On 02/12/2019 06:04 PM, David Ahern wrote:
> On 2/12/19 6:58 PM, Eric Dumazet wrote:
>> In the past, we tried to increase the buffer size up to 32 KB in order
>> to reduce number of syscalls per dump.
>>
>> Commit 2d34851cd341 ("lib/libnetlink: re malloc buff if size is not enough")
>> brought the size back to 4KB because the kernel can not know the application
>> is ready to receive bigger requests.
>>
>> See kernel commits 9063e21fb026 ("netlink: autosize skb lengthes") and
>> d35c99ff77ec ("netlink: do not enter direct reclaim from netlink_dump()")
>> for more details.
>>
>> Fixes: 2d34851cd341 ("lib/libnetlink: re malloc buff if size is not enough")
>> Signed-off-by: Eric Dumazet <eduma...@google.com>
>> Cc: Hangbin Liu <liuhang...@gmail.com>
>> Cc: Phil Sutter <p...@nwl.cc>
>> ---
>> lib/libnetlink.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/lib/libnetlink.c b/lib/libnetlink.c
>> index
>> 1892a02ab5d0d73776c9882ffc77edcd2c663d01..0d48a3d43cf03065dacbd419578ab10af56431a4
>> 100644
>> --- a/lib/libnetlink.c
>> +++ b/lib/libnetlink.c
>> @@ -718,6 +718,8 @@ static int rtnl_recvmsg(int fd, struct msghdr *msg, char
>> **answer)
>> if (len < 0)
>> return len;
>>
>> + if (len < 32768)
>> + len = 32768;
>> buf = malloc(len);
>> if (!buf) {
>> fprintf(stderr, "malloc error: not enough buffer\n");
>>
>
> I believe that negates the whole point of 2d34851cd341 - which I have no
> problem with. 2 recvmsg calls per message is overkill.
>
It does not negates the point at all.
The main point was to eventually be able to allocate more than 32KB.
We need to have a minimum size of 32KB so that the kernel can cook reasonably
sized skbs
Because trying to allocate 4KB only in 2019 is kind of stupid...
( Especially considering ss currently buffers the whole thing before calling
render() !!! )
> Do we know of any single message sizes > 32k? 2d34851cd341 cites
> increasing VF's but at some point there is a limit. If not, the whole
> PEEK thing should go away and we just malloc 32k (or 64k) buffers for
> each recvmsg.
>
