maximum MAXBSIZE

[Peter Jeremy]

On 2020-Jan-09 16:45:19 +0100, Gary Jennejohn <gljennjohn at gmail.com> wrote:
>On Thu, 9 Jan 2020 15:21:25 +0100 (CET)
>Wojciech Puchar <wojtek at puchar.net> wrote:
>> why FreeBSD default is so completely wrong for modern hardware?
>> 
>> i think 4MB is OK for HDDs, more may be optimal for RAID5 arrays.
>
>POLA (principle of least amazement).  I certainly don't need a MAXPHYS set
>to 4MB on my desktop machine.

What are the downsides of running with MAXPHYS set to 4MB (or similar)?

>  Not everyone using FreeBSD is running
>servers with large amounts of memory and disk storage.

Actually, I disagree with this statement.  MAXPHYS on x86 was doubled from
64KB to 128KB in r32724 - 22 years ago.  A small, embedded system today has
more RAM than a decent server had disk space then.  I think we are well
overdue for an examination of many of the kernel parameters to take into
account that a "typical" user machine today has 3 orders of magnitude more
RAM, disk and performance than it had when most of the kernel parameters
were last tweaked.

>It's a trivial change if it's beneficial in a certain use scenario.  The
>decision should be left up to the user.

Actually, I suspect it would benefit most typical use cases - even an
average desktop machine does for more I/O than when the values were last
set.  Also, adjusting it isn't quite that easy - it's a compile-time
constant so a user has to build their own kernel and the Project is trying
to get away from requiring users to build from source.

And, before someone starts, the "it will hurt embedded systems" argument
isn't a good reason for keeping the status quo for two main reasons:

1) As I mentioned above, an embedded system today is larger than a decent
server was in 1998.

2) People running FreeBSD on embedded systems are going to want to build
from source to cater for their systems' idiosyncracies and needs, so they
can easily tune kernel parameters as needed.

-- 
Peter Jeremy
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