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Tue, 16 Sep 2025 08:28:38 -0700 (PDT) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-56e5c692daesm4540326e87.26.2025.09.16.08.28.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Sep 2025 08:28:37 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 16 Sep 2025 17:28:36 +0200 To: Michal Hocko Cc: "Uladzislau Rezki (Sony)" , linux-mm@kvack.org, Andrew Morton , Baoquan He , LKML Subject: Re: [PATCH v2 04/10] mm/vmalloc: Avoid cond_resched() when blocking is not permitted Message-ID: References: <20250915134041.151462-1-urezki@gmail.com> <20250915134041.151462-5-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 796B0180016 X-Stat-Signature: pydmbomnas7c6j5dduxpa4m3y6xb3z7j X-HE-Tag: 1758036520-896345 X-HE-Meta: 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 3q6488ql 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 15, 2025 at 07:11:27PM +0200, Michal Hocko wrote: > On Mon 15-09-25 15:40:34, Uladzislau Rezki wrote: > > vm_area_alloc_pages() contains the only voluntary reschedule points > > along vmalloc() allocation path. They are needed to ensure forward > > progress on PREEMPT_NONE kernels under contention for vmap metadata > > (e.g. alloc_vmap_area()). > > > > However, yielding should only be done if the given GFP flags allow > > blocking. This patch avoids calling cond_resched() when allocation > > context is non-blocking(GFP_ATOMIC, GFP_NOWAIT). > > We do have cond_resched in the page allocator path, right? > So unless I am missing something we can safely drope these. I thought we > have discused this already. > Yes, we discussed this. I did some test with dropped cond_resched() for !PREEMPT kernel and i can trigger soft-lockups under really heavy stress load. I prefer to keep them so far for consistency. I need some time to investigate it more. As i noted in commit message, the vmalloc() path only has those two resched points. Probably i need to move them into another place later. As for page-allocator, it is in a slow path which i do not hit in my stress-setup. -- Uladzislau Rezki