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I know, process can use disk cache as free memory as required. In my 32 bit machine I can see, disk cache can use all free memory. But in 64 bit machine can't. In 64 bit machine, I have 252GB RAM(free command), 24 cores, and 90 jbod disks. Running 45 java servers with -Xmx2000m to read/write small files form/to disks.

Every 4/8/10/13 hrs, I'm getting sudden disk cache drop also. I can see after disk cache drop, next 5-6 hrs disk cache reach to ~110 GB, but after that for next 4-5 hrs it is not crossing this ~110GB limit(but still have ~80GB free), then sudden whole disk cache getting drop.

I have no idea what is going on here. Please suggest me : is there any system configuration to solve this, or have jbod/memory problem, if so then how to solve.

Using linux OS and 64 bit JVM.

free -g
             total       used       free     shared    buffers     cached
Mem:           252        162         89          0         42         80
-/+ buffers/cache:         39        212
Swap:            1          0          1
Upendra
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  • Do you have an actual performance problem or is this purely a cosmetic issue? – David Schwartz Oct 20 '14 at 10:44
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    Most likely explanation is, some process comes along and need lots of memory. So the kernel gives it some of the memory previously used for caching some pages which had only been accessed once. After the process terminates the memory will be free and only be used again for disk cache when a process access some data not already in the cache. – kasperd Oct 20 '14 at 10:56
  • @DavidSchwartz : there is no any performance problem. – Upendra Oct 21 '14 at 13:39
  • @kasperd : I'm not able to find those process. there is some monitoring schedules are running. will try to find, and let you know. – Upendra Oct 21 '14 at 13:45
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    It is also possible those pages were freed from the cache because the underlying files got deleted. – kasperd Oct 21 '14 at 15:36
  • Thanks kasperd... But we are not deleting that much files. Maximum 1 GB(if we combined all instances) of files delete can happen in one day, and that one also in particular time range(3AM to 7AM). And also hrs from this range picked by each instances randomly. – Upendra Oct 23 '14 at 04:58

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