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Message-ID: <20140722105546.GA9814@amd.pavel.ucw.cz> Date: Tue, 22 Jul 2014 12:55:46 +0200 From: Pavel Machek <pavel@....cz> To: Joerg Roedel <joro@...tes.org> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 0/6 v2] PM / Hibernate: Memory bitmap scalability improvements On Tue 2014-07-22 12:34:44, Joerg Roedel wrote: > On Tue, Jul 22, 2014 at 02:41:29AM +0200, Rafael J. Wysocki wrote: > > It looks like some specific need motivated the Joerg's work, however, > > so let's just not dismiss the use case lightly without knowing it. > > The motivation was to optimize the data structures for machines with > large amounts of RAM without penalizing average machines. On a 12TB > machine you are close to 100000 pages just for one bitmap. Scanning > through that linearly to find a given bit just doesnt scale anymore in > this case. Writing out every single page on 12TB machine to disk does not scale, either :-). > I also see how the problem could be solved differently, but what I > didn't get from the discussion yet is: What is actually *wrong* with > *this* approach? It throws complex / tricky to review code at a problem... that is not a problem in any reasonable configuration. Now... should I spend half an hour reviewing your changes, or are we maybe better without them? > So we save around 50ms (or 62% of time) already on this 16GB machine. Or about 5 seeks or about 0.000% of total hibernation cycle. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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