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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1wIpIN-00000008wbR-3iIK; Fri, 01 May 2026 14:56:48 +0000 Date: Fri, 1 May 2026 15:56:47 +0100 From: Matthew Wilcox To: Barry Song Cc: akpm@linux-foundation.org, linux-mm@kvack.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jack@suse.cz, pfalcato@suse.de, wanglian@kylinos.cn, chentao@kylinos.cn, lianux.mm@gmail.com, kunwu.chan@gmail.com, liyangouwen1@oppo.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org Subject: Re: [PATCH v2 0/5] mm: reduce mmap_lock contention and improve page fault performance Message-ID: References: <20260430040427.4672-1-baohua@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: AEEAD140010 X-Stat-Signature: eocduy4dht363fha4bzrdsw6wgb57xt9 X-Rspam-User: X-HE-Tag: 1777647422-720235 X-HE-Meta: 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 v0Jocvae /V6+5itQ/w1mCI/XU4Q7a2DTM8mM++VqYVvCn1YsSvPSEtadK+yFin1laWtaLFf7rYm9CbiiIyf5CD2GmhRNuciAt395gBPkPuBQ90/g1gp8i4cn4m0MrzapD2ElBrP0uWqIzdILgcEmrEToZ5/WH/U1QTytDE7dEt1KJUUOwtK9bxyjHSgofciYNBDoPDAn1vJ/O+VC0ZrkOwhEg7bYWYWOEeN3sSjFSE0sMefbkMmsTfuF5iaybmSx5jrXTHaCFELtX2kLiZ4yPTUiM7Q6iyeYHpbzAfLMVIRJQYO4w+edcUq0kb+eDuj7+AlicMo+VL+41yoZh1O2YcXqIrqnwvMwvcIpAsogHlVNEqJcRKRicnAWqJdesyZODIA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 01, 2026 at 06:49:58AM +0800, Barry Song wrote: > 1. There is no deterministic latency for I/O completion. It depends on > both the hardware and the software stack (bio/request queues and the > block scheduler). Sometimes the latency is short; at other times it can > be quite long. In such cases, a high-priority thread performing operations > such as mprotect, unmap, prctl_set_vma, or madvise may be forced to wait > for an unpredictable amount of time. But does that actually happen? I find it hard to believe that thread A unmaps a VMA while thread B is in the middle of taking a page fault in that same VMA. mprotect() and madvise() are more likely to happen, but it still seems really unlikely to me.