Matthew Dillon <[email protected]> wrote: > > :Hm, I understand if hammer cleanup removes other data from cache, but > :why should the disk cache usage push out data to swap? > :I just tried a hammer cleanup on a completely idle system with 1.5G > :memory in single user mode, and during the reblocking it started to > :use swap and became unresponsive - is this really working as expected? > : > :Cheers, > :Johannes > > You couldn't ^C the reblock? Reblocking works the storage system > pretty heavily, performance issues are not necessarily going to be > related to paging activity. Anything which has to read from disk will > be slow. > > How does the system know what pages are idle and what pages are not > idle when the whole system is idle? How can the system distinguish > between the one-time scan that the reblocker does verses, say, someone > rdist'ing a dataset which would easily fit in memory that we DO want > to cache?
^C did succeed, but it took quite long - no lockup though. It's understood, that all disk IO will be slow. I was just surprised that the system uses swap in this case at all. Why should the system move data out to swap to make place for the disk cache - at least if swap does not happen to be on SSD? I would have thought that only memory not otherwise needed is used to cache disk data. I will retry with swap disabled completely. Johannes
