os/bluestore/compression: Main part of recompression feature

Add feature of recompression scanner that looks around write region to see how much
would be gained, if we read some more around and wrote more.
Added Compression.h / Compression.cc.
Added debug_bluestore_compression dout.
Created Scanner class.
Provides write_lookaround() for scanning loaded extents.

Signed-off-by: Adam Kupczyk <[email protected]>

Author: aclamk

src/os/bluestore/BlueStore.cc

@@ -57,6 +57,7 @@
 #include "common/WorkQueue.h"
 #include "kv/KeyValueHistogram.h"
 #include "Writer.h"
+#include "Compression.h"
 
 #if defined(WITH_LTTNG)
 #define TRACEPOINT_DEFINE
@@ -4405,6 +4406,16 @@ BlueStore::extent_map_t::iterator BlueStore::ExtentMap::maybe_split_at(uint32_t
   return p;
 }
 
+// If there exist extent at `offset` return it,
+// otherwise return smallest that `offset < logical_offset`.
+BlueStore::extent_map_t::iterator BlueStore::ExtentMap::seek_nextent(
+  uint64_t offset)
+{
+  Extent dummy(offset);
+  auto p = extent_map.lower_bound(dummy);
+  return p;
+}
+
 bool BlueStore::ExtentMap::has_any_lextents(uint64_t offset, uint64_t length)
 {
   auto fp = seek_lextent(offset);

src/os/bluestore/BlueStore.h

@@ -271,6 +271,7 @@ class BlueStore : public ObjectStore,
   struct BufferSpace;
   struct Collection;
   struct Onode;
+  class Scanner;
   class Estimator;
   typedef boost::intrusive_ptr<Collection> CollectionRef;
   typedef boost::intrusive_ptr<Onode> OnodeRef;
@@ -1171,6 +1172,8 @@ class BlueStore : public ObjectStore,
     /// seek to the first lextent including or after offset
     extent_map_t::iterator seek_lextent(uint64_t offset);
     extent_map_t::const_iterator seek_lextent(uint64_t offset) const;
+    /// seek to the exactly the extent, or after offset
+    extent_map_t::iterator seek_nextent(uint64_t offset);
 
     /// split extent
     extent_map_t::iterator split_at(extent_map_t::iterator p, uint32_t offset);