[WIP] Use fetch_max instead of bump_atomic_lsn

SAFETY.md

@@ -95,6 +95,7 @@ durability model
       * return None if last_lsn_in_batch >= self.max_lsn
     * batch requirement set to last reservation base + inline len - 1
       * reserve bumps
+	  	* TODO: Change this
         * bump_atomic_lsn(&self.iobufs.max_reserved_lsn, reservation_lsn + inline_buf_len as Lsn - 1);
 
 lock-free linearizability model

src/pagecache/iobuf.rs

@@ -825,7 +825,7 @@ impl IoBufs {
         let max_header_stable_lsn = self.max_header_stable_lsn.clone();
         guard.defer(move || {
             trace!("bumping atomic header lsn to {}", stored_max_stable_lsn);
-            bump_atomic_lsn(&max_header_stable_lsn, stored_max_stable_lsn)
+            AtomicLsn::fetch_max(&max_header_stable_lsn, stored_max_stable_lsn, SeqCst)
         });
 
         guard.flush();

src/pagecache/logger.rs

@@ -1,7 +1,7 @@
 use std::fs::File;
 
 use super::{
-    arr_to_lsn, arr_to_u32, assert_usize, bump_atomic_lsn, decompress, header,
+    arr_to_lsn, arr_to_u32, assert_usize, decompress, header,
     iobuf, lsn_to_arr, pread_exact, pread_exact_or_eof, roll_iobuf, u32_to_arr,
     Arc, BasedBuf, DiskPtr, HeapId, IoBuf, IoBufs, LogKind, LogOffset, Lsn,
     MessageKind, Reservation, Serialize, Snapshot, BATCH_MANIFEST_PID,
@@ -364,9 +364,10 @@ impl Log {
                 reservation_lid,
             );
 
-            bump_atomic_lsn(
+            AtomicLsn::fetch_max(
                 &self.iobufs.max_reserved_lsn,
                 reservation_lsn + inline_buf_len as Lsn - 1,
+                SeqCst
             );
 
             let (heap_reservation, heap_id) = if over_heap_threshold {

src/pagecache/mod.rs

@@ -206,22 +206,6 @@ where
     usize::try_from(from).expect("lost data cast while converting to usize")
 }
 
-// TODO remove this when atomic fetch_max stabilizes in #48655
-fn bump_atomic_lsn(atomic_lsn: &AtomicLsn, to: Lsn) {
-    let mut current = atomic_lsn.load(Acquire);
-    loop {
-        if current >= to {
-            return;
-        }
-        let last = atomic_lsn.compare_and_swap(current, to, SeqCst);
-        if last == current {
-            // we succeeded.
-            return;
-        }
-        current = last;
-    }
-}
-
 use std::convert::{TryFrom, TryInto};
 
 #[inline]
@@ -992,7 +976,7 @@ impl PageCache {
         snapshot::write_snapshot(&self.config, &snapshot)?;
 
         // NB: this must only happen after writing the snapshot to disk
-        bump_atomic_lsn(&self.snapshot_min_lsn, stable_lsn_before);
+        AtomicLsn::fetch_max(&self.snapshot_min_lsn, stable_lsn_before, SeqCst);
 
         // explicitly drop this to make it clear that it needs to
         // be held for the duration of the snapshot operation.