I am very confused about paging/swapping on TU4.0F (and probably all versions).
I have always assumed that when memory got low the system made use of
swap space by paging out to it, and the documentation seems to indicate this
(quoted below), but I've just watched a system with "eager swap" use up
its physical memory, not touch its 5GB of swap space, and let the process
die. Either our memory parameters are way off on this box or I'm not
understanding what is happening. The system has 1GB of memory, and the job
in question wants to use 179MB of memory. The system had avail. about 160MB
of physical memory at the start of the job, and the job dies when free
physical memory gets down to around 33MB. Swap space, according to
"top", stays at 11MB in use.
Can someone please enlighten me as to what happens, and point me to any
tips on what to do to optimize this system so it uses swap to allow us
to run jobs with insufficient memory. I know, this is not optimal, but
it's a test system, we just need to see the code run at this point,
we'll worry about performance later.
Regards,
Judith Reed
jreed_at_appliedtheory.com
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(Documentation says...)
The paging process is as follows:
1.The page reclamation code activates the page-stealer daemon,
which first reclaims the pages that the UBC has borrowed from the
virtual memory subsystem, until the size of the UBC reaches the
borrowing threshold that is specified by the value of the
ubc-borrowpercent attribute (the default is 20 percent). Freeing borrowed
UBC pages is a fast way to reclaim pages, because UBC pages are usually
not modified. If the reclaimed pages are dirty (modified), their contents
must be written to disk before the pages can be moved to the free page list.
2.If freeing UBC borrowed memory does not sufficiently replenish the
free list, a pageout occurs. The page-stealer daemon reclaims the oldest
inactive and UBC LRU pages from the active page list, moves the contents
of the modified pages to swap space, and puts the clean pages on the free
list.
3.Paging becomes increasingly aggressive if the number of free pages
continues to decrease. If the number of pages on the free page list
falls below the value of the vm subsystem attribute vm-page-free-min
(the default is 20 pages), a page must be reclaimed for each page taken
from the list.
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Received on Fri Sep 08 2000 - 19:23:24 NZST