Problems reclaiming VM cache = XFree86 startup annoyance
Matthew Dillon
dillon at apollo.backplane.com
Wed Dec 24 23:10:10 PST 2003
:I'm not sure what is overloading the disk other than the large amounts
:of paging that are initiated the moment I invoke "startx". The last
:time I did this, I looked at the disk activity beforehand via "systat
:-vm 1". The disks were basically idle (all < 0.05 MB/s). As soon as
:I executed "startx" the swap volume became very active (90--96% busy;
:3--7 MB/sec) and the "SWAP PAGER" out column steadily showed paging
:activity (nothing on the "in" column). (The 4 KB/t was a tell-tale
:sign the system was doing nothing but paging.)
:
:I guess my question is this: why so much paging? If, as someone else
:has mentioned, "Cache" and "Free" pages are both "free" (i.e.,
:allocable memory), with the subtle distinction being that "Cache"
:pages used to hold disk blocks now discarded, then why not allocate
:what is needed from them? As I stated in my original thread, all the
:"Inactive" memory seems to get dumped over to "Cache" when I run
:"startx", and there's usually almost about 400 MB of it when this
:happens.
:...
:Cheers,
:
:Paul.
If it could, it would... my guess is that your box is using a shared
memory video buffer and X is allocating a large swath of
contiguous physical memory to accomodate it, which would force it to
pageout any preexisting dirty data using that memory. That's all I can
think of.
-Matt
Matthew Dillon
<dillon at backplane.com>
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