From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (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 A129312E1EF for ; Tue, 23 Apr 2024 12:38:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713875926; cv=none; b=bWJsq94zU/n6q6sla4Mu3LOaX8egwKhb/9o02MS084hvoiPRXNBskBQo+t8FLNkFlLLl0yFKL9x4FGsvDA09ha1H/C5qY2rDSLNhKWHcTq9IHNGNbFXxVeXK7nN+tZ0+u2E6tBaej072hgy27aml1rldxrXgeH2C8/RuNrmthMU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713875926; c=relaxed/simple; bh=VEivHfRBE5PagdBkYDmej9luvUWSDrVWwBvEwkxb/J4=; h=Message-ID:Subject:Date:From:To:Cc:References:In-Reply-To: Content-Type; b=p0vUz613VpqCz105qCt7DZGaFKL01LMZ5I8P41UfNSmu9tcI8aa76Xd4/GPOtlIiIJkN2PaeEgcRNMtbfQyHLxRd6qOnK6skjpKN7FNWK/stgcNa0Fx53uJkcR4OBjPc62XDdN4KgWpcFuNPR0U6RH/+1fP1QLqB9iy6p/NfeUc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=mJvLaQiw; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="mJvLaQiw" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1713875919; h=Message-ID:Subject:Date:From:To:Content-Type; bh=IMcT9AbhGnJybY+mmUrN8SjqJH5jnYogREWe+tzfovQ=; b=mJvLaQiw0B67cWBeIRObCAmlyCIUFJ7lupFAP+PgZry3FcdUNcpEoT1JQRh+L0ucNmg0lduvaPAkkdLwT9b00Wof+PhAZ0Fr3qOh8yws2oBMk7gRDfGy8WMcSCndnSYWXnyec9YghGgI5pt4hWwPmZEAOfmHya6QQ6Yr2uAALKI= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R431e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=xuanzhuo@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0W59BIl._1713875917; Received: from localhost(mailfrom:xuanzhuo@linux.alibaba.com fp:SMTPD_---0W59BIl._1713875917) by smtp.aliyun-inc.com; Tue, 23 Apr 2024 20:38:38 +0800 Message-ID: <1713875473.8690095-1-xuanzhuo@linux.alibaba.com> Subject: Re: [PATCH vhost v2 4/7] virtio_net: big mode support premapped Date: Tue, 23 Apr 2024 20:31:13 +0800 From: Xuan Zhuo To: Jason Wang Cc: virtualization@lists.linux.dev, "Michael S. Tsirkin" , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org References: <20240422072408.126821-1-xuanzhuo@linux.alibaba.com> <20240422072408.126821-5-xuanzhuo@linux.alibaba.com> In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: On Tue, 23 Apr 2024 12:36:42 +0800, Jason Wang wrote: > On Mon, Apr 22, 2024 at 3:24=E2=80=AFPM Xuan Zhuo wrote: > > > > In big mode, pre-mapping DMA is beneficial because if the pages are not > > used, we can reuse them without needing to unmap and remap. > > > > We require space to store the DMA address. I use the page.dma_addr to > > store the DMA address from the pp structure inside the page. > > > > Every page retrieved from get_a_page() is mapped, and its DMA address is > > stored in page.dma_addr. When a page is returned to the chain, we check > > the DMA status; if it is not mapped (potentially having been unmapped), > > we remap it before returning it to the chain. > > > > Based on the following points, we do not use page pool to manage these > > pages: > > > > 1. virtio-net uses the DMA APIs wrapped by virtio core. Therefore, > > we can only prevent the page pool from performing DMA operations, and > > let the driver perform DMA operations on the allocated pages. > > 2. But when the page pool releases the page, we have no chance to > > execute dma unmap. > > 3. A solution to #2 is to execute dma unmap every time before putting > > the page back to the page pool. (This is actually a waste, we don't > > execute unmap so frequently.) > > 4. But there is another problem, we still need to use page.dma_addr to > > save the dma address. Using page.dma_addr while using page pool is > > unsafe behavior. > > > > More: > > https://lore.kernel.org/all/CACGkMEu=3DAok9z2imB_c5qVuujSh=3Dvjj1kx= 12fy9N7hqyi+M5Ow@mail.gmail.com/ > > > > Signed-off-by: Xuan Zhuo > > --- > > drivers/net/virtio_net.c | 123 ++++++++++++++++++++++++++++++++++----- > > 1 file changed, 108 insertions(+), 15 deletions(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index 2c7a67ad4789..d4f5e65b247e 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -439,6 +439,81 @@ skb_vnet_common_hdr(struct sk_buff *skb) > > return (struct virtio_net_common_hdr *)skb->cb; > > } > > > > +static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 l= en) > > +{ > > + sg->dma_address =3D addr; > > + sg->length =3D len; > > +} > > + > > +/* For pages submitted to the ring, we need to record its dma for unma= p. > > + * Here, we use the page.dma_addr and page.pp_magic to store the dma > > + * address. > > + */ > > +static void page_chain_set_dma(struct page *p, dma_addr_t addr) > > +{ > > + if (sizeof(dma_addr_t) > sizeof(unsigned long)) { > > Need a macro like PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA. > > > + p->dma_addr =3D lower_32_bits(addr); > > + p->pp_magic =3D upper_32_bits(addr); > > And this uses three fields on page_pool which I'm not sure the other > maintainers are happy with. For example, re-using pp_maing might be > dangerous. See c07aea3ef4d40 ("mm: add a signature in struct page"). > > I think a more safe way is to reuse page pool, for example introducing > a new flag with dma callbacks? If we use page pool, how can we chain the pages allocated for a packet? Yon know the "private" can not be used. If the pp struct inside the page is not safe, how about: struct { /* Page cache and anonymous pages */ /** * @lru: Pageout list, eg. active_list protected by * lruvec->lru_lock. Sometimes used as a generic list * by the page owner. */ union { struct list_head lru; /* Or, for the Unevictable "LRU list" slot */ struct { /* Always even, to negate PageTail */ void *__filler; /* Count page's or folio's mlocks */ unsigned int mlock_count; }; /* Or, free page */ struct list_head buddy_list; struct list_head pcp_list; }; /* See page-flags.h for PAGE_MAPPING_FLAGS */ struct address_space *mapping; union { pgoff_t index; /* Our offset within mapping. */ unsigned long share; /* share count for fsdax */ }; /** * @private: Mapping-private opaque data. * Usually used for buffer_heads if PagePrivate. * Used for swp_entry_t if PageSwapCache. * Indicates order in the buddy system if PageBuddy. */ unsigned long private; }; Or, we can map the private space of the page as a new structure. Thanks. > > Thanks >