rs->src_page_requests)) {
> - struct RAMSrcPageRequest *entry =
> - QSIMPLEQ_FIRST(&rs->src_page_requests);
> - block = entry->rb;
> - *offset = entry->offset;
> -
> - if (entry->len > TARGET_PAGE_SIZE) {
> - entry->len -= TARGET_PAGE_SIZE;
> - entry->offset += TARGET_PAGE_SIZE;
> - } else {
> - memory_region_unref(block->mr);
> - QSIMPLEQ_REMOVE_HEAD(&rs->src_page_requests, next_req);
> - g_free(entry);
> - migration_consume_urgent_request();
> - }
> +
> + /*
> + * This should _never_ change even after we take the lock, because no one
> + * should be taking anything off the request list other than us.
> + */
> + assert(postcopy_has_request(rs));
> +
> + entry = QSIMPLEQ_FIRST(&rs->src_page_requests);
> + block = entry->rb;
> + *offset = entry->offset;
> +
> + if (entry->len > TARGET_PAGE_SIZE) {
> + entry->len -= TARGET_PAGE_SIZE;
> + entry->offset += TARGET_PAGE_SIZE;
> + } else {
> + memory_region_unref(block->mr);
> + QSIMPLEQ_REMOVE_HEAD(&rs->src_page_requests, next_req);
> + g_free(entry);
> + migration_consume_urgent_request();
> }
>
> return block;
> @@ -2996,7 +3007,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
> t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> i = 0;
> while ((ret = qemu_file_rate_limit(f)) == 0 ||
> - !QSIMPLEQ_EMPTY(&rs->src_page_requests)) {
> + postcopy_has_request(rs)) {
> int pages;
>
> if (qemu_file_get_error(f)) {
> --
> 2.32.0
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
- [PATCH RFC 01/15] migration: No off-by-one for pss->page update in host page size, (continued)
- [PATCH RFC 01/15] migration: No off-by-one for pss->page update in host page size, Peter Xu, 2022/01/19
- [PATCH RFC 03/15] migration: Enable UFFD_FEATURE_THREAD_ID even without blocktime feat, Peter Xu, 2022/01/19
- [PATCH RFC 02/15] migration: Allow pss->page jump over clean pages, Peter Xu, 2022/01/19
- [PATCH RFC 04/15] migration: Add postcopy_has_request(), Peter Xu, 2022/01/19
- [PATCH RFC 05/15] migration: Simplify unqueue_page(), Peter Xu, 2022/01/19
- Re: [PATCH RFC 05/15] migration: Simplify unqueue_page(), Juan Quintela, 2022/01/27
- [PATCH RFC 06/15] migration: Move temp page setup and cleanup into separate functions, Peter Xu, 2022/01/19
- [PATCH RFC 07/15] migration: Introduce postcopy channels on dest node, Peter Xu, 2022/01/19