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Peter Anvin" , Andrew Morton , Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Uladzislau Rezki , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Clark Williams , suleiman@google.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-rt-devel@lists.linux.dev Subject: Re: [RFC 06/10] Reclaim memory from blocked kernel stacks Message-ID: <20260828150836.2d5b378c@gandalf.local.home> In-Reply-To: <20260828151018.HnR9xV1N@linutronix.de> References: <20260827232948.2520558-1-stevensd@google.com> <20260827232948.2520558-7-stevensd@google.com> <20260828133620._x2XfJR_@linutronix.de> <20260828135947.GU776954@noisy.programming.kicks-ass.net> <20260828151018.HnR9xV1N@linutronix.de> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1+hstgiEjxGj1qjeta+VJO9YmsPembJtic= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=iz9Z9bs2yaO0uX8X+NUUGGiRu5Z62aRatCnxgmGQF+g=; b=PAuX2eumiKoGnLpY5f2+nm1ZATl/EOmUjI/FpV343XmFEFbowkFJmql3TZ1jDF1zuxI7uBH2uMShSP5U+TAscRfUBR9oh1x+t0dQtAljRuUvKaoZDY8JWuPoBS97OtDAg2ak8UoAQy18o2uUlaGBaHG6dRHa85Cm1TzLH79+Sx8= X-HE-Meta: U2FsdGVkX18U+OOzmbS2v7qR7lqORVcgk0uJsd4pkhcItvYG+24rlhF4ua5cRunBcYiDvk8rYgLbmXs/0MxeE0s/dEd+FjrLEJn/AycQVURIxyo4rzRtjDYatkcwbpTyQECqMN/Wus6AbwXpziKNmrDRuLR04URK1/zW97dGFmeH7TWUpmWhcqBpwYZ8VgsB4W5dK++Zbf3JGighkdJdtKpSkazEYldOZbb5m9xR/iLZO8WEUXb4LaN8UmW7msMMHKqS7eR1vXglMkO6vofVREg91wkxVK9Hwf4/gjRglGRSo4pZTEeZNnJ/wPnaBfJI X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 53E5A20003 X-Stat-Signature: a7a484t7i19zh7qddat4jhesanu3dx79 X-HE-Tag-Orig: 1787944066-559064 X-HE-Tag: 1787944079-346803 X-HE-Meta: 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 ALUgSnwW 4ADCFKXlropF1wUiPjDU+Hk2cIamFIsNoOnsboiBztYR8RtlCCuN61ImsOg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 28 Aug 2026 17:10:18 +0200 Sebastian Andrzej Siewior wrote: > > THREAD_SIZE_ORDER 2 > > THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER) > >=20 > > that makes for 4 pages. =20 >=20 > Oh. I wasn't aware that we have 16kib stacks these days. But looking > at it we have it now for over 10 years=E2=80=A6 Judging from 6538b8ea886e4 > ("x86_64: expand kernel stack to 16K") it might be temporary and things > are better now? Arm64 has a different story according to 845ad05ec31e0 > ("arm64: Change kernel stack size to 16K"). Risc-V also mentions "for > now" in 0cac21b02ba5f ("riscv: use 16KB kernel stack on 64-bit"). >=20 > I just booted my XFS kvm box and did things and 8KiB works so far. If you want to see how big your stack is and where its used, you can run the stack tracer: # trace-cmd stack --start [wait] # trace-cmd stack (stack tracer running) Depth Size Location (41 entries) ----- ---- -------- 0) 5032 48 choose_idle_cpu+0x5/0x100 1) 4984 296 select_task_rq_fair+0xa84/0x2b40 2) 4688 104 try_to_wake_up+0x168/0x7e0 3) 4584 16 task_work_add+0xd7/0xf0 4) 4568 16 io_req_normal_work_add+0x75/0xb0 5) 4552 40 io_poll_wake+0x10f/0x160 6) 4512 64 __wake_up_common+0x72/0xa0 7) 4448 40 __wake_up_sync_key+0x43/0x60 8) 4408 24 sock_def_readable+0x46/0xe0 9) 4384 80 tun_net_xmit+0x240/0x550 [tun] 10) 4304 80 dev_hard_start_xmit+0x63/0x1e0 11) 4224 256 __dev_queue_xmit+0x880/0x10b0 12) 3968 24 br_dev_queue_push_xmit+0x62/0xf0 [bridge] 13) 3944 80 br_dev_xmit+0x15e/0x4a0 [bridge] 14) 3864 80 dev_hard_start_xmit+0x63/0x1e0 15) 3784 256 __dev_queue_xmit+0x880/0x10b0 16) 3528 72 ip_finish_output2+0x2ce/0x650 17) 3456 104 ip_output+0x63/0x110 18) 3352 72 __ip_queue_xmit+0x16f/0x470 19) 3280 232 __tcp_transmit_skb+0xcb5/0x1140 20) 3048 120 tcp_write_xmit+0x5aa/0x1760 21) 2928 24 __tcp_push_pending_frames+0x39/0x110 22) 2904 104 tcp_rcv_established+0x37f/0xeb0 23) 2800 32 tcp_v4_do_rcv+0x13f/0x300 24) 2768 168 tcp_v4_rcv+0xc01/0x1300 25) 2600 48 ip_protocol_deliver_rcu+0x35/0x1b0 26) 2552 24 ip_local_deliver_finish+0x85/0x100 27) 2528 40 __netif_receive_skb_one_core+0x85/0xa0 28) 2488 56 netif_receive_skb+0x127/0x180 29) 2432 104 br_handle_frame_finish+0x428/0x680 [bridge] 30) 2328 40 br_handle_frame+0x132/0x2a0 [bridge] 31) 2288 280 __netif_receive_skb_core.constprop.0+0x16e/0xdf0 32) 2008 40 __netif_receive_skb_one_core+0x39/0xa0 33) 1968 56 netif_receive_skb+0x127/0x180 34) 1912 256 tun_get_user+0xbd0/0x1260 [tun] 35) 1656 56 tun_chr_write_iter+0x77/0xba [tun] 36) 1600 88 do_iter_readv_writev+0x161/0x260 37) 1512 256 vfs_writev+0x168/0x3c0 38) 1256 80 do_writev+0x7f/0x110 39) 1176 984 do_syscall_64+0xaa/0x670 40) 192 192 entry_SYSCALL_64_after_hwframe+0x76/0x7e Note, it only monitors task context (not interrupt). -- Steve