MDEV-36587 InnoDB uses too much memory

log_t::clear_mmap(): Do not modify buf_size; we may have
file_size==0 here during bootstrap.

log_t::set_recovered(): If we are writing to a memory-mapped log,
update log_sys.buf_size to the record payload area of log_sys.buf.

This fixes up commit acd071f
(MDEV-21923).

Author: dr-m

storage/innobase/log/log0log.cc

@@ -1237,11 +1237,10 @@ void log_t::clear_mmap() noexcept
 #ifdef HAVE_PMEM
   if (!is_opened())
   {
-    latch.wr_lock(SRW_LOCK_CALL);
+    ut_d(latch.wr_lock(SRW_LOCK_CALL));
     ut_ad(!resize_in_progress());
     ut_ad(get_lsn() == get_flushed_lsn(std::memory_order_relaxed));
-    buf_size= unsigned(std::min<uint64_t>(capacity(), buf_size_max));
-    latch.wr_unlock();
+    ut_d(latch.wr_unlock());
     return;
   }
 #endif

storage/innobase/log/log0recv.cc

@@ -4590,7 +4590,10 @@ inline void log_t::set_recovered() noexcept
   }
 #ifdef HAVE_PMEM
   else
+  {
+    buf_size= unsigned(std::min<uint64_t>(capacity(), buf_size_max));
     mprotect(buf, size_t(file_size), PROT_READ | PROT_WRITE);
+  }
 #endif
 }