linux-kernel - Re: Change PAGE_SIZE from minimum 4k to 12k

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Message-ID: <20170525215503.GA25045@amd>
Date:   Thu, 25 May 2017 23:55:03 +0200
From:   Pavel Machek <pavel@....cz>
To:     Kevin McKinney <klmckinney1@...il.com>
Cc:     Alan Cox <gnomes@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: Change PAGE_SIZE from minimum 4k to 12k

Hi!

> >> > Would it be possible to have a custom block device driver read/write
> >> > in increments of 12k instead of reading/writing data in 4k increments?
> >> > In other words, I would like to change the default page size on a
> >> > x86_64 platform (4.4.0 kernel) from 4k to 12k as the minimum page
> >> > size?  I understand I may have negative performance due to
> >> > fragmentation. Any help would be appreciated.
> >> >
> >> > If this is the wrong mailing list, please let me know the right one to use.
> >>
> >> I won't say "no" but ammount of work neccessary is likely measured in
> >> man-years. Plus, hardware page size _is_ 4KB.
> >
> > Or a few other much larger sizes. Not that it actually matters. You can
> > implement a larger software page size for a platform but it would still
> > neeed to be a power of two, and you'd have trouble running some existing
> > binaries for x86.
> >
> > What problem are you *actually* trying to solve ?
> 
> Thanks for responding!  I work for a company that created custom
> hardware with 4 banks of drives. Each bank is 12 terabytes; and each
> bank is controlled by a separate RAID controller.  We created a custom
> block device driver that is responsible for moving data to each bank.
> The RAID controller will then stripe the data across the appropriate
> disks for the specified bank.  The problem we are having is by moving
> in increments of 4k, we are unable to utilize all 48 terabytes; we are
> only able to utilize 32 terabytes. If we could move in increments of
> 12K that would allow us to use the full 12 terabytes for each bank.

12TB is not that big.. are we talking spinning rust or something
special?

I mean, what does it have to do with page size? 48TB device, that's 5
SATA drives... that's not even that big.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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