Re: Fix bank selection logic in SLRU

On Tue, 10 Dec 2024 at 7:30 PM, Robert Haas <robertmhaas@gmail.com> wrote:

> On Tue, Dec 10, 2024 at 8:58 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >> Bank selection code assumes that number of buffers is power of 2.
> >> If the number of buffers is not power of 2 - only subset of buffers
> will be used. In worst case, e.g. 65 buffers, everything will be buffered
> only in bank 64.
> >
> > But why that would be the case? the acceptable values for GUC to
> configure the slru buffers are in multiple of 16(bank size) we have that
> check to check the GUC values.
>
> "Must be a multiple of 16" and "must be a power of 2" are different
> criteria. For example, 48 is a multiple of 16 but it is not a power of
> 2. If the code assumes that we have an actual power of 2, the check
> you quoted in your previous email is insufficient.


Yeah I see it’s an issue.  Thanks for clarifying.

—
Dilip

>