From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A03403002D1 for ; Wed, 10 Jun 2026 19:23:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781119391; cv=none; b=FdGtzsSXZiu2lfwgxIDPrHB+GZm4T3nTJA72BgPtDyVqkoD/Ze4/awHsG0zOjYiS/MB7UksEGqx7d4kqZMuX5GIs4yz4i53SoIlsmW5jhujLFbIRFAgrn5mQKkkc87Bn0jpWaalMiS8MPk0oeJ5Uyz++opTzrWTSzItTR6xGfGs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781119391; c=relaxed/simple; bh=NJewdxZvpJ4YYH3dhp3E3gyPK09zc/gdxzJ1PEAjB8I=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=QT/31ROp0YytGgyT3N6SEbErsjqNUZxETZup6zgAGH3drek8GmqbgLfZSxaEMBaDJRqgR9cw3Kc0chT/+zT+MqunKmR5be1x92vBkJD8HRCYjoU0u671KN0uFQHZGdYIM9zy5bE7WEfVRT3Jgb4Butwz1pVBpey/QVfB5iHTfss= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=J9HpL/4+; arc=none smtp.client-ip=91.218.175.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="J9HpL/4+" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781119226; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qWcyqlFHr5mEY42mMiFua4E/gMz+s/X2vILeDjuLg30=; b=J9HpL/4+E3jEKvbtYmDAMJUgYViuJPtNed4QFKKvOa1p4lg+r7fS6BGHUGAvB3m36bE+ek V92qDCwWhQGhPfkq24rX/i31U5boavRKK4AoX2zXj34jzt5/6YVceXVs1yx1iHuYldBGzh yu5+6uON6ZndR5c6kTbmdfg3aeshNZI= Date: Wed, 10 Jun 2026 12:20:19 -0700 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] mm/lruvec: trace LRU add drains and drain-all queuing X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: JP Kobryn To: Shakeel Butt Cc: Barry Song , linux-mm@kvack.org, willy@infradead.org, usama.arif@linux.dev, akpm@linux-foundation.org, vbabka@kernel.org, mhocko@suse.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, kasong@tencent.com, qi.zheng@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chrisl@kernel.org, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, youngjun.park@lge.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org References: <20260609041156.31127-1-jp.kobryn@linux.dev> <3e55e520-b979-4b1c-874c-3b4e5ca629e2@linux.dev> <6e7739cc-327e-4ca9-86f4-17729b624632@linux.dev> Content-Language: en-US In-Reply-To: <6e7739cc-327e-4ca9-86f4-17729b624632@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 6/10/26 11:54 AM, JP Kobryn wrote: > On 6/9/26 6:21 PM, Shakeel Butt wrote: >> On Tue, Jun 09, 2026 at 05:16:15PM -0700, JP Kobryn wrote: >>> On 6/9/26 5:07 PM, JP Kobryn wrote: >>>> On 6/9/26 12:44 AM, Barry Song wrote: >>>>> On Tue, Jun 9, 2026 at 12:12 PM JP Kobryn wrote: >>>>>> >>>>>> LRU add batches can be drained before they reach capacity. This can be a >>>>>> source of LRU lock contention, but it is not currently possible to >>>>>> attribute these drains to callers with existing tracepoints. >>>>>> >>>>>> Add mm_lru_add_drain to report the CPU and lru_add batch count when an >>>>>> lru_add batch is drained. This allows tracing to distinguish full drains >>>>>> from partial drains and attribute them to the calling stack. >>>>>> >>>>>> Add mm_lru_drain_all_queue to report when lru_add_drain_all() queues >>>>>> per-CPU drain work. This captures the requester stack and target CPU for >>>>>> remote drain work. The event is named as a drain-all queue event because >>>>>> the queued work can be needed for batches other than lru_add. >>>>>> >>>>>> Signed-off-by: JP Kobryn >>>>>> --- >>>>>> include/trace/events/pagemap.h | 40 ++++++++++++++++++++++++++++++++++ >>>>>> mm/swap.c | 6 ++++- >>>>>> 2 files changed, 45 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h >>>>>> index 171524d3526d..ea8fc46bedb0 100644 >>>>>> --- a/include/trace/events/pagemap.h >>>>>> +++ b/include/trace/events/pagemap.h >>>>>> @@ -77,6 +77,46 @@ TRACE_EVENT(mm_lru_activate, >>>>>> TP_printk("folio=%p pfn=0x%lx", __entry->folio, __entry->pfn) >>>>>> ); >>>>>> >>>>>> +TRACE_EVENT(mm_lru_add_drain, >>>>>> + >>>>>> + TP_PROTO(int cpu, unsigned int nr), >>>>>> + >>>>>> + TP_ARGS(cpu, nr), >>>>>> + >>>>>> + TP_STRUCT__entry( >>>>>> + __field(int, cpu ) >>>>>> + __field(unsigned int, nr ) >>>>>> + ), >>>>>> + >>>>>> + TP_fast_assign( >>>>>> + __entry->cpu = cpu; >>>>>> + __entry->nr = nr; >>>>>> + ), >>>>>> + >>>>>> + TP_printk("cpu=%d nr=%u", __entry->cpu, __entry->nr) >>>>>> +); >>>>>> + >>>>>> +TRACE_EVENT(mm_lru_drain_all_queue, >>>>>> + >>>>>> + TP_PROTO(int target_cpu, bool force_all_cpus), >>>>>> + >>>>>> + TP_ARGS(target_cpu, force_all_cpus), >>>>>> + >>>>>> + TP_STRUCT__entry( >>>>>> + __field(int, target_cpu ) >>>>>> + __field(bool, force_all_cpus ) >>>>>> + ), >>>>>> + >>>>>> + TP_fast_assign( >>>>>> + __entry->target_cpu = target_cpu; >>>>>> + __entry->force_all_cpus = force_all_cpus; >>>>>> + ), >>>>>> + >>>>>> + TP_printk("target_cpu=%d force_all_cpus=%s", >>>>>> + __entry->target_cpu, >>>>>> + __entry->force_all_cpus ? "true" : "false") >>>>>> +); >>>>>> + >>>>>> #endif /* _TRACE_PAGEMAP_H */ >>>>>> >>>>>> /* This part must be outside protection */ >>>>>> diff --git a/mm/swap.c b/mm/swap.c >>>>>> index 588f50d8f1a8..c385b93582eb 100644 >>>>>> --- a/mm/swap.c >>>>>> +++ b/mm/swap.c >>>>>> @@ -694,9 +694,12 @@ void lru_add_drain_cpu(int cpu) >>>>>> { >>>>>> struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu); >>>>>> struct folio_batch *fbatch = &fbatches->lru_add; >>>>>> + unsigned int nr_folios_add = folio_batch_count(fbatch); >>>>>> >>>>>> - if (folio_batch_count(fbatch)) >>>>>> + if (nr_folios_add) { >>>>>> folio_batch_move_lru(fbatch, lru_add); >>>>>> + trace_mm_lru_add_drain(cpu, nr_folios_add); >>>>>> + } >>>>>> >>>>>> fbatch = &fbatches->lru_move_tail; >>>>>> /* Disabling interrupts below acts as a compiler barrier. */ >>>>>> @@ -928,6 +931,7 @@ static inline void __lru_add_drain_all(bool force_all_cpus) >>>>>> if (cpu_needs_drain(cpu)) { >>>>>> INIT_WORK(work, lru_add_drain_per_cpu); >>>>>> queue_work_on(cpu, mm_percpu_wq, work); >>>>>> + trace_mm_lru_drain_all_queue(cpu, force_all_cpus); >>>>> >>>>> Do you need tracing on each CPU individually, or is tracing the >>>>> entire __lru_add_drain_all() invocation sufficient? >>>> >>>> I think the latter would be fine. The remote work will invoke the >>>> mm_lru_add_drain tracepoint, which will show up as kworker stacks. Since >>>> the event already has the CPU, we could see where queued drains actually >>>> ran. >>> >>> Actually if it's just a single invocation and the only event data is the >>> force flag, a tracepoint may not even be needed. Other probes can be >>> installed on function invocation and read the single argument. I can >>> drop this from v2 and keep the single mm_lru_add_drain tracepoint. >> >> No we do want to trace the callers requesting to drain from all the CPUs. If you >> trace just lru_add_drain_cpu() then you will only see that the drain is >> requested for a given CPU but no information on the requester. >> >> Also as Barry said, I think single trace for whole __lru_add_drain_all() is good >> enough. > > Right, but couldn't that already be done with fentry or kprobe? If we > only need the calling stack and the argument value of force_all_cpus I > don't see a strong need for a dedicated tracepoint. Nevermind that. I see it's declared inline so I'll add a tracepoint and send v3.