From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) (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 D02966D1A9; Mon, 8 Apr 2024 13:39:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712583557; cv=none; b=lOWWyRacAZD1qi8L5m6rGZQEN9XOmfx7BRv/Mxg6XC6qOosG1R2hZIyxhtl+F9nSrQze8d2w3CDewRlKs7Yu7GF7SGAyqOtt+z2V0MFgvF5JdRS7a5PRTLLfhEQslzLo7Yob8hPi5M25i+w1oLfcWK5dA8OUhfdWC1uAoAwTPQQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712583557; c=relaxed/simple; bh=oI31ZN7653Zpm2X/5BYpChfstj63prSTMYTZKZz+H/I=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=erHDU+mEHys7OYqyFz+BYOxaEU4aLDWoTfatyxWjxKtCx+46Gd1Ig6VzxCMLXs1Dib6YtbfRKbm6EDfxnEzu7UK2Ku+jmZaPn4pxT0XhaXPmOVMt91TibKKWDgmqh2sVjggjcgDj8e5tVATePZ8QgdSUNSdTZdR1URYUXt6jsD4= 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=45.249.212.189 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 [172.19.163.174]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4VCqrN74T4zNmxt; Mon, 8 Apr 2024 21:36:52 +0800 (CST) Received: from dggpemm500005.china.huawei.com (unknown [7.185.36.74]) by mail.maildlp.com (Postfix) with ESMTPS id 1616B140134; Mon, 8 Apr 2024 21:39:07 +0800 (CST) Received: from [10.69.30.204] (10.69.30.204) by dggpemm500005.china.huawei.com (7.185.36.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.35; Mon, 8 Apr 2024 21:39:06 +0800 Subject: Re: [PATCH net-next v1 02/12] mm: page_frag: use initial zero offset for page_frag_alloc_align() To: Alexander H Duyck , , , CC: , , Andrew Morton , References: <20240407130850.19625-1-linyunsheng@huawei.com> <20240407130850.19625-3-linyunsheng@huawei.com> <43d99616cd4a2a6fce6a6b97f73d08ebc5361a61.camel@gmail.com> From: Yunsheng Lin Message-ID: Date: Mon, 8 Apr 2024 21:39:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <43d99616cd4a2a6fce6a6b97f73d08ebc5361a61.camel@gmail.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemm500005.china.huawei.com (7.185.36.74) On 2024/4/8 1:52, Alexander H Duyck wrote: > On Sun, 2024-04-07 at 21:08 +0800, Yunsheng Lin wrote: >> We are above to use page_frag_alloc_*() API to not just >> allocate memory for skb->data, but also use them to do >> the memory allocation for skb frag too. Currently the >> implementation of page_frag in mm subsystem is running >> the offset as a countdown rather than count-up value, >> there may have several advantages to that as mentioned >> in [1], but it may have some disadvantages, for example, >> it may disable skb frag coaleasing and more correct cache >> prefetching >> >> We have a trade-off to make in order to have a unified >> implementation and API for page_frag, so use a initial zero >> offset in this patch, and the following patch will try to >> make some optimization to aovid the disadvantages as much >> as possible. >> >> 1. https://lore.kernel.org/all/f4abe71b3439b39d17a6fb2d410180f367cadf5c.camel@gmail.com/ >> >> CC: Alexander Duyck >> Signed-off-by: Yunsheng Lin >> --- >> mm/page_frag_cache.c | 31 ++++++++++++++----------------- >> 1 file changed, 14 insertions(+), 17 deletions(-) >> >> diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c >> index a0f90ba25200..3e3e88d9af90 100644 >> --- a/mm/page_frag_cache.c >> +++ b/mm/page_frag_cache.c >> @@ -67,9 +67,8 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, >> unsigned int fragsz, gfp_t gfp_mask, >> unsigned int align_mask) >> { >> - unsigned int size = PAGE_SIZE; >> + unsigned int size, offset; >> struct page *page; >> - int offset; >> >> if (unlikely(!nc->va)) { >> refill: >> @@ -77,10 +76,6 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, >> if (!page) >> return NULL; >> >> -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) >> - /* if size can vary use size else just use PAGE_SIZE */ >> - size = nc->size; >> -#endif >> /* Even if we own the page, we do not use atomic_set(). >> * This would break get_page_unless_zero() users. >> */ >> @@ -89,11 +84,18 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, >> /* reset page count bias and offset to start of new frag */ >> nc->pfmemalloc = page_is_pfmemalloc(page); >> nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; >> - nc->offset = size; >> + nc->offset = 0; >> } >> >> - offset = nc->offset - fragsz; >> - if (unlikely(offset < 0)) { >> +#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) >> + /* if size can vary use size else just use PAGE_SIZE */ >> + size = nc->size; >> +#else >> + size = PAGE_SIZE; >> +#endif >> + >> + offset = ALIGN(nc->offset, -align_mask); >> + if (unlikely(offset + fragsz > size)) { > > Rather than using "ALIGN" with a negative value it would probably make > more sense to use __ALIGN_KERNEL_MASK with ~align_mask. I am not sure > how well the compiler sorts out the use of negatives to flip values > that are then converted to masks with the "(a) - 1". The next patch will remove the '-' in '-align_mask' as the 'ALIGN' operation is done in the inline helper. I am not sure that matter much to use __ALIGN_KERNEL_MASK with ~align_mask? >