questions from FreeBSD user

Wojciech Puchar wojtek at
Sun Jul 15 23:08:21 PDT 2012

>    though I don't remember the exact reason I chose it originally.
>    The practical limitation for swap is 4096GB (4TB) due to the use
>    of 32 bit block numbers coupled with internal arithmatic overflows
>    in the swap algorithms which eats another 2 bits.

this is definitely enough for me :)

>    We do not want to increase the size of the radix tree element because
>    the larger structure size would double the per-swap-block physical memory
>    overhead, and physical memory overhead is already fairly significant...
>    around  1MB of physical memory is needed per 1GB of swap.

this is right. i don't like more locked memory just because more swap may 
POSSIBLY be used.

>    There are a maximum of 4 swap devices (w/512GB limit by default in total,
>    with the per-device limit 1/4 of that).  Devices are automatically

too - it is enough.

For now i am FreeBSD user, but when i read what are proposed by 
developers(!) for FreeBSD i clearly understand i will need something else.

And swapcache is nearly what i need for one use where i have a mix of I/O 
heavy files and large data. dividing it manually is hard.

>    UFS ought to be be cached by swapcache but there's no point using it
>    on DragonFly.  You should use HAMMER.

do you wrote some (even rough and preliminary) about how hammer's data is 
laid out over disk? Or maybe better HAMMER2 which you are working on now.

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