Messages in this thread | | | Date | Wed, 28 Apr 2004 18:29:02 -0700 | From | "Brett E." <> | Subject | Re: ~500 megs cached yet 2.6.5 goes into swap hell |
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Andrew Morton wrote:
> "Brett E." <brettspamacct@fastclick.com> wrote: > >>>I see no swapout from the info which you sent. >> >> pgpgout/s gives the total number of blocks paged out to disk per second, >> it peaks at 13,000 and hovers around 3,000 per the attachment. > > > Nope. pgpgout is simply writes to disk, of all types. That is what is confusing me.. From the sar man page:
pgpgin/s Total number of kilobytes the system paged in from disk per second.
pgpgout/s Total number of kilobytes the system paged out to disk per second.
> > swapout is accounted for under pswpout and your vmstat trace shows a little > bit of (healthy) swapout with swappiness=100 and negligible swapout with > swappiness=0. In both cases, negligible swapin. That's all just fine. > > >> Swapping out is good, but when that's coupled with swapping in as is the >> case on my side, it creates a thrashing situation where we swap out to >> disk pages which are being used, we then immediately swap those pages >> back in, etc etc.. > > > Look at your "si" column in vmstat. It's practically all zeroes. > > >> The usage pattern by the way is on a server which continuously hits a >> database and reads files so I don't know what "swappiness" should be set >> to exactly. Every hour or so it wants to untar tarballs and by then the >> cache is large. From here, the system swaps in and out more while cache >> decreases. Basically, it should do what I believe Solaris does... simply >> reclaim cache and not swap. Capping cache would be good too but the >> best solution IMO is to simply reclaim the cache on an as-needed basis >> before thinking about swapping. > > > swappiness=100: swaps a lot. swappiness=0: doesn't swap much. > > With a funny workload like that you might choose to set swappiness to 0 > just around the hourly tar operation, but as the machine seems to not be > swapping there doesn't seem to be a need.
Yeah, it wouldn't help if paging isn't the problem. I'd like more clarificaton on sar before I throw out paging being the culprit.
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