Messages in this thread | | | Date | Fri, 20 Nov 1998 13:09:48 +0100 | From | "Dr. Werner Fink" <> | Subject | Re: Linux-2.1.129.. |
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On Thu, Nov 19, 1998 at 10:58:30PM +0100, Rik van Riel wrote: > On Thu, 19 Nov 1998, Dr. Werner Fink wrote: > > > Yes on a 512MB system it's a great win ... on a 64 system I see > > something like a ``swapping weasel'' under high load. > > > > It seems that page ageing or something *similar* would be nice > > for a factor 512/64 >= 2 ... under high load and not enough > > memory it's maybe better if we could get the processes in turn > > into work instead of useless swapping (this was a side effect > > of page ageing due to the implicit slow down). > > It was certainly a huge win when page aging was implemented, > but we mainly felt that because there used to be an obscure > bug in vmscan.c, causing the kernel to always start scanning > at the start of the process' address space. > > Now that bug is fixed, it might just be better to switch > to a multi-queue system. A full implementation of that > will have to wait until 2.3, but we can easily do an > el-cheapo simulation of it by simply not freeing swap > cached pages on the first pass of shrink_mmap().
Hmmm ... we need something real for 2.2 ... so, let's analyse the problem
If the average time slice of the processes is eaten up by swapping page back *and* if these pages are spapped out during to the next time slice the system becomes unusable (freeing swap cached pages on the first pass of shrink_mmap() does force this behaviour at high stress).
Therefore we need something like a page ageing which does not mean that the old scheme is required.
Pages which are swapped in need a higher life time in physical memory. If a page can be shared this life time could be a bigger one. If a process counts such pages up to a limit his pages should not get a higher life for the next few cycles.
This simple scheme should be implementable in a easy way, shouldn't it? The appropiate places are
ipc/shm.c::shm_swap_in() mm/page_alloc.c::swap_in()
and the old place of the old age_page():
mm/vmscan.c::try_to_swap_out()
together with some unused variables out of
include/linux/sched.h::task_struct (e.g. dec_flt) include/linux/sched.h::struct page (e.g. unused :-)
nothing more is needed due to the better swap cache of 2.1.129 in comparision to 2.0.36.
Werner
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