MDEV-33585 follow-up optimization

log_t: Define buf_size, max_buf_free as 32-bit and next_checkpoint_no
as byte (we only need a bit) and rearrange some data members,
so that on AMD64 we can fit log_sys.latch and log_sys.log in
the same 64-byte cache line.

mtr_t::commit_log(), mtr_t::commit_logger: A part of mtr_t::commit()
split into a separate function, so that we will not unnecessarily invoke
log_sys.get_write_target() when running on a memory-mapped log file,
or log_sys.is_pmem().

Reviewed by: Vladislav Vaintroub
Tested by: Matthias Leich

storage/innobase/include/log0log.h

@@ -230,8 +230,6 @@ struct log_t
 
   /** Last written LSN */
   lsn_t write_lsn;
-  /** recommended maximum buf_free size, after which the buffer is flushed */
-  size_t max_buf_free;
 
   /** buffer for writing data to ib_logfile0, or nullptr if is_pmem()
   In write_buf(), buf and flush_buf are swapped */
@@ -241,6 +239,10 @@ struct log_t
   std::atomic<bool> need_checkpoint;
   /** whether a checkpoint is pending; protected by latch.wr_lock() */
   Atomic_relaxed<bool> checkpoint_pending;
+  /** next checkpoint number (protected by latch.wr_lock()) */
+  byte next_checkpoint_no;
+  /** recommended maximum buf_free size, after which the buffer is flushed */
+  unsigned max_buf_free;
   /** Log sequence number when a log file overwrite (broken crash recovery)
   was noticed. Protected by latch.wr_lock(). */
   lsn_t overwrite_warned;
@@ -249,8 +251,6 @@ struct log_t
   Atomic_relaxed<lsn_t> last_checkpoint_lsn;
   /** next checkpoint LSN (protected by latch.wr_lock()) */
   lsn_t next_checkpoint_lsn;
-  /** next checkpoint number (protected by latch.wr_lock()) */
-  ulint next_checkpoint_no;
 
   /** Log file */
   log_file_t log;
@@ -323,6 +323,7 @@ struct log_t
   /** whether there is capacity in the log buffer */
   bool buf_free_ok() const noexcept
   {
+    ut_ad(!is_pmem());
     return (buf_free.load(std::memory_order_relaxed) & ~buf_free_LOCK) <
       max_buf_free;
   }

storage/innobase/include/mtr0mtr.h

@@ -695,6 +695,13 @@ struct mtr_t {
   /** Encrypt the log */
   ATTRIBUTE_NOINLINE void encrypt();
 
+  /** Commit the mini-transaction log.
+  @tparam pmem log_sys.is_pmem()
+  @param mtr   mini-transaction
+  @param lsns  {start_lsn,flush_ahead} */
+  template<bool pmem>
+  static void commit_log(mtr_t *mtr, std::pair<lsn_t,page_flush_ahead> lsns);
+
   /** Append the redo log records to the redo log buffer.
   @return {start_lsn,flush_ahead} */
   std::pair<lsn_t,page_flush_ahead> do_write();
@@ -708,6 +715,8 @@ struct mtr_t {
   template<bool spin,bool pmem> static
   std::pair<lsn_t,page_flush_ahead> finish_writer(mtr_t *mtr, size_t len);
 
+  /** The applicable variant of commit_log() */
+  static void (*commit_logger)(mtr_t *, std::pair<lsn_t,page_flush_ahead>);
   /** The applicable variant of finish_writer() */
   static std::pair<lsn_t,page_flush_ahead> (*finisher)(mtr_t *, size_t);
 

storage/innobase/log/log0log.cc

@@ -235,7 +235,7 @@ void log_t::attach_low(log_file_t file, os_offset_t size)
       log.close();
       mprotect(ptr, size_t(size), PROT_READ);
       buf= static_cast<byte*>(ptr);
-      max_buf_free= size;
+      max_buf_free= 1;
 # if defined __linux__ || defined _WIN32
       set_block_size(CPU_LEVEL1_DCACHE_LINESIZE);
 # endif