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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432bd5ff1e9sm3541857f8f.41.2026.01.06.01.47.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Jan 2026 01:47:32 -0800 (PST) Date: Tue, 6 Jan 2026 09:47:27 +0000 From: David Laight To: Matthew Wilcox Cc: Ryan Roberts , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Uladzislau Rezki , "Vishal Moola (Oracle)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 2/2] vmalloc: Optimize vfree Message-ID: <20260106094727.5bea5ed6@pumpkin> In-Reply-To: References: <20260105161741.3952456-1-ryan.roberts@arm.com> <20260105161741.3952456-3-ryan.roberts@arm.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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-Transfer-Encoding: 7bit On Tue, 6 Jan 2026 04:36:23 +0000 Matthew Wilcox wrote: > On Mon, Jan 05, 2026 at 04:17:38PM +0000, Ryan Roberts wrote: > > + if (vm->nr_pages) { > > + start_pfn = page_to_pfn(vm->pages[0]); > > + nr = 1; > > + for (i = 1; i < vm->nr_pages; i++) { > > + unsigned long pfn = page_to_pfn(vm->pages[i]); > > + > > + if (start_pfn + nr != pfn) { > > + __free_contig_range(start_pfn, nr); > > + start_pfn = pfn; > > + nr = 1; > > + cond_resched(); > > + } else { > > + nr++; > > + } > > It kind of feels like __free_contig_range() and this routine do the same > thing -- iterate over each page and make sure that it's compatible with > being freed. What if we did ... > nr = 0; > + for (i = 0; i < vm->nr_pages; i++) { > + struct page *page = vm->pages[i]; > + > + if (!put_page_testzero(page)) { Do you need an if (nr) here? If nothing else something might complain about start_page being unset. Is this a common/expected path? If not I think you can just 'continue' and it all still look ok. There is also a cond_reshed() below, if a common path should there be one here? > + __free_frozen_contig_pages(start_page, nr); > + nr = 0; > + continue; > + } > + > + if (!nr) { > + start_page = page; > + nr = 1; > + continue; > + } > + > + if (start_page + nr != page) { > + __free_frozen_contig_pages(start_page, nr); > + start_page = page; > + nr = 1; > + cond_resched(); > + } else { > + nr++; > + } > + } > + > + __free_frozen_contig_pages(start_page, nr); > > That way we don't need to mess around with returning the number of pages > not freed. > I think this shorter form is equivalent. nr = 0; start_page = NULL; for (i = 0; i < vm->nr_pages; i++) { struct page *page = vm->pages[i]; if (!put_page_testzero(page)) continue; if (start_page + nr != page) { if (nr) { __free_frozen_contig_pages(start_page, nr); cond_resched(); } start_page = page; nr = 1; } else { nr++; } } if (nr) __free_frozen_contig_pages(start_page, nr); David