From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) (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 199121AC425; Fri, 16 Aug 2024 11:55:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.255 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723809361; cv=none; b=MXRBFwcNh3GQ3BZ2ott7TCXrAIH0MwXwzLiWbgtzkNwdXQP4A3pjIR5ezr+Pd1ACOv5ikDpmTPfVz+QY9KNLHNLYrVZJNDhoOrzIKqi3uGSQsTntrtlRg2v8MT6dDJqWj4r0LRcyGDdAacaP/+nI6WUkolrQSSHkum/8eKYbjp8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723809361; c=relaxed/simple; bh=SVX+wbwMVGyzqZ9Uy2tRkt4Pwr5gXi5w8kw+OpNVwMw=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=jUdWcv1oCU9pJyL0rrEiTfeaBKNQ0zV+Ajw2OzJ8BKa7HvUi5EUDZWcNFUKfDUusC1ahhwZ2Uh1wUxjTPwoh3aue4ngaicwxGwiaWU7FXbeiw5XPn/ciHGgWSWlfQrQs7Tv34KLNqWIzotwE5sVzP/qWJWE1H9iKCkENKdgsEk0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.255 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.105]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4WlgRJ4L9Pz1T7Mq; Fri, 16 Aug 2024 19:55:24 +0800 (CST) Received: from dggpemf200006.china.huawei.com (unknown [7.185.36.61]) by mail.maildlp.com (Postfix) with ESMTPS id 0F51F140137; Fri, 16 Aug 2024 19:55:57 +0800 (CST) Received: from [10.67.120.129] (10.67.120.129) by dggpemf200006.china.huawei.com (7.185.36.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Fri, 16 Aug 2024 19:55:56 +0800 Message-ID: <1a6aab37-2783-45a2-8edd-0990b211ac2d@huawei.com> Date: Fri, 16 Aug 2024 19:55:56 +0800 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 net-next v13 07/14] mm: page_frag: reuse existing space for 'size' and 'pfmemalloc' To: Alexander Duyck CC: , , , , , Andrew Morton , References: <20240808123714.462740-1-linyunsheng@huawei.com> <20240808123714.462740-8-linyunsheng@huawei.com> <0002cde37fcead62813006ab9516c5b2fdbf113a.camel@gmail.com> Content-Language: en-US From: Yunsheng Lin In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemf200006.china.huawei.com (7.185.36.61) On 2024/8/15 23:03, Alexander Duyck wrote: > On Wed, Aug 14, 2024 at 8:10 PM Yunsheng Lin wrote: >> >> On 2024/8/15 0:13, Alexander H Duyck wrote: >>> On Thu, 2024-08-08 at 20:37 +0800, Yunsheng Lin wrote: >>>> Currently there is one 'struct page_frag' for every 'struct >>>> sock' and 'struct task_struct', we are about to replace the >>>> 'struct page_frag' with 'struct page_frag_cache' for them. >>>> Before begin the replacing, we need to ensure the size of >>>> 'struct page_frag_cache' is not bigger than the size of >>>> 'struct page_frag', as there may be tens of thousands of >>>> 'struct sock' and 'struct task_struct' instances in the >>>> system. >>>> >>>> By or'ing the page order & pfmemalloc with lower bits of >>>> 'va' instead of using 'u16' or 'u32' for page size and 'u8' >>>> for pfmemalloc, we are able to avoid 3 or 5 bytes space waste. >>>> And page address & pfmemalloc & order is unchanged for the >>>> same page in the same 'page_frag_cache' instance, it makes >>>> sense to fit them together. >>>> >>>> After this patch, the size of 'struct page_frag_cache' should be >>>> the same as the size of 'struct page_frag'. >>>> >>>> CC: Alexander Duyck >>>> Signed-off-by: Yunsheng Lin >>>> --- >>>> include/linux/mm_types_task.h | 16 +++++----- >>>> include/linux/page_frag_cache.h | 52 +++++++++++++++++++++++++++++++-- >>>> mm/page_frag_cache.c | 49 +++++++++++++++++-------------- >>>> 3 files changed, 85 insertions(+), 32 deletions(-) >>>> >>>> diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h >>>> index b1c54b2b9308..f2610112a642 100644 >>>> --- a/include/linux/mm_types_task.h >>>> +++ b/include/linux/mm_types_task.h >>>> @@ -50,18 +50,18 @@ struct page_frag { >>>> #define PAGE_FRAG_CACHE_MAX_SIZE __ALIGN_MASK(32768, ~PAGE_MASK) >>>> #define PAGE_FRAG_CACHE_MAX_ORDER get_order(PAGE_FRAG_CACHE_MAX_SIZE) >>>> struct page_frag_cache { >>>> - void *va; >>>> -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) >>>> + /* encoded_va consists of the virtual address, pfmemalloc bit and order >>>> + * of a page. >>>> + */ >>>> + unsigned long encoded_va; >>>> + >>> >>> Rather than calling this an "encoded_va" we might want to call this an >>> "encoded_page" as that would be closer to what we are actually working >>> with. We are just using the virtual address as the page pointer instead >>> of the page struct itself since we need quicker access to the virtual >>> address than we do the page struct. >> >> Calling it "encoded_page" seems confusing enough when calling virt_to_page() >> with "encoded_page" when virt_to_page() is expecting a 'va', no? > > It makes about as much sense as calling it an "encoded_va". What you > have is essentially a packed page struct that contains the virtual > address, pfmemalloc flag, and order. So if you want you could call it > "packed_page" too I suppose. Basically this isn't a valid virtual > address it is a page pointer with some extra metadata packed in. I think we are all argeed that is not a valid virtual address by adding the 'encoded_' part. I am not really sure if "encoded_page" or "packed_page" is better than 'encoded_va' here, as there is no 'page pointer' that is implied by "encoded_page" or "packed_page" here. For 'encoded_va', at least there is 'virtual address' that is implied by 'encoded_va', and that 'virtual address' just happen to be page pointer. Yes, you may say the 'pfmemalloc flag and order' part is about page, not about 'va', I guess there is trade-off we need to make here if there is not a perfect name for it and 'va' does occupy most bits of 'encoded_va'.