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Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , 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-Stat-Signature: cnk54nm91gmck8we1q8zfximtbtodsdt X-Rspamd-Queue-Id: 11BCC20002 X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1787062181-233882 X-HE-Meta: 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 HtbF2IQh ormrmfYSlU55QmXmQ1jDWFGwmR3MEwuoGUXDJ29KuX/KBj4km3UOPLYMvHy96Ri1Ed+l9NI1j56VXyT/iwo+B86ev3yGN28DRMftn5uPs3ASDnV8yvK+YfvFwojupln+kU1MOszomOzb4cohdAywMcq0SIYqiLoKS3wlv6Er7LXA/7nqUfBvtlJzr0PZaSKk+m4hdBn1OAqxl/xql+4PrBsaiqqilH6zqz8R9numpN3CElZLgHQQtFxAyxkyHydpBBcULHfIUbh97y0z/oZWc+BGJC9sApunWTXjmPm2932I5e/o= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 18, 2026 at 09:49:34PM +0800, 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. > > 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); This is really obscure, can't it be in the loop body? > > start &= P4D_MASK; > if (start < floor) > -- > 2.55.0 > > -- Sincerely yours, Mike.