linux-kernel - Re: [RFC] [PATCH 0/5] Dynamically allocated pageflags.

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Message-Id: <200707240005.22163.rjw@sisk.pl>
Date:	Tue, 24 Jul 2007 00:05:21 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Nigel Cunningham <nigel@...el.suspend2.net>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 0/5] Dynamically allocated pageflags.

Hi,

On Monday, 23 July 2007 15:05, Nigel Cunningham wrote:
> Hi all.
> 
> As we all know, pageflags have been a scarce resource for a while now. These 
> patches seek to help address that issue by adding support for a new type 
> of 'dynamically allocated' pageflag.
> 
> The basic idea is that we use per node & zone bitmaps built out of order zero 
> allocations, to replace bits in page->flags. Bitmaps can be sparse, being 
> populated when a bit on the page is set, and returning zero for all bits in 
> sparse pages. Untested hotplug support is included.
> 
> This method of storing the data does of course come with a performance hit. 
> I've included some simple timing loops in #ifdef'd code that help quantify 
> that.
> 
> Interestingly, the new implementation is actually quicker under some 
> circumstances. In cases where the usage pattern involves operating on the 
> flags for a number of pages in succession, the hit involved in getting the 
> struct pages from main memory appears to be greater than that involved in 
> calculating which unsigned long and bit to test.
> 
> Tested only on UP (x86_64) so far.

How does it compare to the memory bitmaps used by swsusp, defined in
kernel/power/snapshot.c?

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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