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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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