svn commit: r367165 - head/sys/fs/tmpfs

[Mateusz Guzik]

On 10/30/20, Konstantin Belousov <kostikbel at gmail.com> wrote:
> On Fri, Oct 30, 2020 at 03:08:32PM +0100, Mateusz Guzik wrote:
>> On 10/30/20, Mateusz Guzik <mjg at freebsd.org> wrote:
>> > Author: mjg
>> > Date: Fri Oct 30 14:07:25 2020
>> > New Revision: 367165
>> > URL: https://svnweb.freebsd.org/changeset/base/367165
>> >
>> > Log:
>> >   tmpfs: change tmpfs dirent zone into a malloc type
>> >
>> >   It is 64 bytes.
>> >
>>
>> Right now malloc has only power-of-2 zones but I'm looking into
>> changing that. The allocator itself trivially extends to multiply of
>> 16, but stat collection needs reworking.
>
> Either commit message or follow-up do not explain why stopping using
> zone for dirents is useful.  Intuition says exactly reverse, dirents
> on tmpfs are allocation-intensive typically.
>

Off hand the only reasons to use a dedicated zones that I see are:
- use of any of the routines on object creation/destruction
- non-standard flags like NOFREE
- SMR
- high expected allocated count with sizes poorly fit for malloc

Since malloc itself is implemented on top of zones, the difference
before/after the patch is that now it can re-use the pre-existing 64
byte buckets instead of creating its own copy.

The above follow up was to address potential comments about the size
changing from 64 -- with better malloc granularity this wont be a big
deal. Also note tmpfs already uses malloc to store names.

If anything in my opinion the kernel has unnecessary zones (like the
vnode poll one I patched prior to this).

-- 
Mateusz Guzik <mjguzik gmail.com>