Can we decide between lookasidelist or kmem cache for abd allocations

[datacore-PankajSharma]

hey folks from this PR #80 I can see that lookasidelist cache improved performance on windows for abd allocation, but this works good as long as I have enough ram in the system ( more than 32gb just a round figure). In system with small ram (less than 32). Kmem cache handles it well because of its layered structure. Since lookasidelist cache allocates from freelist and it is just one layer above the os allocator if alloc from lookaside fails it will not be handled properly because we do not have flag like KM_Sleep.

I just wanted to ask can we have physical memory check so that system above 32gb ram uses lookaside list and less than that uses kmem cache. Just a food for thought, I am not sure what will be the repercussions of this.

[lundman]

kmem comes from Solaris/OmniOS and is well tuned for that OS, so it would be curious if one could enhance kmem to be a bit more Windowsy, perhaps by using lookasidellist first, for the static-length allocations (kmem_cache_alloc and friends). Putting some work one layer lower (spl) instead of ZFS's abd_os.c ..