From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) (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 196F9568A for ; Wed, 24 Apr 2024 01:09:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.130 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713920992; cv=none; b=DsKpYC+lzdQ9wRbhD0p+ym93wxt0+p4ScvjypHbFQdn7ca9aBTy9cwjc4P5kLQ8iVATemV/WS/HgNSdjxbyKCJE6Jiz9wrpTfcxnU3LERDrfnrcHvkhcOLpFa2qqvI5WgiauDVqakcd96Q+cHLR6hUgyibGl5xkDLKigQzZ/Rlg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713920992; c=relaxed/simple; bh=i4VC88NMsw0kRrws/BpaVN2NQ2hM2dWJeu/nn+ZOy0s=; h=Message-ID:Subject:Date:From:To:Cc:References:In-Reply-To: Content-Type; b=nI+y2sRn3u73lrlmEcH5EDzo0PIIfDXMVLa+3mZYA7+3In+0uoRUTOkYdklx0ffjGW4pvzVSXgapLzMbP4ThvXgb46Q2WSCzaQiJ+/nju53nrJDwxQOX+njHEh2X1N6ZbWQpS24V6IN/x2JeDt/U8FagyVo/McUVCvoPyejL5Ng= 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=VP78RmlD; arc=none smtp.client-ip=115.124.30.130 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="VP78RmlD" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1713920986; h=Message-ID:Subject:Date:From:To:Content-Type; bh=GCZOyXnsBavAtLpXf1Crt3mG5AmPXtFHZ00VZxSsq5M=; b=VP78RmlDm1mSdip/8LEYIS7n8/zVOii0aG3wzajl9aa650noWphGCGuB7+yeuF5d6GPBUuNO4Qk9+u5NghppFUWKCH8FZBOq7H/f8EZaSaNSCKjNVOd0s/K/s2OwEaEHmkNH8eHYf0hLVlljLZ1Ae4zB0XJeeGFfwx9k9dkmv/o= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R751e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037067113;MF=xuanzhuo@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0W5ARj6O_1713920984; Received: from localhost(mailfrom:xuanzhuo@linux.alibaba.com fp:SMTPD_---0W5ARj6O_1713920984) by smtp.aliyun-inc.com; Wed, 24 Apr 2024 09:09:46 +0800 Message-ID: <1713919985.3490202-1-xuanzhuo@linux.alibaba.com> Subject: Re: [PATCH vhost v2 4/7] virtio_net: big mode support premapped Date: Wed, 24 Apr 2024 08:53:05 +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> <1713875473.8690095-1-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 Wed, 24 Apr 2024 08:43:21 +0800, Jason Wang wrote: > On Tue, Apr 23, 2024 at 8:38=E2=80=AFPM Xuan Zhuo wrote: > > > > On Tue, 23 Apr 2024 12:36:42 +0800, Jason Wang wr= ote: > > > 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 addre= ss is > > > > stored in page.dma_addr. When a page is returned to the chain, we c= heck > > > > the DMA status; if it is not mapped (potentially having been unmapp= ed), > > > > we remap it before returning it to the chain. > > > > > > > > Based on the following points, we do not use page pool to manage th= ese > > > > 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 putti= ng > > > > the page back to the page pool. (This is actually a waste, we do= n'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=3Dvj= j1kx12fy9N7hqyi+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, u= 32 len) > > > > +{ > > > > + sg->dma_address =3D addr; > > > > + sg->length =3D len; > > > > +} > > > > + > > > > +/* For pages submitted to the ring, we need to record its dma for = unmap. > > > > + * Here, we use the page.dma_addr and page.pp_magic to store the d= ma > > > > + * 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? > > I'm not sure I get this, it is chained via the descriptor flag. In the big mode, we will commit many pages to the virtio core by virtqueue_add_inbuf(). By virtqueue_get_buf_ctx(), we got the data. That is the first page. Other pages are chained by the "private". If we use the page pool, how can we chain the pages. After virtqueue_add_inbuf(), we need to get the pages to fill the skb. > > > > > 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 protecte= d by > > * lruvec->lru_lock. Sometimes used as a gener= ic list > > * by the page owner. > > */ > > union { > > struct list_head lru; > > > > /* Or, for the Unevictable "LRU list" s= lot */ > > struct { > > /* Always even, to negate PageT= ail */ > > void *__filler; > > /* Count page's or folio's mloc= ks */ > > 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 w= ithin 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 PageB= uddy. > > */ > > unsigned long private; > > }; > > > > Or, we can map the private space of the page as a new structure. > > It could be a way. But such allocation might be huge if we are using > indirect descriptors or I may miss something. No. we only need to store the "chain next" and the dma as this patch set di= d. The size of the private space inside the page is 20(32bit)/40(64bit) bytes. That is enough for us. If you worry about the change of the pp structure, we can use the "private"= as origin and use the "struct list_head lru" to store the dma. The min size of "struct list_head lru" is 8 bytes, that is enough for the dma_addr_t. We can do this more simper: static void page_chain_set_dma(struct page *p, dma_addr_t dma) { BUILD_BUG_ON(sizeof(p->lru)) < sizeof(dma)); dma_addr_t *addr; addr =3D &page->lru; *addr =3D dma; } Thanks. > > Thanks > > > > > Thanks. > > > > > > > > > > Thanks > > > > > >