From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andi Kleen <ak@suse.de>, Arjan van de Ven <arjan@intel.linux.com>,
linux-kernel@vger.kernel.org, akpm@osdl.org
Subject: Re: [Patch 3/3] prepopulate/cache cleared pages
Date: Fri, 24 Feb 2006 18:01:38 +1100 [thread overview]
Message-ID: <43FEAF52.80705@yahoo.com.au> (raw)
In-Reply-To: <20060224064912.GB7243@elte.hu>
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
next prev parent reply other threads:[~2006-02-24 7:01 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-23 9:17 [Patch 0/3] threaded mmap tweaks Arjan van de Ven
2006-02-23 9:29 ` [Patch 3/3] prepopulate/cache cleared pages Arjan van de Ven
2006-02-23 9:41 ` Andi Kleen
2006-02-23 12:41 ` Ingo Molnar
2006-02-23 13:06 ` Andi Kleen
2006-02-23 13:15 ` Nick Piggin
2006-02-23 13:29 ` Ingo Molnar
2006-02-24 6:36 ` Nick Piggin
2006-02-24 6:49 ` Ingo Molnar
2006-02-24 7:01 ` Nick Piggin [this message]
2006-02-24 12:33 ` Andi Kleen
2006-02-24 12:55 ` Hugh Dickins
2006-02-24 9:15 ` Arjan van de Ven
2006-02-24 9:26 ` Nick Piggin
2006-02-24 12:27 ` Andi Kleen
2006-02-24 15:31 ` Andrea Arcangeli
2006-02-25 16:48 ` Nick Piggin
2006-02-25 17:22 ` Nick Piggin
2006-02-28 22:30 ` Pavel Machek
2006-02-23 18:25 ` Paul Jackson
2006-02-23 9:30 ` [Patch 2/3] fast VMA recycling Arjan van de Ven
2006-02-23 9:42 ` Andi Kleen
2006-02-23 9:48 ` Arjan van de Ven
2006-02-23 10:05 ` Andi Kleen
2006-02-23 10:15 ` Arjan van de Ven
2006-02-23 11:00 ` Andi Kleen
2006-02-23 11:22 ` Arjan van de Ven
2006-02-23 11:57 ` Andi Kleen
2006-02-24 18:52 ` Christoph Hellwig
2006-02-24 19:05 ` Andi Kleen
2006-02-24 19:09 ` Christoph Hellwig
2006-02-23 16:37 ` Benjamin LaHaise
2006-02-23 20:02 [Patch 3/3] prepopulate/cache cleared pages Chuck Ebbert
2006-02-23 21:10 Chuck Ebbert
2006-02-23 21:18 ` Arjan van de Ven
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=43FEAF52.80705@yahoo.com.au \
--to=nickpiggin@yahoo.com.au \
--cc=ak@suse.de \
--cc=akpm@osdl.org \
--cc=arjan@intel.linux.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).