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Tue, 16 Sep 2025 22:22:02 -0700 (PDT) Received: from pc636 ([2001:9b1:d5a0:a500::800]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5779b5d6928sm233405e87.131.2025.09.16.22.22.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Sep 2025 22:22:02 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 17 Sep 2025 07:22:00 +0200 To: Michal Hocko Cc: Uladzislau Rezki , 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: E4E944000A X-Stat-Signature: rmphju7wh6j93fnzqn4kwemaehspui7j X-HE-Tag: 1758086524-518251 X-HE-Meta: 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 /omH2FyQ 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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 Tue, Sep 16, 2025 at 08:08:18PM +0200, Michal Hocko wrote: > On Tue 16-09-25 17:28:36, Uladzislau Rezki wrote: > > 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. > > OK, so the fast path can trigger the soft lockup? If yes please mention > that in the changelog so that we know why this is needed. With that > included feel free to add > Acked-by: Michal Hocko > We, in vmalloc(), also have a slow path. Those two points seem to help. I will move them later to alloc_vmal_area(), after a slow path serves a request. Thank you! -- Uladzislau Rezki