Re: [PATCH] mm: add zblock allocator

[igor.b@beldev.am]

Hi Shakeel,

2025-04-02 03:16 Shakeel Butt wrote:
> Hi Vitaly,
> 
> On Tue, Apr 01, 2025 at 07:17:54PM +0200, Vitaly Wool wrote:
>> zblock is a special purpose allocator for storing compressed pages.
>> It stores integer number of compressed objects per its block. These
>> blocks consist of several physical pages (2**n, i. e. 1/2/4/8).
>> 
>> With zblock, it is possible to densely arrange objects of various 
>> sizes
>> resulting in low internal fragmentation. Also this allocator tries to
>> fill incomplete blocks instead of adding new ones,  in many cases
>> providing a compression ratio substantially higher than z3fold and 
>> zbud
>> (though lower than zmalloc's).
>> 
>> zblock does not require MMU
> 
> Can you explain why not requiring MMU is important for your use-case?
> Also what exactly is your use-case? Are you planning to use zblock
> through zram or zswap or something new?

We have 2 use cases for a zpool backend: data centers (zswap) and small 
MMU less devices, this is where zram comes ito play. We know that zram 
over zpool patch is still out of tree but we also know the story behind 
that :)

>> to operate and also is superior to zsmalloc
>> with regard to average performance and worst execution times, thus
>> allowing for better response time and real-time characteristics of the
>> whole system.
>> 
>> E. g. on a series of stress-ng tests run on a Raspberry Pi 5, we get
>> 5-10% higher value for bogo ops/s in zblock/zsmalloc comparison.
> 
> Can you explain a bit more on this test? How is this test using zblock?

We're running stress-ng on a number of devices. The results published in 
the previous message are from the run on Raspberry Pi 5. zpool's 
settings used for comparison are lz4/80%.

Thanks,
Igor