RE: Possible deadloop in direct reclaim?

[Lisa Du <cldu@marvell.com>]

>-----Original Message-----
>From: Russell King - ARM Linux [mailto:linux@arm.linux.org.uk]
>Sent: 2013年8月1日 16:57
>To: Lisa Du
>Cc: KOSAKI Motohiro; Christoph Lameter; linux-mm@kvack.org; Mel
>Gorman; Bob Liu; Neil Zhang
>Subject: Re: Possible deadloop in direct reclaim?
>
>On Wed, Jul 31, 2013 at 10:19:53PM -0700, Lisa Du wrote:
>> >fork alloc order-1 memory for stack. Where and why alloc order-2? If it is
>> >arch specific code, please
>> >contact arch maintainer.
>> Yes arch do_fork allocate order-2 memory when copy_process.
>> Hi, Russel
>> What's your opinion about this question?
>> If we really need order-2 memory for fork, then we'd better set
>> CONFIG_COMPATION right?
>
>Well, I gave up trying to read the original messages because the quoting
>style is a total mess, so I don't have a full understanding of what the
>issue is.
I'm really sorry for my quoting style, I'll avoid such issue in future!
>
>However, we have always required order-2 memory for fork, going back to
>the 1.x kernel days - it's fundamental to ARM to have that.  The order-2
>allocation os for the 1st level page table.  No order-2 allocation, no
>page tables for the new thread.
>
>Looking at this commit:
>
>commit 05106e6a54aed321191b4bb5c9ee09538cbad3b1
>Author: Rik van Riel <riel@redhat.com>
>Date:   Mon Oct 8 16:33:03 2012 -0700
>
>    mm: enable CONFIG_COMPACTION by default
>
>    Now that lumpy reclaim has been removed, compaction is the only
>way left
>    to free up contiguous memory areas.  It is time to just enable
>    CONFIG_COMPACTION by default.
>
>it seems to indicate that everyone should have this enabled - however,
>the way the change has been done, anyone building from defconfigs before
>that change will not have that option enabled.
>
>So yes, this option should be turned on.
Thanks Russel! 
I think I have got the information I want. Really appreciate for your explanation!