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[90.233.206.146]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5334ea2959fsm1502393e87.43.2024.08.26.05.38.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Aug 2024 05:38:43 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 26 Aug 2024 14:38:40 +0200 To: Michal Hocko Cc: Uladzislau Rezki , Hailong Liu , Andrew Morton , Barry Song <21cnbao@gmail.com>, Christoph Hellwig , Vlastimil Babka , Tangquan Zheng , stable@vger.kernel.org, Baoquan He , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RESEND PATCH v1] mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0 Message-ID: References: <20240815220709.47f66f200fd0a072777cc348@linux-foundation.org> <20240816091232.fsliktqgza5o5x6t@oppo.com> <20240816114626.jmhqh5ducbk7qeur@oppo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 16935100014 X-Stat-Signature: f9pxpqp73gicohrqkupgormsi57zu6ky X-Rspam-User: X-HE-Tag: 1724675925-492272 X-HE-Meta: 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 FGifr5N1 KufyJPv+I0++WSI3yGdP710YmQsjmFx+m1DxnKQQ7xEP6ieksi/mBz45bbkptaXr3bSNGecGuBFS+F4e2PhloJbmD98Ri7Yv/1pT2HgjsawrNHMyfOV+PXZWVfx+Y1c2CvC7xle66vVR2Gd0wVeftW91bxMc0ncyzAe6MarDHOc2T4UghUwpoL3EvfwdFxcQJ2/jykVkelCAz1j5a6r8K7cDeejRaLTLkgh/TkbdBCC5QMSZTVrg52ovkaJ/dvD9kasHiUTRCZPMPEb+7vZ6zyok0psPMWhaI77SllOdDu+/en6DnB9nnbqSIaO5E0+U6vkyJzFj2OI1ritnnJ5+RENx+QddEp81SLXqT9PtrAsv7WzjCGkZ0x6cOa+YmCRwp30hvVgSxheV4DuopHUCMcVxdsfE4RJvG+CoE 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, Aug 26, 2024 at 09:52:42AM +0200, Michal Hocko wrote: > On Fri 23-08-24 18:42:47, Uladzislau Rezki wrote: > [...] > > @@ -3666,7 +3655,16 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, > > set_vm_area_page_order(area, page_shift - PAGE_SHIFT); > > page_order = vm_area_page_order(area); > > > > - area->nr_pages = vm_area_alloc_pages(gfp_mask | __GFP_NOWARN, > > + /* > > + * Higher order nofail allocations are really expensive and > > + * potentially dangerous (pre-mature OOM, disruptive reclaim > > + * and compaction etc. > > + * > > + * Please note, the __vmalloc_node_range_noprof() falls-back > > + * to order-0 pages if high-order attempt has been unsuccessful. > > + */ > > + area->nr_pages = vm_area_alloc_pages(page_order ? > > + gfp_mask &= ~__GFP_NOFAIL : gfp_mask | __GFP_NOWARN, > > node, page_order, nr_small_pages, area->pages); > > > > atomic_long_add(area->nr_pages, &nr_vmalloc_pages); > > > > > > Is that aligned with your wish? > > I am not a great fan of modifying gfp_mask inside the ternary operator > like that. It makes the code harder to read. Is there any actual reason > to simply drop GFP_NOFAIL unconditionally and rely do the NOFAIL > handling for all orders at the same place? > 1. So, for bulk we have below: /* gfp_t bulk_gfp = gfp & ~__GFP_NOFAIL; */ I am not sure if we need it but it says it does not support it which is not clear for me why we have to drop __GFP_NOFAIL for bulk(). There is a fallback to a single page allocator. If passing __GFP_NOFAIL does not trigger any warning or panic a system, then i do not follow why we drop that flag. Is that odd? 2. High-order allocations. Do you think we should not care much about it when __GFP_NOFAIL is set? Same here, there is a fallback for order-0 if "high" fails, it is more likely NO_FAIL succeed for order-0. Thus keeping NOFAIL for high-order sounds like not a good approach to me. 3. "... at the same place?" Do you mean in the __vmalloc_node_range_noprof()? __vmalloc_node_range_noprof() -> __vmalloc_area_node(gfp_mask) -> vm_area_alloc_pages() if, so it is not straight forward, i.e. there is one more allocation: static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, pgprot_t prot, unsigned int page_shift, int node) { ... /* Please note that the recursion is strictly bounded. */ if (array_size > PAGE_SIZE) { area->pages = __vmalloc_node_noprof(array_size, 1, nested_gfp, node, area->caller); } else { area->pages = kmalloc_node_noprof(array_size, nested_gfp, node); } ... } whereas it is easier to do it inside of the __vmalloc_area_node(). > > Not that I care about this much TBH. It is an improvement to drop all > the NOFAIL specifics from vm_area_alloc_pages. > I agree. I also do not like modifying gfp flags on different levels and different cases. To me there is only one case. It is high-order requests with NOFAIL. For this i think we should keep our approach, i mean dropping NOFAIL and repeat because we have a fallback. -- Uladzislau Rezki