I want to develop based on iOS and I did some verifications based on xCode Instruments firstly. But there are some confusions on the verification results.
I did the test to open a file in 1KB size. The analysis results from xCode Instruments is as followings:
- In "Disk Usage", it shows that there are 4KB "Page In" operations. (Please refer to P1.png attached)
- In "Virtual Memory Trace", it shows totally 4-times of "File Backed Page In" operations, and each operation size is 16K. (Please refer to P2.png & P3.png attached)
That is, Size of "File Backed Page In" is around 4*16K=64KB.
I did similar tests on different size of files. Every time the values of "Disk Usage"->"Page In" and "Virtual Memory Trace"->"File Backed Page In" are not matched (In this example, the two results are 4KB vs. 64KB).
I think that both values represent disk IO size of the process and they should be in the same value for the same process. Why the values are different? What are the differences between this two options in xCode Instrument tool?
Thanks.
