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authorDavid Hildenbrand <david@redhat.com>2021-07-27 10:25:45 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2021-10-02 08:43:22 +0200
commitcb83ba8c1ab856b4327e7e869c410bbfd4152c2c (patch)
treea02a3db34ecb823eefc2b97caed98bda990f74bc /softmmu
parent3513bb1be1f025e011a69bafd02b6f59fa1d8383 (diff)
softmmu/memory_mapping: optimize for RamDiscardManager sections
virtio-mem logically plugs/unplugs memory within a sparse memory region and notifies via the RamDiscardManager interface when parts become plugged (populated) or unplugged (discarded). Currently, we end up (via the two users) 1) zeroing all logically unplugged/discarded memory during TPM resets. 2) reading all logically unplugged/discarded memory when dumping, to figure out the content is zero. 1) is always bad, because we assume unplugged memory stays discarded (and is already implicitly zero). 2) isn't that bad with anonymous memory, we end up reading the zero page (slow and unnecessary, though). However, once we use some file-backed memory (future use case), even reading will populate memory. Let's cut out all parts marked as not-populated (discarded) via the RamDiscardManager. As virtio-mem is the single user, this now means that logically unplugged memory ranges will no longer be included in the dump, which results in smaller dump files and faster dumping. virtio-mem has a minimum granularity of 1 MiB (and the default is usually 2 MiB). Theoretically, we can see quite some fragmentation, in practice we won't have it completely fragmented in 1 MiB pieces. Still, we might end up with many physical ranges. Both, the ELF format and kdump seem to be ready to support many individual ranges (e.g., for ELF it seems to be UINT32_MAX, kdump has a linear bitmap). Reviewed-by: Peter Xu <peterx@redhat.com> Cc: Marc-André Lureau <marcandre.lureau@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Eduardo Habkost <ehabkost@redhat.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com> Cc: Igor Mammedov <imammedo@redhat.com> Cc: Claudio Fontana <cfontana@suse.de> Cc: Thomas Huth <thuth@redhat.com> Cc: "Alex Bennée" <alex.bennee@linaro.org> Cc: Peter Xu <peterx@redhat.com> Cc: Laurent Vivier <lvivier@redhat.com> Cc: Stefan Berger <stefanb@linux.ibm.com> Signed-off-by: David Hildenbrand <david@redhat.com> Message-Id: <20210727082545.17934-5-david@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'softmmu')
-rw-r--r--softmmu/memory_mapping.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/softmmu/memory_mapping.c b/softmmu/memory_mapping.c
index a2af02c41c..a62eaa49cc 100644
--- a/softmmu/memory_mapping.c
+++ b/softmmu/memory_mapping.c
@@ -246,6 +246,15 @@ static void guest_phys_block_add_section(GuestPhysListener *g,
#endif
}
+static int guest_phys_ram_populate_cb(MemoryRegionSection *section,
+ void *opaque)
+{
+ GuestPhysListener *g = opaque;
+
+ guest_phys_block_add_section(g, section);
+ return 0;
+}
+
static void guest_phys_blocks_region_add(MemoryListener *listener,
MemoryRegionSection *section)
{
@@ -257,6 +266,17 @@ static void guest_phys_blocks_region_add(MemoryListener *listener,
memory_region_is_nonvolatile(section->mr)) {
return;
}
+
+ /* for special sparse regions, only add populated parts */
+ if (memory_region_has_ram_discard_manager(section->mr)) {
+ RamDiscardManager *rdm;
+
+ rdm = memory_region_get_ram_discard_manager(section->mr);
+ ram_discard_manager_replay_populated(rdm, section,
+ guest_phys_ram_populate_cb, g);
+ return;
+ }
+
guest_phys_block_add_section(g, section);
}