why do we need vmalloc_sync_all?

[Oleg Nesterov]

I didn't read v2 yet, but I'd like to ask a question.

Why do we need vmalloc_sync_all()?

It has a single caller, register_die_notifier() which calls it without
any explanation. IMO, this needs a comment at least.

I am not sure I understand the changelog in 101f12af correctly, but
at first glance vmalloc_sync_all() is no longer needed at least on x86,
do_page_fault() no longer does notify_die(DIE_PAGE_FAULT). And btw
DIE_PAGE_FAULT has no users. DIE_MNI too...

Perhaps we can simply kill it on x86?

As for other architectures I am not sure. arch/tile implements
vmalloc_sync_all() and uses notify_die() in do_page_fault().

And in any case register_die_notifier()->vmalloc_sync() looks strange.
If (say) arch/tile needs this to fix the problem with modules, perhaps
it should do vmalloc_sync_all() in do_init_module() paths?

Oleg.

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