Re: Linux-2.5.17

[Russell King <rmk@arm.linux.org.uk>]

On Mon, May 20, 2002 at 10:16:35PM -0700, Linus Torvalds wrote:
> Various FS updates (including merges of quota and iget_locked), and
> Makefile cleanups from Kai.
> 
> And yet more TLB shootdown stuff.

We seem to have inconsistent cache handling in the new TLB shootdown stuff.
Or maybe its just my misunderstanding of what's going on; whatever it is,
the new TLB shootdown stuff appears to be quite messy.

Lets look at the flow of the 3 places where tlb_gather_mmu is used:

zap_page_range		unmap_region		exit_mmap
  flush_cache_range	  tlb_gather_mmu	  tlb_gather_mmu
  tlb_gather_mmu	  unmap_page_range	  flush_cache_mm
  unmap_page_range	  free_pgtables		  unmap_page_range
  tlb_finish_mmu	  tlb_finish_mmu	  clear_page_tables
						  tlb_finish_mmu

So we have 3 different functions, 2 different orders of gather_mmu
and cache handling, and one with no cache handling what so ever.

I think we have two options - either leave the cache handling up to
tlb_start_vma() (in which case, flush_cache_range and flush_cache_mm
are redundant and should be removed) or let it be up to the caller
of tlb_gather_mmu to call the right cache handling function.

I think which is actually function dependent - in zap_page_range,
we're only removing one vma.  In exit_mmap, we're removing all vmas.
In unmap_region, we're removing an unspecified number of vmas.
Depending on which option we choose, we'll either end up calling
flush_cache_range() many times, or flush_cache_mm() and flushing
the cache for a munmap of a small area.

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html