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Tue, 03 Nov 2026 08:38:51 +0000 X-Mizu-Trace-ID: c2bade759b0e2b73 X-Migadu-Flow: FLOW_OUT Message-ID: <9cabcddf-d807-4a36-84f1-5bb06ea72aac@linux.dev> Date: Tue, 3 Nov 2026 16:38:39 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 7/7] mm/mglru: add tracepoint for inc_max_seq() To: Barry Song Cc: Steven Rostedt , Masami Hiramatsu , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Dave Chinner , Mathieu Desnoyers , Muchun Song , Qi Zheng , David Hildenbrand , Lorenzo Stoakes , Kairui Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, "open list:BPF [MISC]:Keyword:(?:b|_)bpf(?:b|_)" , Ridong Chen References: <20261103025610.3738894-1-ridong.chen@linux.dev> <20261103025610.3738894-8-ridong.chen@linux.dev> From: Ridong Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D1C8220004 X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Stat-Signature: crjbdxdwu3hb7hkm5xtm7zz1e98pgp13 X-HE-Tag: 1793695133-331113 X-HE-Meta: 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 Pyf2PIN5 QUGCJtrQo1YZroyj3NeGjqEeX4G2+TLr0BvQcUmB6dtE+cv1hvRLqvld3PnXaA9i0iaUdRtPfsEdPSi1U4wx5IeZRXGPHhVJL9e2Gwk+t3TYVxzOIXE8NbIOr6l61GD/9DuAOhIkUF2H12XlFxcYwoyS+UMXAAj+91O9YDYkQWlaz1Bv4ddAqds1nEdDcxwYSuABxf9x4ZXvLpzoqa67kd4kBRPQCn2w7dAYO675klZmzFM4DQQF/yUoFoyLi+4T+Y18jzPrSIbKEI5PmDoduh8gPGfV/a8OsTH2b1niKV+zW5JUJV15E+It1MrwhimQSUyZ67gnQNdkZ0bVpk9zP7F2Hirl95zKyj66MvuuoxO6Qdm1LrB3XS0V+5g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/3/2026 2:48 PM, Barry Song wrote: > On Tue, Nov 3, 2026 at 10:58 AM Ridong Chen wrote: >> >> From: Ridong Chen >> >> Aging in MGLRU advances max_seq via inc_max_seq(), creating a new >> youngest generation. There is currently no tracepoint on this path, so >> the moment a new generation is created, and how the min_seq of each type >> trails behind it, cannot be observed as it happens. > > We might be more interested in why aging is triggered rather > than the exact moment when max_seq is advanced. > > With your patch, we get: > > ~ # cat /sys/kernel/tracing/trace | grep mglru_inc_max_seq > a.out-93 [001] d..1. 278.276539: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=4 anon_min_seq=2 > file_min_seq=1 nr_anon={0x0,0xf016,0x12,0x0} > nr_file={0x1886,0xb,0x4c,0x0} > kswapd0-50 [000] d..1. 278.422400: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=5 anon_min_seq=2 > file_min_seq=2 nr_anon={0x5,0xccb6,0x3439,0x0} > nr_file={0x4ae,0x4f,0x55,0x0} > kswapd0-50 [000] d..1. 278.508003: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=6 anon_min_seq=3 > file_min_seq=4 nr_anon={0xccb6,0x3d29,0x1,0x0} > nr_file={0x0,0x59,0x7,0x0} > kswapd0-50 [000] d..1. 280.046056: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=7 anon_min_seq=4 > file_min_seq=5 nr_anon={0x3bf3,0xcbbd,0x23e,0x0} > nr_file={0x0,0xb,0x1,0x0} > kswapd0-50 [000] d..1. 280.124876: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=8 anon_min_seq=5 > file_min_seq=6 nr_anon={0xcafd,0x3e31,0x0,0x0} > nr_file={0x0,0x5,0x7,0x0} > a.out-96 [001] d..1. 290.629014: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=9 anon_min_seq=7 > file_min_seq=6 nr_anon={0x0,0x10615,0xb,0x0} > nr_file={0x331,0xb,0x9a,0x0} > kswapd0-50 [000] d..1. 290.653098: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=10 anon_min_seq=7 > file_min_seq=7 nr_anon={0x15,0xef23,0x18c4,0x0} > nr_file={0xb,0xb8,0x55,0x0} > a.out-96 [001] d..1. 290.684875: > mm_mglru_inc_max_seq: nid=0 memcg_id=1 max_seq=11 anon_min_seq=8 > file_min_seq=9 nr_anon={0xeee3,0x1afb,0x2,0x0} > nr_file={0x0,0x76,0x4,0x0} > > You can see that the youngest generation is always zero, > because you're just getting the newly added youngest > generation :-) > Hi Barry, Thank you very much for testing and reviewing. > This somehow suggests that the information is redundant, as > there is always a zero there. > > I suspect we'll need an additional tracepoint to show why > aging is triggered and at what sc->priority it happens. > > But do you know why you trace the moment just after aging > is completed, rather than the reason why aging is needed? > My original goal was to pair it with mm_mglru_scan_folios, to see how the aging window of each memcg moves. The per-generation anon/file nr_pages were added following your suggestion on v1. I put it at the end of inc_max_seq() because of the restart there, as max_seq and min_seq are only final after that. You make a very good point that the reason for aging is also important. So I'd like to discuss which way is better: 1) Keep mm_mglru_inc_max_seq, and add another tracepoint at the aging decision in try_to_shrink_lruvec(), reporting why aging is needed and at what sc->priority. 2) Replace mm_mglru_inc_max_seq with a single tracepoint in try_to_shrink_lruvec(), right before try_to_inc_max_seq(), reporting the reason, sc->priority, swappiness, max_seq/min_seq and the per-generation nr_pages before aging. The youngest generation is not empty at that point, and the new window after aging can still be seen from the following mm_mglru_scan_folios. Which one do you prefer? -- Best regards Ridong