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Fri, 24 Apr 2026 00:46:26 +0000 (UTC) Received: from mstore137.sjtu.edu.cn (unknown [10.118.0.137]) by mta91.sjtu.edu.cn (Postfix) with ESMTP id A55EF37F802; Fri, 24 Apr 2026 08:46:25 +0800 (CST) Date: Fri, 24 Apr 2026 08:46:24 +0800 (CST) From: SUVONOV BUNYOD To: Shakeel Butt Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, rostedt@goodmis.org, mhiramat@kernel.org, david@kernel.org, mhocko@kernel.org, zhengqi arch , ljs@kernel.org, mathieu desnoyers , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <1868971658.1970916.1776991584726.JavaMail.zimbra@sjtu.edu.cn> In-Reply-To: References: <20260423103753.546582-1-b.suvonov@sjtu.edu.cn> Subject: Re: [PATCH] mm/vmscan: add balance_pgdat begin/end tracepoints MIME-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 7bit X-Originating-IP: [116.230.222.59] X-Mailer: Zimbra 10.0.18_GA_4835 (ZimbraWebClient - FF149 (Linux)/10.0.18_GA_4828) Thread-Topic: mm/vmscan: add balance_pgdat begin/end tracepoints Thread-Index: FmqamJoTP0RVjIuNzdboLtlnAuPAew== X-Rspamd-Queue-Id: 206774000A X-Rspamd-Server: rspam12 X-Stat-Signature: yiguru1jgc6xktfzcf8jxmomkg7t9jm6 X-Rspam-User: X-HE-Tag: 1776991590-982034 X-HE-Meta: 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 wMMY9aGI 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Thank you for reviewing Shakeel, > Do we need to trace highest_zoneidx at the end? Can it change within > balance_pgdat()? highest_zoneidx does not change within a balance_pgdat() invocation. It is passed in as an argument and remains the classzone bound used for the balancing checks throughout the function. I kept highest_zoneidx in the end tracepoint to make the outcome event self-contained. In principle, begin/end correlation is possible, but under sustained memory pressure kswapd reclaim can be frequent enough that consumers may prefer to analyze end events directly, and any dependence on matching begin/end becomes less convenient and less robust in the presence of filtering or dropped trace records. Since nr_reclaimed and the final order are only known at the end, having highest_zoneidx there allows end-only analysis without correlating with the begin event. For example, it lets users answer questions like: - this pass reclaimed too much or too little memory; what highest_zoneidx did that result correspond to? - how much reclaim was done when balancing up to ZONE_NORMAL vs other classzone bounds? - when highest_zoneidx == ZONE_NORMAL, how often did reclaim finish at order=0? So it is there because it provides context for the end-of-reclaim result. Do you think this is sufficient justification? If not, then I can drop it from the end tracepoint in v2. ----- Original Message ----- From: "Shakeel Butt" To: "Bunyod Suvonov" Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, rostedt@goodmis.org, mhiramat@kernel.org, david@kernel.org, mhocko@kernel.org, "zhengqi arch" , ljs@kernel.org, "mathieu desnoyers" , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Sent: Friday, April 24, 2026 1:46:55 AM Subject: Re: [PATCH] mm/vmscan: add balance_pgdat begin/end tracepoints On Thu, Apr 23, 2026 at 06:37:53PM +0800, Bunyod Suvonov wrote: > Vmscan has six main reclaim entry points: try_to_free_pages() for > direct reclaim, try_to_free_mem_cgroup_pages() for memcg reclaim, > mem_cgroup_shrink_node() for memcg soft limit reclaim, node_reclaim() > for node reclaim, shrink_all_memory() for hibernation reclaim, and > balance_pgdat() for kswapd reclaim. > > All of them, except for shrink_all_memory() and balance_pgdat(), already > have begin/end tracepoints. This makes it harder to trace which reclaim > path is responsible for memory reclaim activity, because kswapd reclaim > cannot be identified as cleanly as other reclaim entry points, even > though it is the main background reclaim path under memory pressure. > There may be no need to trace shrink_all_memory() as it is primarily > used during hibernation. So this patch adds the missing tracepoint pair > for balance_pgdat(). > > The begin tracepoint records the node id, requested reclaim order, and > highest_zoneidx. The end tracepoint records the node id, reclaim order > that balance_pgdat() finished with, highest_zoneidx, and nr_reclaimed. Do we need to trace highest_zoneidx at the end? Can it change within balance_pgdat()? > Together, they show the requested reclaim order and zone bound, whether > reclaim fell back to a lower order, and how much reclaim work was done. > > Signed-off-by: Bunyod Suvonov Overall looks good.