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

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

William Lee Irwin III wrote:
> On Sat, Dec 18, 2004 at 05:57:12PM +1100, Nick Piggin wrote:
> 
>>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).
>>Possible downsides are:
>>- flush_tlb_pgtables gets called more often (only a problem for sparc64
>>  AFAIKS).
>>- the opportunistic "expand to fill PGDIR_SIZE hole" logic that ensures
>>  something actually gets done under the old system is still in place.
>>  This could sometimes make unmapping small regions more inefficient. There
>>  are some other solutions to look at if this is the case though.
>>Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
> 
> 
> I wrote something equivalent to this in September, but dropped it on the
> floor after some private replies etc. indicated no one gave a damn about
> the testcase I posted in Message-ID: <20040908110718.GX3106@holomorphy.com>
> where the pagetable leak fooled the OOM killer into shooting the wrong
> processes long enough to trigger a panic() in oom_kill.c
> 
> 

Hmm... I actually didn't see your post, but it seems like something
worth pursuing.

My incling is that the hybrid expand-to-hole / refcounting approach
I outlined earlier in the thread might be the way to go.

I'll be interested to hear what the powers that be think.
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