linux-kernel - Re: Implementing NVMHCI...

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Message-ID: <49E12D03.5070906@garzik.org>
Date:	Sat, 11 Apr 2009 19:51:31 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Grant Grundler <grundler@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux IDE mailing list <linux-ide@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: Implementing NVMHCI...

Alan Cox wrote:
>> We've abstract the DMA mapping/SG list handling enough that the
>> block size should make no more difference than it does for the
>> MTU size of a network.
> 
> You need to start managing groups of pages in the vm and keeping them
> together and writing them out together and paging them together even if
> one of them is dirty and the other isn't. You have to deal with cases
> where a process forks and the two pages are dirtied one in each but still
> have to be written together.
> 
> Alternatively you go for read-modify-write (nasty performance hit
> especially for RAID or a log structured fs).

Or just ignore the extra length, thereby excising the 'read-modify' 
step...  Total storage is halved or worse, but you don't take as much of 
a performance hit.

	Jeff



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