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[109.81.87.166]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49996100184sm300612795e9.1.2026.08.18.07.08.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2026 07:08:20 -0700 (PDT) Date: Tue, 18 Aug 2026 16:08:19 +0200 From: Michal Hocko To: Leon Hwang Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , linux-kernel@vger.kernel.org, Lance Yang Subject: Re: [PATCH] mm: add cond_resched() to free_pud_range() Message-ID: References: <20260818134934.92354-1-leon.hwang@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260818134934.92354-1-leon.hwang@linux.dev> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5C46F20008 X-Stat-Signature: d1ykx3ns3iqdswi7rorsok5hz9jdrftp X-HE-Tag: 1787062102-970669 X-HE-Meta: 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 AkADo5ii JLpuOzhW53Frp2BwmyUtKg+ccTdfBq8A18ZXBu/5+Ec4KQpMWfu8xoCna11N7xaOfmwhg6z2XEOZeUAHPheKg75Vu19WlJY9UkQP1HVQc/hs1cuOKzCqTRsCR9lBU7WccgBu3Hs0R64fIbdS5a1Bxahufd3lynNSksC4UFK6QyImfsc0KF3On0Y71mI8Cr3yPEIVZpo0KW5hwhtAWVVirJ8RlmzCxS712VnnxXbt+nAbmHeydhaRicd7HfXF/Lmx3sZHg+FWQaXPwBefACc8iNjsVrZSM5dzgYZPV2B5jRIDSG8ZoWQcvY41oOAEmc+wgys2bE46vfxsAvTA7H+qwmnVCbq6EssHLuF7DB3LiR924tcFJN2UrXeoc4XCMjtJESvkfilmwOtz/77i7n0MAbNARtQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue 18-08-26 21:49:34, Leon Hwang wrote: > Packet receive timeouts were seen in production. Tracing showed that an > exiting process with a sparse 2.5 TiB mapping could remain in kernel > context for over 20 ms without reaching a scheduling point while > freeing PTE page-table pages. Hard IRQs could still be handled, but the > per-CPU ksoftirqd thread and other runnable tasks could not run during > that interval, delaying NET_RX softirq work queued to ksoftirqd. > > Like zap_pud_range(), add cond_resched() to free_pud_range() so > ksoftirqd and other runnable tasks can run between PUD entries. Testing > with PREEMPT_NONE showed that the maximum interval between scheduling > points fell from over 20 ms to below 2 ms. PREEMPT_NONE is effectivelly dead and most cond_resched will/should be removed. Is there any reason why you are not using full preemption when requiring low latencies? > Reported-by: Lance Yang > Tested-by: Lance Yang > Signed-off-by: Leon Hwang > --- > mm/memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 4134ac607ee0..68c15449de07 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -231,7 +231,7 @@ static inline void free_pud_range(struct mmu_gather *tlb, p4d_t *p4d, > if (pud_none_or_clear_bad(pud)) > continue; > free_pmd_range(tlb, pud, addr, next, floor, ceiling); > - } while (pud++, addr = next, addr != end); > + } while (pud++, cond_resched(), addr = next, addr != end); > > start &= P4D_MASK; > if (start < floor) > -- > 2.55.0 -- Michal Hocko SUSE Labs