Contents

Page fault notifier

Contents

This week I tried to lock in the physical memory the Xorg’s input code using mlock(). To do this I traced the code minutely and locked all the text and data related to input. I didn’t get success. The mouse still lags when the system is paging (you might remember that with mlockall() all worked wonderful except that it eats much memory). So what might be happening is that something is not locked yet. To guarantee it I searched for a user-space tool that traces page fault. I only found the ‘truss’ command on Solaris. Linux (my OS) doesn’t provide no one (‘strace’ don’t do this).

So I surrendered to the kernel space tools putting some ‘print’ in the kernel code (before I tried a little systemtap and kprobe without success). Then I made a kernel module [0] using the notifier scheme which already exists inside the kernel. The problem is that the page fault notifier doesn’t show the address which happened the fault. So I made a patch to increment this functionality [1].

Using ‘objdump -t -d Xorg’ shows all the symbols and addresses I want. Now I must compare the module’s output with the dump and be happy :)

[0] http://web.inf.ufpr.br/vignatti/code/page_fault_notifier.c

[1] http://lkml.org/lkml/2007/7/27/8, consider that the first time that I hacked the kernel code was this week. So if something sounds weird…