Re: [PATCH 4/10] alternate 4-level page tables patches

[Nick Piggin <nickpiggin@yahoo.com.au>]

Nick Piggin wrote:
> 4/10
> 
> 
> ------------------------------------------------------------------------
> 
> 
> 
> Rename clear_page_tables to clear_page_range. clear_page_range takes byte
> ranges, and aggressively frees page table pages. Maybe useful to control
> page table memory consumption on 4-level architectures (and even 3 level
> ones).
> 

I maybe didn't do this patch justice by hiding it away in this series.
It may be worthy of its own thread - surely there must be some significant
downsides if nobody had implemented it in the past (or maybe just a fact
of "that doesn't happen much").

Anyway, if we show off its best-case: start 100 processes that each allocate
1GB of memory, touch all pages, then free it (but don't exit). Do that on
i386 with PAE (but most any 3+ level setup will be more or less vulnerable
to the same problem).

npiggin@intel:~/tests/pte$ grep PageTables meminfo.100*
meminfo.100:PageTables:     181228 kB
meminfo.100.optimized:PageTables:       2476 kB

You see, the 1GB we've allocated isn't perfectly PGDIR aligned, so none of
the page tables can get freed. So it is a potentially significant saving
in some cases.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>