[dns-operations] Truncation query

[Florian Weimer]

On 03/17/2017 07:25 PM, Tony Finch wrote:
> Florian Weimer <fweimer at redhat.com> wrote:
>>
>> I"m going to use MSG_PEEK and MSG_TRUNC to get an accurate size from the
>> kernel and allocate a suitable sized buffer using malloc.  But that's probably
>> not a good choice for high-performance servers.
>
> Is there any reason not to allocate a 64KB buffer when the resolver
> context is initialized, and let the kernel donate pages to the buffer
> if/when that becomes necessary?

Every thread in the system currently has its own resolver context, 
whether or not it currently uses the resolver.  Adding a persistent 64 
KiB buffer to that (and thus to every thread) doesn't seem such a great 
idea.  On 32-bit systems it would even break quite a few applications 
because they are already tuned to be closed to the address space limit. 
(Not that I personally care much about 32-bit anymore, but actively 
breaking backwards compatibility seems a bit much.)

Florian