Re: [libvirt] [PATCH v4 5/5] qemu: Introduce memoryBacking/discard

https://bugzilla.redhat.com/show_bug.cgi?id=1480668 QEMU has this new feature memory-backend-file.discard-data=yes which is a nifty optimization. Basically, when qemu is quitting or on memory hotplug it calls munmap() and close() on the file that is backing the memory. However, this does not mean kernel won't stop touching that part of memory. It still might. With this feature enabled we tell kernel: "we don't need this memory nor data stored in it". This makes kernel drop the memory immediately without trying to sync memory with the mapped file. Unfortunately, this cannot be turned on by default because we can't be sure when users really don't care about what happens to data after qemu dies. So it has to be opt-in. As usual, there are three places where one can configure memory attributes. This patch adds the feature to all of them.

Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- docs/formatdomain.html.in | 34 ++++++++++++++++++++++-- docs/schemas/cputypes.rng | 5 ++++ docs/schemas/domaincommon.rng | 10 +++++++ src/conf/domain_conf.c | 39 ++++++++++++++++++++++++++-- src/conf/domain_conf.h | 3 +++ src/conf/numa_conf.c | 27 +++++++++++++++++++ src/conf/numa_conf.h | 3 +++ src/libvirt_private.syms | 1 + src/qemu/qemu_command.c | 27 ++++++++++++++++--- tests/qemuxml2argvdata/hugepages-pages7.args | 3 ++- tests/qemuxml2argvdata/hugepages-pages7.xml | 4 +-- tests/qemuxml2argvtest.c | 3 ++- 12 files changed, 148 insertions(+), 11 deletions(-)

@@ -26658,7 +26690,8 @@ virDomainDefFormatInternal(virDomainDefPtr def, }

if (def->mem.nhugepages || def->mem.nosharepages || def->mem.locked - || def->mem.source || def->mem.access || def->mem.allocation) + || def->mem.source || def->mem.access || def->mem.allocation + || def->mem.discard)

{ virBufferAddLit(buf, "<memoryBacking>\n"); virBufferAdjustIndent(buf, 2); @@ -26677,6 +26710,8 @@ virDomainDefFormatInternal(virDomainDefPtr def, if (def->mem.allocation) virBufferAsprintf(buf, "<allocation mode='%s'/>\n", virDomainMemoryAllocationTypeToString(def->mem.allocation)); + if (def->mem.discard) + virBufferAddLit(buf, "<discard/>\n"); virBufferAdjustIndent(buf, -2); virBufferAddLit(buf, "</memoryBacking>\n"); diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h index 3c7eccb8ca..52d29124f1 100644 --- a/src/conf/domain_conf.h +++ b/src/conf/domain_conf.h @@ -2107,6 +2107,7 @@ typedef enum { struct _virDomainMemoryDef { virDomainMemoryAccess access; + int discard; /* enum virTristateBool */

/* source */ virBitmapPtr sourceNodes; @@ -2269,6 +2270,8 @@ struct _virDomainMemtune { int source; /* enum virDomainMemorySource */ int access; /* enum virDomainMemoryAccess */ int allocation; /* enum virDomainMemoryAllocation */ + + int discard; /* enum virTristateBool */

}; typedef struct _virDomainPowerManagement virDomainPowerManagement; diff --git a/src/conf/numa_conf.c b/src/conf/numa_conf.c index 9307dd93d3..a1bbcfa945 100644 --- a/src/conf/numa_conf.c +++ b/src/conf/numa_conf.c @@ -77,6 +77,7 @@ struct _virDomainNuma { virBitmapPtr nodeset; /* host memory nodes where this guest node resides */ virDomainNumatuneMemMode mode; /* memory mode selection */ virDomainMemoryAccess memAccess; /* shared memory access configuration */ + int discard; /* discard-data for memory-backend-file, virTristateBool */

struct _virDomainNumaDistance { unsigned int value; /* locality value for node i->j or j->i */