Messages in this thread | | | Date | Wed, 6 Feb 2019 15:17:06 -0800 | From | Larry Bassel <> | Subject | question about mmap MAP_PRIVATE on PMEM/DAX/fs files |
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Is mmaping a PMEM/DAX/fs file MAP_PRIVATE supported? Is it something that people are likely to want to do?
If it is supported, suppose I open a file in PMEM/DAX/fs, mmap it MAP_PRIVATE, read from the memory mapped file (with memory accesses, not the read syscall) and take a page fault which the kernel satisfies.
At this time do my page tables for the private mmaped page(s) point to the PMEM corresponding to the file and the kernel will wait until the page(s) is/are altered (either by me or someone else) to copy on write and give me a different page/mapping?
Or does the kernel avoid this by always mapping a copy of the page(s) involved in the private mmap in the first place?
In either case, is my private copy going to come from PMEM or is it an "ordinary" page, or is this "random"? Does the program have any choice in this (i.e. suppose I want to make sure my copied page is persistent)?
Thanks.
Larry
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