Description of problem:
Can you help, we have a database product that uses memory mapping to access and
update the database file.
On Linux the flushing deamon can not flush the modified memory until a munmap
or msync is called.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. A program that opens a file and map's the first 4k block.
2. Modify that memory block.
3. Crash the box after 30 seconds.
The disk file is not modified.
This disk file is modified.
Can I get bdflush deamon to detect and flush the dirty pages to disk?
Is this a linux bug? The flushing deamon on the Unix operating system, flushes
all write required pages to disk and that includes all those modified memory
mapped pages, but linux doesn't.
From my reading of the SingleUnix spec, we are not required to sync mmaps to
disk unless there is an explicit msync or if the region is unmapped. This is
not a bug. Please reopen if you can find an assertion to the contrary in the
standard, but I think this is simply a portability issue --- any code that
assumes it does not need to msync is just non-portable, as it is relying on