From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 7705B37FF76; Wed, 17 Jun 2026 11:11:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781694683; cv=none; b=F3tZo4bk8bcxzOi1oFm+wZISmYvMyQkX7huud7Zy6+mceUTsNoiqGjfubziaYh77/DF9FZPKhKqa+lNm6typOFHr85K4zT5Azxt1oXQ5Il4o/4nFKUg6holTTvo9WicQOJkN9Na5gJHxYxING/oKzBn5aS+xv0Rp77I+pBqg13A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781694683; c=relaxed/simple; bh=baqqMi0HbpVGro7oJjM4kRgehZNRoXZThuBkUG5xkfM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WjqYQK8/HvMeHLod65jb909oKHJK+VRWxkM9ekTeGmI5xkohEOSLBJan+IdVlF2TRdE6V9isuUBqJzbMF6CpxuYYd0sy/pUqT7q/7DVDmHzOt7DsfSE8DqHLmJwN/6YaBL/YaH6W4fRZ/sZz4uhQow1OEMMyjYUpqeqDSi0/Kc8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L2GISETD; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="L2GISETD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 511181F000E9; Wed, 17 Jun 2026 11:11:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781694682; bh=SiaKWxtsrJCVgybVhz4X8gHJGp58KurwzLbmq6ogImQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=L2GISETDR7ytjswxWuQiaw6cu9KE+dOUjms263mMicLABEo1Ubjx5XRDqidUmu+P5 E+DNoNpojjUwY50aQisyeFc8e4pQWCcB2XFFkj/b5ZgDIDHwM4teqOIeoVDQ6RFk+8 +EuMiRth+LUSq2hVlr+ZBw/4XB1HKemkbdrfV9UBzs2pTiUilN9yMPYhh3MGBs+WZh nWrTcJbkdY9IIyVtJwXLVhXUM1onmEXFtpauv5b2QRU8yr1ei2HU/rfVNKZYdUEaBz ffdC4rcEP1px/qGJnjFm+SJV3akJOsaCrpsHpj+ZdlWUQus1N0gqfq9PxQoNg+nstt WMf6nHHMZhrfg== Message-ID: <06122cae-e28b-4ded-a9dd-d380d31c5230@kernel.org> Date: Wed, 17 Jun 2026 13:11:16 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/lruvec: trace LRU add drains and drain-all requests To: JP Kobryn , linux-mm@kvack.org, willy@infradead.org, shakeel.butt@linux.dev, 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, baohua@kernel.org, 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 Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org References: <20260610195220.12403-1-jp.kobryn@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/10/26 21:52, 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_add_drain_all to capture callers of __lru_add_drain_all and > whether they set the force flag for all CPUs. The tracepoint resembles > the signature of the enclosing function, but is needed because of > potential inlining. > > Signed-off-by: JP Kobryn > --- > include/trace/events/pagemap.h | 37 ++++++++++++++++++++++++++++++++++ > mm/swap.c | 7 ++++++- > 2 files changed, 43 insertions(+), 1 deletion(-) > > diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h > index 171524d3526d..ff3da07ccb40 100644 > --- a/include/trace/events/pagemap.h > +++ b/include/trace/events/pagemap.h > @@ -77,6 +77,43 @@ 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_add_drain_all, > + > + TP_PROTO(bool force_all_cpus), > + > + TP_ARGS(force_all_cpus), > + > + TP_STRUCT__entry( > + __field(bool, force_all_cpus ) > + ), > + > + TP_fast_assign( > + __entry->force_all_cpus = force_all_cpus; > + ), > + > + TP_printk("force_all_cpus=%s", > + __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..e14b7612f896 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. */ > @@ -869,6 +872,8 @@ static inline void __lru_add_drain_all(bool force_all_cpus) > if (WARN_ON(!mm_percpu_wq)) > return; > > + trace_mm_lru_add_drain_all(force_all_cpus); > + > /* > * Guarantee folio_batch counter stores visible by this CPU > * are visible to other CPUs before loading the current drain Given that trace events can quickly become stable ABI [1], are we really sure we want to add this? [1] https://lore.kernel.org/r/20260603130006.7d2c4a62@gandalf.local.home -- Cheers, David