Revert "page_cache: find_victim: don't spin while there's no chance f…

…or a slot (#5319)"

To repro the original condition.

This reverts commit c07eef8.

pageserver/src/metrics.rs

@@ -264,46 +264,6 @@ pub static PAGE_CACHE_SIZE: Lazy<PageCacheSizeMetrics> = Lazy::new(|| PageCacheS
     },
 });
 
-pub(crate) static PAGE_CACHE_ACQUIRE_PINNED_SLOT_TIME: Lazy<Histogram> = Lazy::new(|| {
-    register_histogram!(
-        "pageserver_page_cache_acquire_pinned_slot_seconds",
-        "Time spent acquiring a pinned slot in the page cache",
-        CRITICAL_OP_BUCKETS.into(),
-    )
-    .expect("failed to define a metric")
-});
-
-pub(crate) static PAGE_CACHE_FIND_VICTIMS_ITERS_TOTAL: Lazy<IntCounter> = Lazy::new(|| {
-    register_int_counter!(
-        "pageserver_page_cache_find_victim_iters_total",
-        "Counter for the number of iterations in the find_victim loop",
-    )
-    .expect("failed to define a metric")
-});
-
-static PAGE_CACHE_ERRORS: Lazy<IntCounterVec> = Lazy::new(|| {
-    register_int_counter_vec!(
-        "page_cache_errors_total",
-        "Number of timeouts while acquiring a pinned slot in the page cache",
-        &["error_kind"]
-    )
-    .expect("failed to define a metric")
-});
-
-#[derive(IntoStaticStr)]
-#[strum(serialize_all = "kebab_case")]
-pub(crate) enum PageCacheErrorKind {
-    AcquirePinnedSlotTimeout,
-    EvictIterLimit,
-}
-
-pub(crate) fn page_cache_errors_inc(error_kind: PageCacheErrorKind) {
-    PAGE_CACHE_ERRORS
-        .get_metric_with_label_values(&[error_kind.into()])
-        .unwrap()
-        .inc();
-}
-
 pub(crate) static WAIT_LSN_TIME: Lazy<Histogram> = Lazy::new(|| {
     register_histogram!(
         "pageserver_wait_lsn_seconds",