Merge pull request ceph#62224 from aclamk/wip-aclamk-pere-wal-fsync

os/bluestore: Fast WAL for RocksDB

Author: aclamk

doc/man/8/ceph-bluestore-tool.rst

@@ -34,6 +34,7 @@ Synopsis
 | **ceph-bluestore-tool** show-sharding --path *osd path*
 | **ceph-bluestore-tool** trim --path *osd path*
 | **ceph-bluestore-tool** zap-device --dev *dev path*
+| **ceph-bluestore-tool** revert-wal-to-plain --path *osd path*
 
 
 Description
@@ -165,6 +166,11 @@ Commands
 
    Zeros all device label locations. This effectively makes device appear empty.
 
+:command: `revert-wal-to-plain` --path *osd path*
+
+   Changes WAL files from envelope mode to the legacy plain mode.
+   Useful for downgrades, or if you might want to disable this new feature (bluefs_wal_envelope_mode).
+
 Options
 =======
 

src/common/options/global.yaml.in

@@ -4248,6 +4248,15 @@ options:
   level: advanced
   default: false
   with_legacy: true
+- name: bluefs_wal_envelope_mode
+  type: bool
+  level: advanced
+  desc: Enables a faster backend in BlueFS for WAL writes.
+  long_desc: In envelope mode BlueFS files do not need to update metadata. When applied to RocksDB WAL files,
+    it reduces by ~50% the amount of fdatasync syscalls.
+    Downgrading from an envelope mode to legacy mode requires `ceph-bluestore-tool --command downgrade-wal-to-v1`.
+  default: true
+  with_legacy: false
 - name: bluefs_allocator
   type: str
   level: dev

src/include/buffer.h

@@ -834,6 +834,7 @@ struct error_code;
       contiguous_filler(char* const pos) : pos(pos) {}
 
     public:
+      contiguous_filler() : pos(nullptr) {}
       void advance(const unsigned len) {
 	pos += len;
       }

src/include/denc.h

@@ -1835,8 +1835,6 @@ struct StructVChecker
     p += 2 + 4;								\
   }									\
   static void _denc_finish(size_t& p,					\
-			   __u8 *struct_v,				\
-			   __u8 *struct_compat,				\
 			   char **, uint32_t *) { }			\
   /* encode */								\
   static void _denc_start(::ceph::buffer::list::contiguous_appender& p,	\
@@ -1850,8 +1848,6 @@ struct StructVChecker
     *start_oob_off = p.get_out_of_band_offset();			\
   }									\
   static void _denc_finish(::ceph::buffer::list::contiguous_appender& p, \
-			   __u8 *struct_v,				\
-			   __u8 *struct_compat,				\
 			   char **len_pos,				\
 			   uint32_t *start_oob_off) {			\
     *(ceph_le32*)*len_pos = p.get_pos() - *len_pos - sizeof(uint32_t) +	\
@@ -1872,7 +1868,6 @@ struct StructVChecker
     *start_pos = const_cast<char*>(p.get_pos());			\
   }									\
   static void _denc_finish(::ceph::buffer::ptr::const_iterator& p,	\
-			   __u8 *struct_v, __u8 *struct_compat,		\
 			   char **start_pos,				\
 			   uint32_t *struct_len) {			\
     const char *pos = p.get_pos();					\
@@ -1902,6 +1897,16 @@ struct StructVChecker
   _denc_start(p, &struct_v.v, &struct_compat, &_denc_pchar, &_denc_u32);	\
   do {
 
+// the variant for seldom-used cases when we manually select encoding version
+#define DENC_START_UNCHECKED(_v, compat, p)				\
+  __u8 struct_v = _v; 							\
+  __u8 struct_compat = compat;						\
+  char *_denc_pchar;							\
+  uint32_t _denc_u32;							\
+  static_assert(CEPH_RELEASE >= (CEPH_RELEASE_SQUID /*19*/ + 2) || compat == 1);	\
+  _denc_start(p, &struct_v, &struct_compat, &_denc_pchar, &_denc_u32);	\
+  do {
+
 // For the only type that is with compat 2: unittest.
 #define DENC_START_COMPAT_2(_v, compat, p)				\
   StructVChecker<_v> struct_v{_v};					\
@@ -1912,6 +1917,16 @@ struct StructVChecker
   _denc_start(p, &struct_v.v, &struct_compat, &_denc_pchar, &_denc_u32);	\
   do {
 
+// This variant is unsafe, because older versions will not even catch incompatibility.
+// The ability to decode must be verified by other means,
+#define DENC_START_UNSAFE(v, compat, p)				\
+  __u8 struct_v = v;							\
+  __u8 struct_compat = compat;						\
+  char *_denc_pchar;							\
+  uint32_t _denc_u32;							\
+  _denc_start(p, &struct_v, &struct_compat, &_denc_pchar, &_denc_u32);	\
+  do {
+
 // For osd_reqid_t which cannot be upgraded at all.
 // We used it to communicate with clients and now we cannot safely upgrade.
 #define DENC_START_OSD_REQID(_v, compat, p)				\
@@ -1925,8 +1940,7 @@ struct StructVChecker
 
 #define DENC_FINISH(p)							\
   } while (false);							\
-  _denc_finish(p, &struct_v.v, &struct_compat, &_denc_pchar, &_denc_u32);
-
+  _denc_finish(p, &_denc_pchar, &_denc_u32);
 
 // ----------------------------------------------------------------------