From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794257786; b=w8eDwscr0YcboocPCtA01BpN44yFqbRsdpCSJHaNIX/UUexSDak4uNzJ4WJv3rSlE3M5 G5OpDkIEmULkFp9VzuHkJxGvnNXdSt+JeHyCs+xDlQApecaVXgZczmXAX1gP0XVm1xgkI b/xfXuc9i6bD5SYpByMleANh91S0LPiFZddN+temRn7VJOK1klSCCf9+MJVi9hY2cKpSU zNnCLJqWn3XZg4t+qiKD+IM/JZWSPqRBxg5qBEyN5KIQYrk7B3Us+ibqPneQb2zP8JHXn n17lCR4u8n3IdNuMFi9y5XPBQajl46fRkXi6eUSKcn+/x/0iNYvbwJxS2h5d6d6kAjA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794257786; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=ZfwEzavV+xYJ/qlHoaoW30drhhxmWDviLHuBnnT384U=; b=g9nDhLguPoVrjTVCu/Nvt4bB2LWBZ6uKzwtUfoyGCI4VKev0p0grxA2cipg9xsSy74qx sBj1G4V6t4/6Kmf46FwlaYmHEnoQ/ohp3XvftYD6WKNyaS8SjryzYF79tprYv+vO+jKxZ Q5U4ZdTcrU2TN7pGEuWp6wibVO89+uOUlAv7WsCOFkiuYB/UnBwD+fH8CLItxESelMb7z P4WbUczuxDHyGerReAMIPRyJRhYUa6rH2udYjubv9HiHD7PSotYK64ZEZQ76/VnktuidZ 6HbHT+Vs+QUM/vGVlx16SX193nkQJrx+QfonAQo14whMXbAsNObmyK7DmOyjnnvC8mA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=YEkoK3pY; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8A749606A321 for ; Mon, 9 Nov 2026 20:56:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=YEkoK3pY Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6FA531F0089F; Mon, 9 Nov 2026 20:56:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794257786; bh=ZfwEzavV+xYJ/qlHoaoW30drhhxmWDviLHuBnnT384U=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=YEkoK3pYgClUuurovjn4IRR4mD2Txlxhmoqa/G7rZ2+e5q79pDBdqXxcOJ7krJoLC jU/pFUNYJBiw7JU7g2pDOSCZTuCE7qe+vtOQMrqMkhZ8UO1JaBM//NADZjubtzhhmv zuX6rFq4/4dua65IihVrqaX+thOtlpxYZ1+vU5U16Nw6379xCIiI7EtKdCxTWwj0lQ wBdd8qSxJu5v+k66EBIO4MvWDERzHQyBkSClYKFvY6K1ZrJoeW32j9b1/kJrUZTwPL X/N5Z3sj/QnUEQLZPqIyMu63iQGqFk6bauZjiaSYlpVwUhpncuvIorL9DzZQo0nrCU 019r3x59lRrrw== Message-ID: <4acf6df8-8cdf-4f71-830d-9233db151b2a@kernel.org> Date: Mon, 9 Nov 2026 21:56:20 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/cma: simplify cma_declare_contiguous_multi() To: "Mike Rapoport (Microsoft)" , Andrew Morton Cc: Ivy Lopez , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261106-cma-multi-v1-1-054eae6e2c1c@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20261106-cma-multi-v1-1-054eae6e2c1c@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/6/26 13:56, Mike Rapoport (Microsoft) wrote: > When cma_declare_contiguous_multi() cannot allocate a CMA area as a > single range, it falls back to collecting a list of up to CMA_MAX_RANGES > largest free ranges above 4G, reserves them in memblock and adds them to > cma->ranges. > > The list and subsequently cma->ranges are supposed to be sorted in the > order of base addresses of the "allocated" ranges. > > This implementation has two bugs: > > * The allocation may fail even when there is enough free memory because > list_insert_sorted() sorts the list in the wrong order. > > When the list is full, the largest range is evicted rather than the > smallest, the final list is not sorted by address, and the smallest > ranges are used first. > > * the function may report success while it reserved less memory than > requested because sizesum accounts for ranges that were skipped. > > And overall it is a lot of list management and open coded range > selection for no real gain. > > Replace the current code with a loop that finds the largest free range > above 4G, reserves as much of it as needed and repeats until the entire > area is reserved or CMA_MAX_RANGES ranges are used. > > After successful alocation sort the cma->ranges by their base address. > > The new code scans free memory once for every range rather than once > for all ranges, so it is slightly slower, but it is way simpler and more > robust. > > Fixes: c009da4258f9 ("mm, cma: support multiple contiguous ranges, if requested") > Reported-by: Ivy Lopez > Closes: https://lore.kernel.org/all/cover.1792032699.git.skunkolee@gmail.com > Signed-off-by: Mike Rapoport (Microsoft) > --- [...] Quite the simplification :) > int __init cma_declare_contiguous_multi(phys_addr_t total_size, > phys_addr_t align, unsigned int order_per_bit, > const char *name, struct cma **res_cma, int nid) > { > - phys_addr_t start = 0, end; > - phys_addr_t size, sizesum, sizeleft; > - struct cma_init_memrange *mrp, *mlp, *failed; > + unsigned long size_mb = (unsigned long)total_size / SZ_1M; Nit: could be const. > + phys_addr_t size, remaining, size_align; > struct cma_memrange *cmrp; > - LIST_HEAD(ranges); > - LIST_HEAD(final_ranges); > - struct list_head *mp, *next; > - int ret, nr = 1; > - u64 i; > + phys_addr_t start = 0; > struct cma *cma; > + int nr = 0; > + int ret; > > /* > * First, try it the normal way, producing just one range. > */ > ret = __cma_declare_contiguous_nid(&start, total_size, 0, align, > order_per_bit, false, name, res_cma, nid); > + if (!ret) { > + pr_info("Reserved %lu MiB at %pa\n", size_mb, &start); > + return 0; > + } > if (ret != -ENOMEM) > - goto out; > + goto err; > > /* > * Couldn't find one range that fits our needs, so try multiple > @@ -572,151 +556,56 @@ int __init cma_declare_contiguous_multi(phys_addr_t total_size, > * aligned to @align, and a size that is aligned to > * both @align and @order_to_bit, things will work out. > */ > - nr = 0; > - sizesum = 0; > - failed = NULL; > - > ret = cma_new_area(name, total_size, order_per_bit, &cma); > - if (ret != 0) > - goto out; > + if (ret) > + goto err; > > align = max_t(phys_addr_t, align, CMA_MIN_ALIGNMENT_BYTES); > - /* > - * Create a list of ranges above 4G, largest range first. > - */ > - for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &start, &end, NULL) { > - if (upper_32_bits(start) == 0) > - continue; > - > - start = ALIGN(start, align); > - if (start >= end) > - continue; > - > - end = ALIGN_DOWN(end, align); > - if (end <= start) > - continue; > + size_align = max_t(phys_addr_t, align, PAGE_SIZE << order_per_bit); > > - size = end - start; > - size = ALIGN_DOWN(size, (PAGE_SIZE << order_per_bit)); > + remaining = total_size; > + while (remaining && nr < CMA_MAX_RANGES) { > + size = cma_find_free_range(align, size_align, nid, &start); That's more a memblock helper than a cma helper :) [...] > + /* allocate from lower addresses first */ > + sort(cma->ranges, nr, sizeof(cma->ranges[0]), cma_range_cmp, NULL); That's nice. Acked-by: David Hildenbrand (Arm) -- Cheers, David