Re: Fix bank selection logic in SLRU

19.12.2024 13:10, Andrey Borodin пишет:
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>
>> On 19 Dec 2024, at 15:01, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru> wrote:
>>
>> - `&` takes 0.69ns
>> - `mult-rec` takes 2.94ns
>> - `%` takes 3.24ns.
>
> Thanks, Yura, for benchmarks and off-list conversation.
> I’ve reproduced similar numbers on my Apple M2.
> I agree that additional 3-4ns are negligible in case of SLRU access.
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>
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> + bits16 nbanks;
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> Perhaps, it’s not bits anymore. Also, is 64K banks ought enough for everybody?
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>
> Best regards, Andrey Borodin.

There are artificial limit currently:

#define SLRU_MAX_ALLOWED_BUFFERS ((1024 * 1024 * 1024) / BLCKSZ)
#define SLRU_BANK_BITSHIFT 4
#define SLRU_BANK_SIZE (1 << SLRU_BANK_BITSHIFT)

So, there's no more than 8192 banks at the moment.

But I believe, some customers will want to have more than 1GB of SLRU in
the future. (They do already actually)

----
Yura