lkml.org 
[lkml]   [2006]   [Feb]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Patch 3/3] prepopulate/cache cleared pages
Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>
>>>couldnt the new pte be flipped in atomically via cmpxchg? That way
>>>we could do the page clearing close to where we are doing it now,
>>>but without holding the mmap_sem.
>>
>>We have nothing to pin the pte page with if we're not holding the
>>mmap_sem.
>
>
> why does it have to be pinned? The page is mostly private to this thread
> until it manages to flip it into the pte. Since there's no pte presence,
> there's no swapout possible [here i'm assuming anonymous malloc()
> memory, which is the main focus of Arjan's patch]. Any parallel
> unmapping of that page will be caught and the installation of the page
> will be prevented by the 'bit-spin-lock' embedded in the pte.
>

No, I was talking about page table pages, rather than the newly
allocated page.

But I didn't realise you wanted the bit lock to go the other way
as well (ie. a real bit spinlock). Seems like that would have to
add overhead somewhere.

>
>>But even in that case, there is nothing in the mmu gather / tlb flush
>>interface that guarantees an architecture cannot free the page table
>>pages immediately (ie without waiting for the flush IPI). This would
>>make sense on architectures that don't walk the page tables in
>>hardware.
>
>
> but the page wont be found by any other CPU, so it wont be freed! It is
> private to this CPU. The page has no pte presence. It will only be
> present and lookupable as a result of the cmpxchg() flipping the page
> into the pte.
>

Yeah, as I said above, the newly allocated page is fine, it is the
page table pages I'm worried about.

--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-02-24 08:04    [W:0.071 / U:1.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site