svn commit: r269963 - head/sys/kern

[Xin Li]

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On 08/14/14 15:47, Alan Cox wrote:
> On 08/14/2014 01:24, Xin Li wrote:
>> On 8/13/14 10:35 PM, John-Mark Gurney wrote:
>>> Xin LI wrote this message on Thu, Aug 14, 2014 at 05:13 +0000:
>>>> Author: delphij Date: Thu Aug 14 05:13:24 2014 New Revision: 
>>>> 269963 URL: http://svnweb.freebsd.org/changeset/base/269963
>>>> 
>>>> Log: Re-instate UMA cached backend for 4K - 64K allocations.
>>>> New consumers like geli(4) uses malloc(9) to allocate
>>>> temporary buffers that gets free'ed shortly, causing frequent
>>>> TLB shootdown as observed in hwpmc supported flame graph.
>> 
>>> Can we do even larger, like 128k for phys io sized blocks?
>> 
>> Sure (Actually I'm running with 128k and 256k buckets enabled on
>> my own storage box; with r269964 we can easily add new buckets
>> without actually activating them by default).
>> 
>> However, I'm relented to add them right now because the current 
>> malloc(9) implementation would use the next bucket size, which is
>> 2x of the previous one, when the requested size is only a little
>> bit larger than the smaller chunk's size.  In real world the
>> larger bucket could eat more memory than all smaller but greater
>> than page-sized bucket combined (the actual consumption is still
>> small, though).
>> 
> 
> The current code already supports sizes that are not powers of 2.
> For example, with
> 
> Index: kern/kern_malloc.c 
> ===================================================================
>
> 
- --- kern/kern_malloc.c  (revision 269997)
> +++ kern/kern_malloc.c  (working copy) @@ -152,8 +152,11 @@ struct
> { {2048, "2048", }, {4096, "4096", }, {8192, "8192", }, +
> {12228, "12228", }, {16384, "16384", }, +       {24576, "24576",
> }, {32768, "32768", }, +       {49152, "49152", }, {65536, "65536",
> }, {0, NULL}, };

Unrelated to the functionality, but this would break 'vmstat -m' which
assumes power of two allocations...

Cheers,
- -- 
Xin LI <delphij at delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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