On 10/30/20, Mark Johnston <ma...@freebsd.org> wrote:
> On Fri, Oct 30, 2020 at 03:08:32PM +0100, Mateusz Guzik wrote:
>> On 10/30/20, Mateusz Guzik <m...@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.
>
> Sums of consecutive powers of 2 also works well. That is, 16, 16 + 8,
> 32, 32 + 16, ...
>
> When I last looked I didn't see very many places that would benefit, at
> least outside of ZFS. Probably the main one is CAM CCBs, and that'll be
> helped by https://reviews.freebsd.org/D26844 .
>
I collected stats over part of make tinderbox, where they are rounded
up to mulitplies of 8. (so size of 5 is 1, size of 32 is 4). There is
huge demand for non-power-of-2 and a multiply of 16 is a conservative
adjustment which wont require more than a few workloads to compare
before/after.
For example you can see a solid contingent of 9 (72 bytes) which right
now is served from 128 byte zones.
dtrace -n 'fbt::malloc:entry { @ = lquantize(arg0 % 8 ? ((arg0 / 8) *
8 + 1) : arg0 / 8, 0, 32, 1); }'
value ------------- Distribution ------------- count
0 | 0
1 | 292436
2 | 140962
3 | 322732
4 |@@@@@ 12150230
5 | 686069
6 | 41067
7 |@ 2847728
8 |@@@ 6449825
9 |@@ 5794112
10 | 1107100
11 | 5913
12 | 15392
13 | 21885
14 | 1852
15 | 4100
16 | 5177
17 |@ 1833685
18 | 1541
19 | 1567
20 | 1189
21 | 809
22 | 7294
23 | 423
24 | 355
25 | 364280
26 | 450
27 | 416
28 | 444
29 | 193
30 | 83
31 | 188
>= 32 |@@@@@@@@@@@@@@@@@@@@@@@@@@ 61740786
--
Mateusz Guzik <mjguzik gmail.com>
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