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This has been a tough one to debug.
My linux kernel acting as a router with grsecurity and Highmem enabled hangs after 3 hours of heavy traffic.
I have tried Magic-sysrq and KDB debugging unsuccessfully to find the cause of the hang.
The reason i suspect the connection is pretty straight
forward as a configuration.
Highmem has been there in my 1GB ram kernel for ages now.
When PAX is enabled via the grsecurity patch , We actually split the 3GB user space to 1.5-1.5 of exec n no exec memory via the segmentation feature .Right?
But the statistics drags highmem into this .On a hightraffic load ,The amount of Highmen available is very less just before the kernel hangs (It reduces from
15MB available to 2 MB as shown below)
If i disable grsec , the Highmem no longer reduces exponentially at heavy network activity.
1]Is there a connection between Highmem and Segmentation Exec feature of PAX ?
2] Highmem can be disabled but i want to retain Segmentation Exec feature for security concerns.
But Highmem is supposed to be dependent on NVRAM in our device that is mapped to a physical memory range b/w 3GB -4GB ...My software team insists this can't be changed due because they dont want to have a BIOS upgrade which has this range mapped in it.Is there an alternative to this ? or I am speaking absolute crap ?