linux-kernel - Re: [git patches] xfs and block fixes for virtually indexed arches

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Date:	Thu, 17 Dec 2009 19:45:55 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	tytso@....edu, Linus Torvalds <torvalds@...ux-foundation.org>,
	Kyle McMartin <kyle@...artin.ca>, linux-parisc@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [git patches] xfs and block fixes for virtually indexed arches

Christoph Hellwig <hch@...radead.org> writes:

> On Thu, Dec 17, 2009 at 11:30:36AM -0500, tytso@....edu wrote:
>> That's because apparently the iSCSI and DMA blocks assume that they
>> have Real Pages (tm) passed to block I/O requests, and apparently XFS
>> ran into problems when sending vmalloc'ed pages.  I don't know if this
>> is a problem if we pass the bio layer addresses coming from the SLAB
>> allocator, but oral tradition seems to indicate this is problematic,
>> although no one has given me the full chapter and verse explanation
>> about why this is so.
>
> Actually at least iscsi now has a workaround for that by checking for
> PageSlab.  Back when we deal with the XFS issue that check was only
> available with debug options enabled.  I tried to sort it out by
> agreeing with the block and iscsi folks that either

DRBD has the same workaround as well:

        if (disable_sendpage || (page_count(page) < 1) || PageSlab(page))

But it seems like a gross hack to me. Perhaps this should be 
passed as some sort of BIO attribute?

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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