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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: <20260831065509.qqEtERDB@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> <20260828150836.2d5b378c@gandalf.local.home> <20260828151313.5c4a5e4b@gandalf.local.home> <20260828151747.20035d50@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260828151747.20035d50@gandalf.local.home> X-Stat-Signature: pwxk4e45jiq3t8ue6m4ufaq7cpwhc6t4 X-Rspamd-Queue-Id: 6BB6618000A X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1788159313-998130 X-HE-Meta: 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 TNBCdpty pRTgx/K0BnHxWeCABb4j1HVICpsNGjMg/5WQKZ6bC8VCyxT3jUrhsYI320BljbwBFZBsljoebaMmQlfuvfHJLkjGyevR3MotP6BWsFSrjh4uCX0MYNNX0Vs+U93jZhz8kdRYmGipjjkP0fgU0LhdIY7JWl47LEhLPYrzg89H8Gw65r8MKEgeowY7ejQ1DuDdCVAbwuqXQh+hLgfTyHpD5zTKRqTwX/ninFjHIbbUpaXjDjStN0rNcEjE4qL8Mf0jGkWuH Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026-08-28 15:17:47 [-0400], Steven Rostedt wrote: > On Fri, 28 Aug 2026 15:13:13 -0400 > Steven Rostedt wrote: > > > If one worries about stack size, they may want to turn off > > CONFIG_RANDOMIZE_KSTACK_OFFSET as I see some big numbers for do_syscall_64() > > And the scheduler has some heavy stack usage here! > > # trace-cmd stack > (stack tracer running) > Depth Size Location (31 entries) > ----- ---- -------- > 0) 8120 48 __msecs_to_jiffies+0x9/0x30 I didn't expect get_user_pages_unlocked() getting that big: (stack tracer running) Depth Size Location (60 entries) ----- ---- -------- 0) 8176 48 __css_rstat_updated+0x9/0x150 1) 8128 8 __cgroup_account_cputime+0x2f/0x50 2) 8120 48 update_se+0x10c/0x1b0 3) 8072 48 update_curr+0x31/0x180 4) 8024 56 put_prev_entity+0x153/0x1f0 5) 7968 136 pick_next_task_fair+0x684/0x8e0 6) 7832 120 __schedule+0x1ca/0x1130 7) 7712 8 preempt_schedule_irq+0x38/0x60 8) 7704 72 irqentry_exit+0x148/0x6b0 9) 7632 136 asm_sysvec_apic_timer_interrupt+0x1a/0x20 10) 7496 240 HUF_compress1X_usingCTable_internal_bmi2+0x12d2/0x1c40 11) 7256 80 HUF_compress4X_usingCTable_internal+0x192/0x1d0 12) 7176 32 HUF_compressCTable_internal+0x61/0x90 13) 7144 136 HUF_compress_internal+0x2d2/0x500 14) 7008 56 HUF_compress4X_repeat+0x25/0x60 15) 6952 176 ZSTD_compressLiterals+0x1ad/0x400 16) 6776 224 ZSTD_entropyCompressSeqStore_internal+0xfb/0x320 17) 6552 112 ZSTD_compressBlock_internal+0x11b/0x210 18) 6440 296 ZSTD_compressContinue_internal+0x232/0xdd0 19) 6144 56 ZSTD_compressEnd_public+0x27/0x190 20) 6088 112 ZSTD_compressStream2+0x9fc/0xa60 21) 5976 80 ZSTD_compress2+0x83/0xd0 22) 5896 24 zstd_compress+0x3d/0x70 [zram] 23) 5872 72 zcomp_compress+0x62/0x90 [zram] 24) 5800 144 zram_submit_bio+0x558/0xb00 [zram] 25) 5656 128 __submit_bio+0x164/0x240 26) 5528 96 submit_bio_noacct_nocheck+0x134/0x390 27) 5432 64 bio_await+0xa7/0xb0 28) 5368 16 submit_bio_wait+0x16/0x20 29) 5352 184 swap_writepage_bdev_sync.isra.0+0x12e/0x230 30) 5168 40 swap_writeout+0x18d/0x2e0 31) 5128 176 shmem_writeout+0x286/0x530 32) 4952 440 shrink_folio_list+0x588/0xfc0 33) 4512 296 evict_folios+0x399/0xac0 34) 4216 160 try_to_shrink_lruvec+0x1a4/0x390 35) 4056 64 shrink_one+0xc0/0x1a0 36) 3992 240 shrink_node+0xa9a/0xcf0 37) 3752 88 do_try_to_free_pages+0xb3/0x4d0 38) 3664 176 try_to_free_pages+0xce/0x220 39) 3488 264 __alloc_pages_slowpath.constprop.0+0x8cc/0x1240 40) 3224 96 __alloc_frozen_pages_noprof+0x2f6/0x340 41) 3128 64 alloc_pages_mpol+0xb6/0x190 42) 3064 56 vma_alloc_folio_noprof+0x6e/0xd0 43) 3008 80 do_anonymous_page+0x32e/0x8f0 44) 2928 224 __handle_mm_fault+0xb31/0xf60 45) 2704 64 handle_mm_fault+0xee/0x2f0 46) 2640 152 __get_user_pages+0x1b5/0x1140 47) 2488 104 get_user_pages_unlocked+0xf0/0x330 48) 2384 128 hva_to_pfn+0x2ea/0x450 [kvm] 49) 2256 64 __kvm_faultin_pfn+0x61/0x90 [kvm] 50) 2192 120 kvm_mmu_faultin_pfn+0x2cf/0x6f0 [kvm] 51) 2072 24 kvm_tdp_page_fault+0x94/0xf0 [kvm] 52) 2048 120 kvm_mmu_do_page_fault+0x1d9/0x210 [kvm] 53) 1928 200 kvm_mmu_page_fault+0x7e/0x7b0 [kvm] 54) 1728 40 npf_interception+0xba/0x240 [kvm_amd] 55) 1688 168 kvm_arch_vcpu_ioctl_run+0x931/0x1900 [kvm] 56) 1520 200 kvm_vcpu_ioctl+0x2e4/0xa10 [kvm] 57) 1320 56 __x64_sys_ioctl+0x97/0xe0 58) 1264 1072 do_syscall_64+0xe1/0x640 59) 192 192 entry_SYSCALL_64_after_hwframe+0x76/0x7e Does this stack tracer distinguish between the kernel-stack and IRQ-stack? I would expect asm_sysvec_apic_timer_interrupt() on the IRQ-stack and not adding weight to the kernel stack. Given how close this is to 8192, I don't think two stack pages will happen soon. Sebastian