add 'release-ram' migrate capability

This feature frees the migrated memory on the source during postcopy-ram
migration. In the second step of postcopy-ram migration when the source vm
is put on pause we can free unnecessary memory. It will allow, in particular,
to start relaxing the memory stress on the source host in a load-balancing
scenario.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Message-Id: <20170203152321.19739-3-pbutsykin@virtuozzo.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
   Manually merged in Pavel's 'migration: madvise error_report fixup!'

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 7528cc2fbc82983810780e9c4fbe78ceae5d4be2..b9b706a7e31522c10c8a4a343de617cc4fea83de 100644 (file)
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -304,6 +304,7 @@ int migrate_add_blocker(Error *reason, Error **errp);
  */
 void migrate_del_blocker(Error *reason);
 
+bool migrate_release_ram(void);
 bool migrate_postcopy_ram(void);
 bool migrate_zero_blocks(void);
 

diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
index abedd466c945d4bd8a96aec519787338054a5231..0cd648a733e0a3d2b0c0d59fd2fc5215af4a191f 100644 (file)
--- a/include/migration/qemu-file.h
+++ b/include/migration/qemu-file.h
@@ -132,7 +132,8 @@ void qemu_put_byte(QEMUFile *f, int v);
  * put_buffer without copying the buffer.
  * The buffer should be available till it is sent asynchronously.
  */
-void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size);
+void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size,
+                           bool may_free);
 bool qemu_file_mode_is_not_valid(const char *mode);
 bool qemu_file_is_writable(QEMUFile *f);
 

diff --git a/migration/migration.c b/migration/migration.c
index 2b179c69fac94d23beab9b9aed9b19d349dca49c..68afc070167049c4eee27380416e9eaca287cd81 100644 (file)
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1297,6 +1297,15 @@ void qmp_migrate_set_downtime(double value, Error **errp)
     qmp_migrate_set_parameters(&p, errp);
 }
 
+bool migrate_release_ram(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_RELEASE_RAM];
+}
+
 bool migrate_postcopy_ram(void)
 {
     MigrationState *s;

diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index e9fae3115882aca356971032602304cfed580deb..195fa94fcf3e8792f4e6d8b820423924ade5eb98 100644 (file)
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -49,6 +49,7 @@ struct QEMUFile {
     int buf_size; /* 0 when writing */
     uint8_t buf[IO_BUF_SIZE];
 
+    DECLARE_BITMAP(may_free, MAX_IOV_SIZE);
     struct iovec iov[MAX_IOV_SIZE];
     unsigned int iovcnt;
 
@@ -132,6 +133,41 @@ bool qemu_file_is_writable(QEMUFile *f)
     return f->ops->writev_buffer;
 }
 
+static void qemu_iovec_release_ram(QEMUFile *f)
+{
+    struct iovec iov;
+    unsigned long idx;
+
+    /* Find and release all the contiguous memory ranges marked as may_free. */
+    idx = find_next_bit(f->may_free, f->iovcnt, 0);
+    if (idx >= f->iovcnt) {
+        return;
+    }
+    iov = f->iov[idx];
+
+    /* The madvise() in the loop is called for iov within a continuous range and
+     * then reinitialize the iov. And in the end, madvise() is called for the
+     * last iov.
+     */
+    while ((idx = find_next_bit(f->may_free, f->iovcnt, idx + 1)) < f->iovcnt) {
+        /* check for adjacent buffer and coalesce them */
+        if (iov.iov_base + iov.iov_len == f->iov[idx].iov_base) {
+            iov.iov_len += f->iov[idx].iov_len;
+            continue;
+        }
+        if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
+            error_report("migrate: madvise DONTNEED failed %p %zd: %s",
+                         iov.iov_base, iov.iov_len, strerror(errno));
+        }
+        iov = f->iov[idx];
+    }
+    if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
+            error_report("migrate: madvise DONTNEED failed %p %zd: %s",
+                         iov.iov_base, iov.iov_len, strerror(errno));
+    }
+    memset(f->may_free, 0, sizeof(f->may_free));
+}
+
 /**
  * Flushes QEMUFile buffer
  *
@@ -151,6 +187,8 @@ void qemu_fflush(QEMUFile *f)
     if (f->iovcnt > 0) {
         expect = iov_size(f->iov, f->iovcnt);
         ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos);
+
+        qemu_iovec_release_ram(f);
     }
 
     if (ret >= 0) {
@@ -304,13 +342,19 @@ int qemu_fclose(QEMUFile *f)
     return ret;
 }
 
-static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size)
+static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size,
+                         bool may_free)
 {
     /* check for adjacent buffer and coalesce them */
     if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base +
-        f->iov[f->iovcnt - 1].iov_len) {
+        f->iov[f->iovcnt - 1].iov_len &&
+        may_free == test_bit(f->iovcnt - 1, f->may_free))
+    {
         f->iov[f->iovcnt - 1].iov_len += size;
     } else {
+        if (may_free) {
+            set_bit(f->iovcnt, f->may_free);
+        }
         f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
         f->iov[f->iovcnt++].iov_len = size;
     }
@@ -320,14 +364,15 @@ static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size)
     }
 }
 
-void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size)
+void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size,
+                           bool may_free)
 {
     if (f->last_error) {
         return;
     }
 
     f->bytes_xfer += size;
-    add_to_iovec(f, buf, size);
+    add_to_iovec(f, buf, size, may_free);
 }
 
 void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size)
@@ -345,7 +390,7 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size)
         }
         memcpy(f->buf + f->buf_index, buf, l);
         f->bytes_xfer += l;
-        add_to_iovec(f, f->buf + f->buf_index, l);
+        add_to_iovec(f, f->buf + f->buf_index, l, false);
         f->buf_index += l;
         if (f->buf_index == IO_BUF_SIZE) {
             qemu_fflush(f);
@@ -366,7 +411,7 @@ void qemu_put_byte(QEMUFile *f, int v)
 
     f->buf[f->buf_index] = v;
     f->bytes_xfer++;
-    add_to_iovec(f, f->buf + f->buf_index, 1);
+    add_to_iovec(f, f->buf + f->buf_index, 1, false);
     f->buf_index++;
     if (f->buf_index == IO_BUF_SIZE) {
         qemu_fflush(f);
@@ -647,7 +692,7 @@ ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
     }
     qemu_put_be32(f, blen);
     if (f->ops->writev_buffer) {
-        add_to_iovec(f, f->buf + f->buf_index, blen);
+        add_to_iovec(f, f->buf + f->buf_index, blen, false);
     }
     f->buf_index += blen;
     if (f->buf_index == IO_BUF_SIZE) {

diff --git a/migration/ram.c b/migration/ram.c
index 91443b39617a5244d4fbdd25237b1d213a415b8e..c22209db30545b98a559180085426b359ad5f21c 100644 (file)
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -705,6 +705,16 @@ static int save_zero_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset,
     return pages;
 }
 
+static void ram_release_pages(MigrationState *ms, const char *block_name,
+                              uint64_t offset, int pages)
+{
+    if (!migrate_release_ram() || !migration_in_postcopy(ms)) {
+        return;
+    }
+
+    ram_discard_range(NULL, block_name, offset, pages << TARGET_PAGE_BITS);
+}
+
 /**
  * ram_save_page: Send the given page to the stream
  *
@@ -765,6 +775,7 @@ static int ram_save_page(MigrationState *ms, QEMUFile *f, PageSearchStatus *pss,
              * page would be stale
              */
             xbzrle_cache_zero_page(current_addr);
+            ram_release_pages(ms, block->idstr, pss->offset, pages);
         } else if (!ram_bulk_stage &&
                    !migration_in_postcopy(ms) && migrate_use_xbzrle()) {
             pages = save_xbzrle_page(f, &p, current_addr, block,
@@ -783,7 +794,9 @@ static int ram_save_page(MigrationState *ms, QEMUFile *f, PageSearchStatus *pss,
         *bytes_transferred += save_page_header(f, block,
                                                offset | RAM_SAVE_FLAG_PAGE);
         if (send_async) {
-            qemu_put_buffer_async(f, p, TARGET_PAGE_SIZE);
+            qemu_put_buffer_async(f, p, TARGET_PAGE_SIZE,
+                                  migrate_release_ram() &
+                                  migration_in_postcopy(ms));
         } else {
             qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
         }
@@ -813,6 +826,8 @@ static int do_compress_ram_page(QEMUFile *f, RAMBlock *block,
         error_report("compressed data failed!");
     } else {
         bytes_sent += blen;
+        ram_release_pages(migrate_get_current(), block->idstr,
+                          offset & TARGET_PAGE_MASK, 1);
     }
 
     return bytes_sent;
@@ -952,12 +967,17 @@ static int ram_save_compressed_page(MigrationState *ms, QEMUFile *f,
                     error_report("compressed data failed!");
                 }
             }
+            if (pages > 0) {
+                ram_release_pages(ms, block->idstr, pss->offset, pages);
+            }
         } else {
             offset |= RAM_SAVE_FLAG_CONTINUE;
             pages = save_zero_page(f, block, offset, p, bytes_transferred);
             if (pages == -1) {
                 pages = compress_page_with_multi_thread(f, block, offset,
                                                         bytes_transferred);
+            } else {
+                ram_release_pages(ms, block->idstr, pss->offset, pages);
             }
         }
     }

diff --git a/qapi-schema.json b/qapi-schema.json
index 61151f34d0cfff3d653782d775ae1e153fb07b7f..93305412dd47f0dd5000721b3610b67c193dcd95 100644 (file)
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -865,11 +865,14 @@
 #        side, this process is called COarse-Grain LOck Stepping (COLO) for
 #        Non-stop Service. (since 2.8)
 #
+# @release-ram: if enabled, qemu will free the migrated ram pages on the source
+#        during postcopy-ram migration. (since 2.9)
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
   'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
-           'compress', 'events', 'postcopy-ram', 'x-colo'] }
+           'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram'] }
 
 ##
 # @MigrationCapabilityStatus: