linux-kernel - Re: [PATCH v1 2/2] vmalloc: Optimize vfree

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Message-ID: <aVyRR2-fdvJ_9JNy@casper.infradead.org>
Date: Tue, 6 Jan 2026 04:36:23 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>,
	Uladzislau Rezki <urezki@...il.com>,
	"Vishal Moola (Oracle)" <vishal.moola@...il.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] vmalloc: Optimize vfree

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 ...

+	for (i = 0; i < vm->nr_pages; i++) {
+		struct page *page = vm->pages[i];
+
+		if (!put_page_testzero(page)) {
+			__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.