lkml.org 
[lkml]   [2022]   [Jun]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe:Re: [PATCH v2] net: ethernet: mtk_eth_soc: fix misuse of mem alloc interface netdev[napi]_alloc_frag
At 2022-06-03 23:33:25, "Alexander Duyck" <alexander.duyck@gmail.com> wrote:
>On Fri, Jun 3, 2022 at 8:25 AM Alexander Duyck
><alexander.duyck@gmail.com> wrote:
>>
>> On Fri, Jun 3, 2022 at 2:03 AM Chen Lin <chen45464546@163.com> wrote:
>> >
>> > When rx_flag == MTK_RX_FLAGS_HWLRO,
>> > rx_data_len = MTK_MAX_LRO_RX_LENGTH(4096 * 3) > PAGE_SIZE.
>> > netdev_alloc_frag is for alloction of page fragment only.
>> > Reference to other drivers and Documentation/vm/page_frags.rst
>> >
>> > Branch to use alloc_pages when ring->frag_size > PAGE_SIZE.
>> >
>> > Signed-off-by: Chen Lin <chen45464546@163.com>
>> > ---
>> > drivers/net/ethernet/mediatek/mtk_eth_soc.c | 22 ++++++++++++++++++++--
>> > 1 file changed, 20 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
>> > index b3b3c07..772d903 100644
>> > --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
>> > +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
>> > @@ -1467,7 +1467,16 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>> > goto release_desc;
>> >
>> > /* alloc new buffer */
>> > - new_data = napi_alloc_frag(ring->frag_size);
>> > + if (ring->frag_size <= PAGE_SIZE) {
>> > + new_data = napi_alloc_frag(ring->frag_size);
>> > + } else {
>> > + struct page *page;
>> > + unsigned int order = get_order(ring->frag_size);
>> > +
>> > + page = alloc_pages(GFP_ATOMIC | __GFP_COMP |
>> > + __GFP_NOWARN, order);
>> > + new_data = page ? page_address(page) : NULL;
>> > + }
>> > if (unlikely(!new_data)) {
>> > netdev->stats.rx_dropped++;
>> > goto release_desc;
>> > @@ -1914,7 +1923,16 @@ static int mtk_rx_alloc(struct mtk_eth *eth, int ring_no, int rx_flag)
>> > return -ENOMEM;
>> >
>> > for (i = 0; i < rx_dma_size; i++) {
>> > - ring->data[i] = netdev_alloc_frag(ring->frag_size);
>> > + if (ring->frag_size <= PAGE_SIZE) {
>> > + ring->data[i] = netdev_alloc_frag(ring->frag_size);
>> > + } else {
>> > + struct page *page;
>> > + unsigned int order = get_order(ring->frag_size);
>> > +
>> > + page = alloc_pages(GFP_KERNEL | __GFP_COMP |
>> > + __GFP_NOWARN, order);
>> > + ring->data[i] = page ? page_address(page) : NULL;
>> > + }
>> > if (!ring->data[i])
>> > return -ENOMEM;
>> > }
>>
>> Actually I looked closer at this driver. Is it able to receive frames
>> larger than 2K? If not there isn't any point in this change.
>>
>> Based on commit 4fd59792097a ("net: ethernet: mediatek: support
>> setting MTU") it looks like it doesn't, so odds are this patch is not
>> necessary.
>
>I spoke too soon. I had overlooked the LRO part. With that being the
>case you can probably optimize this code to do away with the get_order
>piece entirely, at least during runtime. My main concern is that doing
>that in the fast-path will be expensive so you would be much better
>off doing something like
>get_order(mtk_max_frag_size(MTK_RX_FLAGS_HWLRO)) which would be
>converted into a constant at compile time since everything else would
>be less than 1 page in size.
>
>Also you could then replace alloc_pages with __get_free_pages which
>would take care of the page_address call for you.

Thanks for the tips. I'll try again.
It can also be seen from here it is easy to make mistakes in parameter fragsz.
\
 
 \ /
  Last update: 2022-06-05 04:24    [W:1.134 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site