From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E65C61A683D; Mon, 1 Jun 2026 12:50:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780318226; cv=none; b=WtRns0fF8PExWsPO2QQx9vuoDCT2/OxbEri7t5CcYctUsqXwrtfQQb7H83WbywKsw6OJuHYwv77KPNa76HyI3VNpJXvd3k3Lb/xbVtHp792dYbLLegWOxMl/WVh2vjMQX8vTrX1QKBY7b+Kc5XvK1HxYm+W4Hnut8H9+Eib6i+0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780318226; c=relaxed/simple; bh=Xw5SifiO8sPqenzU/bTeLa9arbIsDrOONM4GL/6ZyP8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hrFPl0qbqhAOwHafFLwZz+VC2u581K9Pvt0PCDZviYfOjsXDmFEBec24UsH9d/xoTl0X5vnI+fRmWp4GsW0hVDliX6LWVFsGzR+ZnFoxbX3+fqMePFRZkkFFA9g5e1csD+3hTwSZ5UD+M5Cg/ZMvkK7kqXxQFwpK887bsjiqvqc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iRzWzLox; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iRzWzLox" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D50B81F00893; Mon, 1 Jun 2026 12:50:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780318225; bh=NiO5RIOjFIjhX80InovlNJiMWsaq00sNfFpnk2xz4IU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iRzWzLoxQbdLcwQM9CdEweJdKhVuPzgfMWkbGxgQp03XaBS6MW1UO2dMb1zXTv8gf Lc37QA55GKb4mm3qFObJW4zQf7Pz9qC7xV6ikZyYxHWeXlpofGZ8kKZRfyHkVJtovX c2ZkuL1UYH+UTxuATU7dzZzfpA6IEKpFDWOB6hVdJaxSbAlTvcO0HpBEBh4M1IOiWK xME9N7IGEufKWMYRgGc4BLlvBFLWjK3g3gy4mJixcfwwu9iob8jkrzwNnj/CAUTDZA b3Bt2jxBtQkY2ceqVr80cx5EueZj8hSqFEYX6B+N8EfmU7ZAiX0ieACScg+Y4VnUDc WH8lM0xfD2KIA== Message-ID: Date: Mon, 1 Jun 2026 14:50:19 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slab: improve kmem_cache_alloc_bulk Content-Language: en-US To: Christoph Hellwig Cc: Harry Yoo , Andrew Morton , Mark Brown , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Jesper Dangaard Brouer , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, io-uring@vger.kernel.org, kasan-dev@googlegroups.com, bpf@vger.kernel.org, netdev@vger.kernel.org, Alexander Lobakin , Boris Brezillon References: <20260528093437.2519248-1-hch@lst.de> <20260528093437.2519248-2-hch@lst.de> <5f7f90d8-cb32-4ffb-8f1c-0722aafbe869@kernel.org> <20260529135045.GA10647@lst.de> <5f3ba603-a6ad-4cf2-9a54-aebc10273c59@kernel.org> <58cc76e7-2348-443d-a989-2a06e61178af@kernel.org> <20260601113831.GA25535@lst.de> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/1/26 13:38, Christoph Hellwig wrote: > On Mon, Jun 01, 2026 at 10:16:30AM +0200, Vlastimil Babka (SUSE) wrote: >> > kmem_cache_alloc_bulk() returning 0 was considered a success in that case. >> > >> > Either fixing kmem_cache_alloc_bulk() (and the comment) or fixing the >> > user sounds fine to me. >> >> Would it be wrong if we just returned true for size of 0? Would something >> else break? > > I don't think it is wrong per se, but it feels like the wrong kind of > API. I.e. I don't think the MSM caller actually wants this, as they'd > also do a zero-sized kvmalloc. If p->count is 0 then indeed there's a zero-sized kvmalloc so p->pages == ZERO_SIZE_PTR but then nothing breaks because nothing tries to dereference it? msm_iommu_pagetable_prealloc_cleanup() has a "if (p->count > 0)" branch so it seems it's considered possible. But then the rest of the functions also seems working fine, i.e. kmem_cache_free_bulk() of zero size does nothing, kvfree() of ZERO_SIZE_PTR does nothing. It seems to me kmem_cache_alloc_bulk() returning true for size == 0 fits naturally in this world and is less likely to result in a gotcha?