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AKwUvBxQTzw/TzIMT7BzbTbTVBloFDP7fEc9aIKdvnlZC3lgc1wyzvqgln5hwSEcjwWgqHb2QlGUrQx747x0jMc=@vger.kernel.org X-Gm-Message-State: APuU4Z9nEap4tZcPP3lQBGxkhQKAbkrZqJwm9hNW5jhe43+MmusVmFqm M0f+aGBw9sk22/c7kKOneR+pmzS2EJG5BjgZeUXPtOalodp4/S6Mu6bg5HiEOwLwWbWZi6YlUm6 PbVdUyW3dV0RjXVfl+EH+3g== X-Received: from dldyr25-n2.prod.google.com ([2002:a05:701b:4519:20b0:195:cde8:ab41]) (user=robertpang job=prod-delivery.src-stubby-dispatcher) by 2002:a05:7022:1089:b0:14d:3c0c:79e9 with SMTP id a92af1059eb24-1ac5b027fccmr17755954c88.11.1793689460359; Mon, 02 Nov 2026 23:04:20 -0800 (PST) Date: Mon, 2 Nov 2026 23:04:06 -0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 X-Mailer: git-send-email 2.56.0.398.g882cbad275-goog Message-ID: <20261103070407.1211071-1-robertpang@google.com> Subject: [PATCH] bcache: fix available bucket accounting in bucket allocation From: Robert Pang To: colyli@fygo.io, kent.overstreet@linux.dev Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, robertpang@google.com Content-Type: text/plain; charset="UTF-8" In bch_bucket_alloc(), a cache set's avail_nbuckets is decremented whenever a bucket is allocated, assuming that the bucket becomes unavailable once allocated. However, when a bucket is allocated but the GC mark is unset or reclaimable, it is available still. This false counter decrement leads to an inflated in-use measurement, which triggers cache bypasses once CUTOFF_CACHE_ADD is reached, persisting until the next garbage collection cycle. Fix this by ensuring avail_nbuckets is only decremented when the allocated bucket is already marked and not in the GC_MARK_RECLAIMABLE state. Signed-off-by: Robert Pang --- drivers/md/bcache/alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c index 3ec240ec685d..2d0cb9b414ac 100644 --- a/drivers/md/bcache/alloc.c +++ b/drivers/md/bcache/alloc.c @@ -446,7 +446,8 @@ long bch_bucket_alloc(struct cache *ca, unsigned int reserve, bool wait) b->prio = INITIAL_PRIO; } - if (ca->set->avail_nbuckets > 0) { + if (ca->set->avail_nbuckets > 0 && + GC_MARK(b) && GC_MARK(b) != GC_MARK_RECLAIMABLE) { ca->set->avail_nbuckets--; bch_update_bucket_in_use(ca->set, &ca->set->gc_stats); } -- 2.56.0.398.g882cbad275-goog