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migration: Yield bitmap_mutex properly when sending/sleeping
Don't take the bitmap mutex when sending pages, or when being throttled by migration_rate_limit() (which is a bit tricky to call it here in ram code, but seems still helpful). It prepares for the possibility of concurrently sending pages in >1 threads using the function ram_save_host_page() because all threads may need the bitmap_mutex to operate on bitmaps, so that either sendmsg() or any kind of qemu_sem_wait() blocking for one thread will not block the other from progressing. Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Juan Quintela <quintela@redhat.com>
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@ -2452,9 +2452,14 @@ static void postcopy_preempt_reset_channel(RAMState *rs)
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* a host page in which case the remainder of the hostpage is sent.
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* Only dirty target pages are sent. Note that the host page size may
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* be a huge page for this block.
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*
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* The saving stops at the boundary of the used_length of the block
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* if the RAMBlock isn't a multiple of the host page size.
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*
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* The caller must be with ram_state.bitmap_mutex held to call this
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* function. Note that this function can temporarily release the lock, but
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* when the function is returned it'll make sure the lock is still held.
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*
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* Returns the number of pages written or negative on error
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*
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* @rs: current RAM state
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@ -2462,6 +2467,7 @@ static void postcopy_preempt_reset_channel(RAMState *rs)
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*/
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static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss)
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{
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bool page_dirty, preempt_active = postcopy_preempt_active();
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int tmppages, pages = 0;
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size_t pagesize_bits =
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qemu_ram_pagesize(pss->block) >> TARGET_PAGE_BITS;
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@ -2485,22 +2491,40 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss)
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break;
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}
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/* Check the pages is dirty and if it is send it */
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if (migration_bitmap_clear_dirty(rs, pss->block, pss->page)) {
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tmppages = ram_save_target_page(rs, pss);
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if (tmppages < 0) {
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return tmppages;
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}
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page_dirty = migration_bitmap_clear_dirty(rs, pss->block, pss->page);
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pages += tmppages;
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/* Check the pages is dirty and if it is send it */
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if (page_dirty) {
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/*
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* Allow rate limiting to happen in the middle of huge pages if
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* something is sent in the current iteration.
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* Properly yield the lock only in postcopy preempt mode
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* because both migration thread and rp-return thread can
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* operate on the bitmaps.
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*/
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if (pagesize_bits > 1 && tmppages > 0) {
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migration_rate_limit();
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if (preempt_active) {
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qemu_mutex_unlock(&rs->bitmap_mutex);
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}
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tmppages = ram_save_target_page(rs, pss);
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if (tmppages >= 0) {
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pages += tmppages;
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/*
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* Allow rate limiting to happen in the middle of huge pages if
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* something is sent in the current iteration.
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*/
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if (pagesize_bits > 1 && tmppages > 0) {
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migration_rate_limit();
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}
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}
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if (preempt_active) {
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qemu_mutex_lock(&rs->bitmap_mutex);
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}
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} else {
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tmppages = 0;
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}
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if (tmppages < 0) {
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return tmppages;
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}
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pss->page = migration_bitmap_find_dirty(rs, pss->block, pss->page);
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} while ((pss->page < hostpage_boundary) &&
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offset_in_ramblock(pss->block,
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