Messages in this thread |  | | Date | Thu, 2 Nov 2000 08:19:06 +0100 (CET) | From | Mike Galbraith <> | Subject | Re: [BUG] /proc/<pid>/stat access stalls badly for swapping process, 2.4.0-test10 |
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On Wed, 1 Nov 2000, Rik van Riel wrote:
> On Wed, 1 Nov 2000, David Mansfield wrote: > > > I'd like to report what seems like a performance problem in the latest > > kernels. Actually, all recent kernels have exhibited this problem, but > > I was waiting for the new VM stuff to stabilize before reporting it. > > > > My test is: run 7 processes that each allocate and randomly > > access 32mb of ram (on a 256mb machine). Even though 7*32MB = > > 224MB, this still sends the machine lightly into swap. The > > machine continues to function fairly smoothly for the most part. > > I can do filesystem operations, run new programs, move desktops > > in X etc. > > > > Except: programs which access /proc/<pid>/stat stall for an > > inderminate amount of time. For example, 'ps' and 'vmstat' > > stall BADLY in these scenarios. I have had the stalls last over > > a minute in higher VM pressure situations. > > I have one possible reason for this .... > > 1) the procfs process does (in fs/proc/array.c::proc_pid_stat) > down(&mm->mmap_sem); > > 2) but, in order to do that, it has to wait until the process > it is trying to stat has /finished/ its page fault, and is > not into its next one ... > > 3) combine this with the elevator starvation stuff (ask Jens > Axboe for blk-7 to alleviate this issue) and you have a > scenario where processes using /proc/<pid>/stat have the > possibility to block on multiple processes that are in the > process of handling a page fault (but are being starved)
I'm experimenting with blk.[67] in test10 right now. The stalls are not helped at all. It doesn't seem to become request bound (haven't instrumented that yet to be sure) but the stalls persist.
-Mike
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