Date: Wed, 03 Mar 2004 12:44:07 -0600
From: Dave McCracken <dmccr@us.ibm.com>
To: Andrea Arcangeli <andrea@suse.de>
cc: "Martin J. Bligh" <mbligh@aracnet.com>, linux-kernel@vger.kernel.org
Subject: Re: 230-objrmap fixes for 2.6.3-mjb2
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--On Wednesday, March 03, 2004 19:39:01 +0100 Andrea Arcangeli
<andrea@suse.de> wrote:

>> What we've actually discussed before was more along the lines of
>> PG_locked to match VM_LOCKED, but the main idea was to be able to skip
>> over ineligible pages without having ot look up their mappings during
>> pageout.
> 
> I'm not very excited using PG_locked for that, that doesn't only mean
> "unswappable", it means also that the page is under I/O (or uner some
> other operation that needs serialization like unmapping the page) which
> is quite a different concept from VM_LOCKED. a wait_on_page would
> deadlock on such a PG_locked page, while wait_on_page on a page of a
> mlocked vma doesn't normally deadlock.
> 
> But I see what you want to do here, and PG_reserved would be too much
> for that since it changes the semantics for cow and free_pages, but
> PG_locked doesn't look good enough either, the VM_LOCKED and PG_locked
> concept is quite different, PG_reserved and VM_RESERVED is quite close
> instead (except for the page->count accounting).

Sorry, I misspoke.  I didn't mean the current PG_locked.  I meant a new
flag, or more probably a counter, that represents all the VM_LOCKED regions
a page is in.

Dave McCracken

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