Re: sys_exit() and zap_page_range()

[Philipp Rumpf <prumpf@uzix.org>]

On Sun, Jul 09, 2000 at 11:54:54PM +0000, Andrew Morton wrote:
> Philipp Rumpf wrote:
> Hi, Philipp.
> 
> > Here's a simple way:
> 
> Already done it :)  It's apparent that not _all_ callers of z_p_r need
> this treatment, so I've added an extra 'do_reschedule' flag.  I've also
> moved the TLB flushing into this function.

It is ?  I must be missing something, but it looks to me like all calls
to z_p_r can be done out of syscalls, with pretty much any size the user
wants.

> It strikes me that the TLB flush race can be avoided by simply deferring
> the actual free_page until _after_ the flush.  So
> free_page_and_swap_cache simply appends them to a passed-in list rather
> than returning them to the buddy allocator.  zap_page_range can then
> free the pages after the flush.

In fact, both the tlb flushing and the cache invalidating/flushing (we don't
really need to flush the cache if we're zapping the last mapping) belong in
zap_page_range.  Right now three callers don't do the tlb/cache flushes:
 exit_mmap and move_page_tables should be fine with doing the cache/tlb
invalidates;  read_zero_pagealigned doesn't want to have intermediate invalid
ptes, so I would say it's buggy now.

> > [PAGE_SIZE*4 is low, I suspect.]
> 
> zap_page_range zaps 1000 pages per millisecond, so I'm doing 1000 at a
> time.

I think we should be able to live with that for 2.4, unless the tlb flushing
race is really bad.  It looks like a rather theoretical possibility limited
to SMP systems to me.

	Philipp
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