From c7ce813fe49a58344ba11219c0bd3a2fdb2e8b9e Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Mon, 27 Dec 2021 20:45:07 -0500 Subject: [PATCH] bcachefs: Add a tracepoint for the btree cache shrinker This is to help with diagnosing why the btree node can doesn't seem to be shrinking - we've had issues in the past with granularity/batch size, since btree nodes are so big. Signed-off-by: Kent Overstreet --- fs/bcachefs/btree_cache.c | 11 +++++++++-- fs/bcachefs/trace.h | 28 ++++++++++++++++++++++++++++ 2 files changed, 37 insertions(+), 2 deletions(-) diff --git a/fs/bcachefs/btree_cache.c b/fs/bcachefs/btree_cache.c index 5bf493a315caf..40061887f5d88 100644 --- a/fs/bcachefs/btree_cache.c +++ b/fs/bcachefs/btree_cache.c @@ -275,6 +275,7 @@ static unsigned long bch2_btree_cache_scan(struct shrinker *shrink, unsigned long touched = 0; unsigned long freed = 0; unsigned i, flags; + unsigned long ret = SHRINK_STOP; if (bch2_btree_shrinker_disabled) return SHRINK_STOP; @@ -283,7 +284,7 @@ static unsigned long bch2_btree_cache_scan(struct shrinker *shrink, if (sc->gfp_mask & __GFP_FS) mutex_lock(&bc->lock); else if (!mutex_trylock(&bc->lock)) - return -1; + goto out_norestore; flags = memalloc_nofs_save(); @@ -358,8 +359,14 @@ restart: mutex_unlock(&bc->lock); out: + ret = (unsigned long) freed * btree_pages(c); memalloc_nofs_restore(flags); - return (unsigned long) freed * btree_pages(c); +out_norestore: + trace_btree_cache_scan(sc->nr_to_scan, + sc->nr_to_scan / btree_pages(c), + btree_cache_can_free(bc), + ret); + return ret; } static unsigned long bch2_btree_cache_count(struct shrinker *shrink, diff --git a/fs/bcachefs/trace.h b/fs/bcachefs/trace.h index 21d026277540f..a1122fa3ccc6b 100644 --- a/fs/bcachefs/trace.h +++ b/fs/bcachefs/trace.h @@ -318,6 +318,34 @@ DEFINE_EVENT(btree_node, btree_set_root, TP_ARGS(c, b) ); +TRACE_EVENT(btree_cache_scan, + TP_PROTO(unsigned long nr_to_scan_pages, + unsigned long nr_to_scan_nodes, + unsigned long can_free_nodes, + long ret), + TP_ARGS(nr_to_scan_pages, nr_to_scan_nodes, can_free_nodes, ret), + + TP_STRUCT__entry( + __field(unsigned long, nr_to_scan_pages ) + __field(unsigned long, nr_to_scan_nodes ) + __field(unsigned long, can_free_nodes ) + __field(long, ret ) + ), + + TP_fast_assign( + __entry->nr_to_scan_pages = nr_to_scan_pages; + __entry->nr_to_scan_nodes = nr_to_scan_nodes; + __entry->can_free_nodes = can_free_nodes; + __entry->ret = ret; + ), + + TP_printk("scanned for %lu pages, %lu nodes, can free %lu nodes, ret %li", + __entry->nr_to_scan_pages, + __entry->nr_to_scan_nodes, + __entry->can_free_nodes, + __entry->ret) +); + /* Garbage collection */ DEFINE_EVENT(btree_node, btree_gc_rewrite_node, -- 2.30.2