Messages in this thread | | | Date | Sat, 14 Aug 2004 08:09:21 -0700 | From | "Martin J. Bligh" <> | Subject | Re: Serious Kernel slowdown with HIMEM (4Gig) in 2.6.7 |
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> 2. I have discovered an issue with the Linux 2.6.7 kernel when HIMEM is > enabled which exhibits itself as a slowdown in directory access regardless > of filesystem used. When HIMEM is disabled the performance returns to > normal. The test I ran was a simple "/usr/bin/time ls -l" of a directory > with 3000 empty files. With HIMEM enabled in the kernel this takes > approximately 1.5 seconds. Without HIMEM it takes 0.03 seconds. The > time is 100% CPU and no I/O operations are done to disk. "time" reports > there are 460 "minor" page faults with zero "major" page faults. > I believe the issue here is the mapping of pages between high-mem and > lowmem in the kernel paging code. This increase in time for directory > accesses doubles to triples times for applications using samba. > I have also tested this on another system which had only 512Meg of RAM > but with HIMEM set in the kernel and did not experience the problem. > I believe it only effects the performance when the paging buffers end > up in highmem.
Does time indicate more systime or user time? If it's systime (probably is) please take a kernel profile of each (see Documentation/basic_profiling.txt). That'll give us a much better clue what's going on.
M.
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