Re: kern/57558: pgdaemon 100% busy - no scanning (ZFS case)

[Frank Kardel <kardel%netbsd.org@localhost>]

On 05/09/24 19:48, Chuck Silvers wrote:

> great, thanks for testing.
>
> which other cases are you talking about?
>
> -Chuck

The cases in the KVA nkmempages determination.

#if defined(NKMEMPAGES_MAX_UNLIMITED) && !defined(KMSAN)
        /*
         * The extra 1/9 here is to account for uvm_km_va_starved_p()
         * wanting to keep 10% of kmem virtual space free.
         * The intent is that on "unlimited" platforms we should be able
         * to allocate all of physical memory as kmem without running short
         * of kmem virtual space.
         */
        npages = (physmem * 10) / 9;
#else

#if defined(KMSAN)
        npages = (physmem / 4);
#elif defined(PMAP_MAP_POOLPAGE)
        npages = (physmem / 4);
#else
        npages = (physmem / 3) * 2;
#endif /* defined(PMAP_MAP_POOLPAGE) */

#if !defined(NKMEMPAGES_MAX_UNLIMITED)
        if (npages > NKMEMPAGES_MAX)
                npages = NKMEMPAGES_MAX;
#endif

#endif

        if (npages < NKMEMPAGES_MIN)
                npages = NKMEMPAGES_MIN;

        nkmempages = npages;

defined(NKMEMPAGES_MAX_UNLIMITED) && !defined(KMSAN) is running fine now.

I wonder whether we could hit the starvation scenario where ZFS does not 
reclaim memory in time in

the other cases as there nkmempages is set to a value less than physmem.

Just wondering.

-Frank